Aircraft tire

Care & Service Manual

Note : This document, MichelinReference

#MAT-CSM-01 Rev. A

supercedes Reference #MAT-CSM-95 Rev. B,#MAT-CSM-95 Rev. A,Michelin document MAINT-0013 and the document entitled Michelin Aircraft TireCare & Maintenance.

3Tableof contents

Introduction 6

Aircraft TireConstruction 7The Tread 8The Undertread 8A Carcass Ply 8

- For Bias- For Radial

The Beads 9Chafer Strips 9The Liner 9The Sidewall 9Products Unique to the Bias Tire 10

- The Tread Reinforcing Ply- Breaker Plies- ORIONTM technology- Fabric Tread- Spiral Wrap

Products Unique to the Radial Tire 11

- The Protector Ply- Belt Plies

Chine Tires 11

is Not Recommended 22Store Tubes Properly 23Tire and Tube Age Limit 23Storage of Inflated Tire and Wheel Assemblies 23

Ozone 24Recommendations for Storage and Handling 25

General MountingInstructions For Aircraft Tires 26General 27Premounting Checklist 27

- Wheels- Tires

Mounting 29- Use of Inner Tubes

Bias TiresRadial Tires

- Lubrication of Tire BeadsBias TiresRadial Tires

- Tire/Wheel Assembly- Tire/Wheel Alignment

Branding 12

Tire serial number codes 17

General SafetyConsiderations 18Mounting 19Inflating 19Tires In Service 19

- Transportation

Storing Aircraft Tires And Tubes 20Handling Aircraft Tires 21Avoid Moisture and ozone 21

- Ozone - What is it ?- Impact of ozone on tires

Designing for ozone 21Store away from fuel and solvents 22Store in the Dark 22Store Tires Vertically 22Horizontal Stacking of Tires

- Inflating With Nitrogen- Special Procedure Properly Seat

Tube-Type Tires

Basic Pressure Retention Check 31

- Procedure

Emergency Pressure Retention Check 32

- Procedure

Alternate Pressure Retention Check 32

- Procedure

Sidewall Venting 33Not all aircraft tires are vented 33Storage of an Inflated Tire and Wheel Assembly 34

Mounting Tire/WheelAssembly On The Aircraft 36Visually Inspect Tire/Wheel Assembly 37Readjust Tire Pressure 37

Inflation PressureMaintenance 38Proper Inflation - Getting

the Most Out of Your Tires 39- Effects of Underinflation- Effects of Overinflation

Checking Duals for EqualOperating Pressure 40Proper Inflation - Setting the Pressure Level 41

- Inflating and Reinflatingthe Tire/Wheel Assembly

- Loaded versus Unloaded Tires- Properly Inflating Tube - Type Tires

Effect of ambient temperature on gauge pressure 42

- Effect of temperature- Proper Inflation - Standard

for Maintaining Pressure Level- Aircraft experiencing large ambient

temperature differences betweenairports

Schedule and action 44- When to Check

FrequencyChecking Hot TiresCompare tire pressures on thesame given landing gearSingle and Multiple tire gearTwo Tire GearThree or more tire gear

- Monitoring Inflation Pressure -What To Do

Pressure Loss 46

- Normal Response- Testing For Pressure Loss- Causes of Pressure Loss

Tire GrowthDrop in Ambient TemperatureApproved Calibrated GaugeForeign Object DamageImproperly Seated BeadsValve Stem or Valve CoreValve SealWheel Half Parting Line O-Ring SealFuse PlugPressure Release PlugSeepage Between Tire Bead and

Wheel FlangeLeakage Through the Well AreaDamaged Wheel Sealing SurfacesDamage to the Tire InnerlinerCracks or Splits in the Inner Tube

- Troubleshooting -Have You Considered?

Tire ServiceabilityCriteria 51On Aircraft Inspection With Tire Mounted 52

Removal Criteria - Wear

Water can affect traction 52- Typical Wear Conditions

Normal WearOverinflationUnderinflation

4

Tableof contents

5

Worn Beyond Recommended LimitsFlat SpottingAsymmetrical WearServiceability Criteria/ Limits For Tire Damages

Tread WearTread Cuts/ Foreign ObjectsSidewall Cuts / Foreign Objects

Serviceability Criteria/Operational Conditions 63

- Hard Landing- Rejected Takeoff

Off-Aircraft Inspection With Tire Dismounted 64

- A Systematic Approach to TireInspection

Bias tiresRadial tires

Matching and Mixability of Dual Tires 66Matching Tires 67

- Matching CriteriaBias TiresRadial TiresNew versus Retreaded Tires

- MixabilityBias - BiasRadial - RadialBias - Radial

- Observe Load and Inflation Recommendations

Vibration and Balance 70

- Proper inflation pressureInflation is equalizedFull growthBeads properly seatedFlat spotting/uneven wearProperly mountedAir trapped between tire and tubeTube wrinkledWheel out of balanceCondition of wheelLoose wheel bearingGear alignmentWorn gear components

General DismountingInstructions For Aircraft Tires 72Removal From Landing Gear 73Reason for removal-Tracking 73Tire Dismounting 73

- Tire/ Wheel DismountingSequence

Tire Dismounting Equipment 75

Retreading and Repairing Aircraft Tires 77Retreading Aircraft Tires 78Accepting Tires For Retreading 78Repairing Aircraft Tires 78Non-Repairable Aircraft Tires 79Repairable Aircraft Tires 79

Operating andHandling Tips forBetter Tire Service 80Taxiing 81Pivoting By Using Brakes 81Condition of Airport Field 82Avoid Chemical Contamination 82Nylon Flat Spotting 82Chevron Cutting 83Hydroplaning 83Landings Per Tread 84

For aircraft tires to delivermaximum performance, reliability,durability and safety, they must beproperly cared for and serviced.

This manual is designed as a guideto the procedures to be used for allaspects of aircraft tire care andoperation. It provides detailedinformation about how to operateaircraft tires to achieve optimumservice. It also covers installation,removal and servicing techniques. It should be used in conjunctionwith the operating procedures givenby the aircraft and wheelmanufacturers.

The procedures given in thismanual apply to all Michelinmanufactured aircraft tires, new orretreaded, regardless of the familyname, current (Michelin Air,Michelin Air X, Michelin Aviator,Aviator, BF Goodrich, AAT,Silvertown) or future. The sameservice and care techniques shouldbe used for both Bias and Radialtires. In some specific cases, due tothe nature of bias and radial tireconstructions, differences in servicetechniques may exist. Whereapplicable, these differences havebeen noted.

Whether you operate a singleaircraft, or a fleet, the principles andprocedures contained in this manualwill be of benefit.

If further information is needed,please contact your MichelinRepresentative.

See back cover for regional contacts.

6

Introduction

TireTire constructionconstruction

7Aircraft tireconstruction

Aircraft tireconstruction

TTiirree ccoonnssttrruuccttiioonn

An aircraft tire must withstand a widerange of operational conditions.Whenon the ground, it must support theweight of the aircraft. During taxi, itmust provide a stable, cushioned ridewhile resisting heat generation,abrasion and wear. At take-off, the tirestructure must be able to endure notonly the aircraft load but also the forcesgenerated at high angular velocities.Landing requires the tire to absorbimpact shocks while also transmittinghigh dynamic braking loads to theground. All of this must beaccomplished while providing a long,dependable, reliable, service life.

These extreme demands require a tirewhich is highly engineered andprecisely manufactured.For this reason, tires are designed as a composite of various rubber,fabric and steel products. Each of the components serves a very specificfunction in the performance of the tire.

To meet the aircraft demands of todayand tomorrow, Michelin designs andproduces two different and distincttire constructions, the conventional

The undertread is a layer of specially formulated rubber designed to enhance the bondingbetween the treadreinforcement/protector plies andthe carcass body. For those tiresdesigned to be retreaded, this rubberlayer will be of sufficient thickness toact as the interface for buffing the old tread assembly, as well as theliaison with the new retread products.

A carcass ply consists of fabriccords sandwiched between twolayers of rubber. Today, the mostcommon fabric cord is nylon. The carcass body itself is made frommultiple layers of carcass plies, eachone adding to the strength and loadbearing capability of the tire. The carcass plies are anchored bywrapping them around bead wires,thus forming the PLY TURN-UPS.

FOR BIAS constructed tires, the carcass plies are laid at anglesbetween 30° and 60° to the centerlineor direction of rotation of the tire.Succeeding plies are laid with cord

8

cross-ply or BIAS tire and the RADIALtire. Both nomenclatures describe theangular direction of the carcass plies.

While many of the components of biasand radial tires have the sameterminology, the carcass ply angles arenot the only difference between a biasconstructed tire and a radialconstructed tire. The technologiesutilized are quite different involvingdifferent design parameters,compounds, and materials.

The tread refers to the crown areaof the tire in contact with the ground.Most Michelin tires are designedwith circumferential grooves moldedinto the tread area. These provide amechanism to channel water frombetween the tire and runway surfacewhich helps to improve groundadhesion.

The tread compound is formulatedto resist wear, abrasion, cutting,cracking and heat buildup. It prolongs the life of the casing by protecting the underlying carcassplies.

Aircraft tireconstruction

angles opposite to each other, toprovide balanced carcass strength.

FOR RADIAL constructed tires,each carcass ply is laid at an angleapproximately 90° to the centerlineor direction of rotation of the tire.Each successive layer is laid at asimilar angle. Radial constructedtires of the same size have a fewernumber of plies than do tires of abias construction, because the radialcord direction is aligned with theburst pressure radial force allowingfor optimized construction.

The beads or bead wires anchorthe tire to the wheel. They are fabricated from steel wires layeredtogether and can be embedded withrubber to form a bundle. The bundleis then wrapped with rubber coatedfabric for reinforcement.

9

The liner in tubeless tires is a layerof rubber specially compounded toresist the permeation of nitrogen andmoisture through to the carcass. It isvulcanized to the inside of the tireand extends from bead to bead. Itreplaces the inner tube common totube-type tires.All Michelin manufactured Radialaircraft tires are certified for in-service operation to -55°C.Beginning with manufactured date,June 1999, all Michelin Bias aircrafttires are certified for in-serviceoperation to -55°C.In tube-type tires, a different, thinnerliner material is used to protect thecarcass plies from moisture and tubechafing, but is generally insufficientto maintain air retention.

The sidewall is a layer of rubbercovering the outside of the carcassplies. Its purpose is to protect thecord plies. In addition, the sidewallrubber contains anti-oxidants. They are slowly released over time toprotect the tire from ultraviolet andozone attack, which cause rubbercracking.

Depending on the size and designapplication, BIAS tires areconstructed with 2 to 6 bead bundles(1 to 3 per side). By contrast, RADIALconstructed tires have 2 beadbundles (1 on each side) regardlessof tire size.

Chafer strips are strips of protec-tive fabric or rubber laid over theouter carcass plies in the bead areaof the tire. Their purpose is to pro-tect the carcass plies from damagewhen mounting or demounting andto reduce the effects of wear andchafing between the wheel and thetire bead.

Products unique to the bias tire

The tread reinforcing plyconsists of single or multiple layersof a special nylon fabric and rubberlaid midway beneath the treadgrooves and top carcass ply. Theseplies help to strengthen and stabilizethe crown area, by reducing treaddistortion under load, and toincrease high speed stability. Theyalso offer a resistance to treadpuncture and cutting and help toprotect the carcass body.

Breaker plies (not shown) aresometimes used to reinforce thecarcass in the tread area of the tire.

ORION™ technology is adevelopment unique to MichelinBias construction. It consists of aCROWN REINFORCEMENT placedon the inside of the tire. ThisCROWN REINFORCEMENTstrengthens and provides a moreuniform pressure distribution in thefootprint SLOWING THE RATE OFWEAR, improving landingsperformance in a lighter tire design.

Fabric tread (not shown) is aunique development for applicationon high speed military aircraft.Multiple plies of nylon cord arelayered throughout the tread stock,reducing rubber distortion underload and high speeds, thus reducingheat normally generated by flexing.The laminates also control theformation of high speed “standingwaves.” Improved resistance to cutsand punctures is also a benefit ofthis type of construction.

Spiral Wrap (not shown) is atechnique used with retreaded tires.Individual textile cords are layedwithin the replacement tread rubberas it is applied to the tire casing.Cords are oriented to the top 1/2 -1/3 of the skid and are free to “float.”Because of their circumferentialorientation, the textile cords provideadded resistance to the cutting andtearing action associated withchevron cutting.

tread

tread reinforcing ply

undertread

carcass plies

sidewall

beads chafer strips

liner

carcass ply turn-ups

Bias Tire Construction

10

Aircraft tireconstruction

ORION™ technology

Products unique to the radial tire

The protector ply is typicallyfound in retreadable tires and placed in the crown area justbelow the tread rubber. It providescut resistance protection to theunderlying belts and carcass plies.

Belt plies are laid between thetread area and top carcass ply. They restrain the outer diameter ofthe tire, providing a tread surfacewith greater resistance to squirmand wear as well as providing a moreuniform pressure distribution in thefootprint for improved landingsperformance.

11

tread

protector ply

undertread

carcass pliesbelt plies

sidewall

bead linercarcass ply turn-ups

flipper strip

Radial Tire Construction

Single Chine Tire Dual Chine Tire

The chine tire is now in use asstandard equipment on manycommercial jets. It is fullyretreadable and may be used on any aircraft provided adequateclearance is available.

Chine tires

The “chine” tire is a nose wheel tiredesigned to deflect water and slushto the side and away from intakes onaft-fuselage mounted jet engines.

It consists of a flared upper sidewallprotrusion which deflects the spraypattern of water or slush displacedby the tire’s contact with the runway.A tire can have a single chine (onesidewall flared) for dual nose wheeltire configurations or double chines(both sidewalls flared) for singlenose wheel tire configurations.

Brandingcommercial bias tiretypical Michelin branding layout

12

1. AEA: Association of European Airlines

TRADEMARK

PART NO.

TUBELESS OR TUBE-TYPE DESIGNATION

QUALIFICATION STANDARD

LOAD RATING

MOLDED SKID

PLY RATING

SPEED RATING

EQUIPMENT IDENTIFICATION

AEA1 CODES

COUNTRY OF ORIGIN

SIZE DESIGNATION

For details, see page 17

SERIAL NUMBER CODE

13

Brandingcommercial radial tiretypical Michelin branding layout

1. DGAC: Direction Générale de l’Aviation Civile / 2. FAA: Federal Aviation Administration / 3. All MICHELIN aircraft radials are tubeless

TRADEMARK

MOLDED SKID

FAA2 QUALIFICATIONSTANDARD

COUNTRYOF ORIGIN

EQUIPMENT IDENTIFICATION

DGAC1

QUALIFICATIONSTANDARD

CONSTRUCTION DESIGNATION

SIZE DESIGNATION

PART NO.

TUBELESS3 DESIGNATION

SPEED RATING

TYPE NUMBER

LOAD RATING

PLY RATING

CODEIDENTIFICATION

For details, see page 17

SERIAL NUMBER CODE

Brandingmilitary bias tiretypical Michelin branding layout

14

1.SCD: Specification Control Drawing / 2.MS: Military Specification / 3.OEM: Original Equipment Manufacturer / 4. USAF: U.S. Air Force

TRADEMARK

EQUIPMENTIDENTIFICATION

QTR NO.

CUT LIMITS

COUNTRYOF ORIGIN

SCD1 NO. OR MS2 NO.OR OEM3

SPECIFICATION NO.OR USAF4 NO.

TUBELESS OR TUBE TYPE DESIGNATION

PART NO.

SIZE DESIGNATION

CODEIDENTIFICATION

NATIONAL OR NATOSTOCK NUMBER

For details, see page 17

SERIAL NUMBER CODE

Application is program dependant

MAXIMUM WEAR LIMIT INDICATOR

MW

L - 3

15

Brandingmilitary radial tiretypical Michelin branding layout

1. All MICHELIN aircraft radials are tubeless

TRADEMARK

INDEX LETTER

CODEIDENTIFICATION

COUNTRYOF ORIGIN

CONSTRUCTION DESIGNATION

SIZE DESIGNATION

TUBELESS DESIGNATION1 PART NO.

FABRICATIONMONTH / YEAR

TYPE NUMBER

For details, see page 17

SERIAL NUMBER CODE

MW

L - 3

Application is program dependant

MAXIMUM WEAR LIMIT INDICATOR

Brandingbias retread tire

16

Brandingradial retread tire

RETREADER TRADEMARK

TUBELESS DESIGNATION

AIRLINE CODE

PLANT CODE

SIZE DESIGNATION

PLY RATING

SPEED RATING

MOLDED SKID

MOLDED SKID

RATED SPEED

AEA TREAD CODE

MONTH &YEAR OFRETREAD

MONTH & YEAROF RETREAD

RETREAD R-LEVEL

CASING SERIALNUMBER

PLANT CODE

AEA TREAD CODE

RETREAD R-LEVEL

RETREAD CONSTRUCTION

DESIGNATION

AIRLINE CODE

INTERNAL MICHELIN CODE

MKC KANSAS CITY, USA

MNW NORWOOD, USA

MBO BOURGES, France

MCN CUNEO, Italie

MNK NONG KHAE, Thailand

17

Michelin tireserial number codes

Radial serial number definition:

Last number of the manufacturingyear (example: 9 for 1999).

3 numbers indicating themanufacturing day in Julian calendar(example: the tire was manufacturedthe 211th day of the year).

Code letter related to the facility andthe decade, see table below.

Unique production identificationnumber.

9 2 1 1 B 0 2 5

Bias Serial Number Definition:

Last number of the manufacturingyear (example: 9 for 1999).

3 numbers indicating themanufacturing day in Julian calendar(example: the tire was manufacturedthe 211th day of the year).

Code letter related to the facility andthe decade, see table below.

Unique production identificationnumber.

9 2 1 1 P 0 0 0 2 5

Letter signification

The letter code in the tire serial number is used to identify both the manufacturing facility and the decade of manufacture. It follows the rules below:

Manufacturing Through From Jan. 01, 1996 to from Jan. 01, 2000 to

Facility Dec. 31, 1995 Dec. 31, 1999 Dec. 31, 2009included included included

Bourges B B A

Clermont-Ferrand F F G

Greenville K K L

Nong Khae T T W

Norwood N P U

SSaaffeettyy

18 General safetyconsiderations

19

● Keep pressure hose and fittingsused for inflation in good condi-tion.

● Allow the tire to remain in theinflation cage for several minutesafter reaching full inflation pressure.

● Respect inflation pressures andall other safety instructions.

Tires in service

● Careful attention should beshown to tire/wheel assembliesbeing handled or in storage.

● Never approach a tire/wheelassembly mounted on an aircraft that has an obviousdamage until that tire has cooledto ambient temperatures (allowat least 3 hours).

● Always approach a tire/wheelassembly from an oblique angle,in the direction of the tire’sshoulder.

● Deflate tires before removingthem from the aircraft unless thetire /wheel assembly is to beimmediately remounted on theaircraft, such as with brake

inspections. Deflate tires beforeattempting to dismount the tirefrom the wheel or before disas-sembling any wheel component.Show caution when removingvalve cores as they can be pro-pelled at a high speed from thevalve stem.

● The transportation of a service-able aircraft tire/wheel assemblyshould be in accordance withthe applicable regulatory bodyfor the airline. Transportation of a serviceableinflated aircraft tire is covered bythe U.S. Department ofTransportation Code of FederalRegulations, the InternationalAir Transport Association (IATA),and other regulatory bodies.

● While serviceable tires may beshipped fully pressurized in thecargo area of an aircraft,Michelin’s preference is to reduce pressure to 25% of operating pressure or 3 bars / 40 psi, whichever is the lesser.

● Remove from service tire/wheelassemblies found with one ormore tie bolt nuts missing.

Aircraft tire and wheel assemblies mustoperate under high pressures in order tocarry the loads imposed on them.Theyshould be treated with the same respectthat any other high pressure vesselwould be given. Following therecommended procedures giventhroughout this manual,as well as thoseprovided by authorities such as wheelmanufacturers, air-framers andindustry regulatory agencies, willminimize the risks and chance of injury.

Mounting

Follow the instructions given in thesection on “General MountingInstructions For Aircraft Tires”. Be particularly attentive when:

● Rolling tires on the floor and usingmechanical lifting equipment toavoid possible back injuries.

● Inspecting tires and wheels inadvance for possible shippingdamage.

Inflating

● When inflating tires, be sure touse a suitable inflation cage.

IMPORTANT:In the event of aconflict between

recommended procedures, besure to contact your Michelinrepresentative

before undertaking

the procedure in question.

Angle of Approach

Recommended Angle of Approach

SSttoorraaggee

20 Storing aircraft tiresand tubes

Typical ozone cracking

Ozone cracking in groove

21

Tire can be lifted through center

through the center. Avoid the use offorks or other objects which havecorners that could damage the beadsurfaces. When possible, handle tiresby lifting or rolling.

Avoid moisture and ozone

Ozone - What is it ?

Ozone is a gas, a form of oxygen. Inthe earth’s atmosphere, where itoccurs naturally in small amounts,ozone plays a crucial geophysicalrole because of its intenseabsorption of solar ultravioletradiation. Additional ozone, createdwhen industrial exhaust mixes withultraviolet rays, can be harmful.Ozone degrades organic matter, suchas rubber.

Impact of ozone on tires

Most of the natural and syntheticelastomers used in aircraft tires aresusceptible to ozone attack.Ozone in the air readily reacts withthe double bonds (unsaturation) inthe rubber molecules. The result ofthis reaction is the breaking of

molecular bonds and a degradationof the rubber, which lead to crackinitiation. Continued stress, andespecially cyclic stress, causes thecrack to grow until it is visible as thecharacteristic surface crack,perpendicular to the direction of theapplied stress.

Designing for ozone

To aid in the control of ozone attackon rubber, the tire materials specialistadds waxes and protective chemicals.Some of these ingredients addressozone attack when the tire is in astatic state at room temperature;other ingredients are activated byheat and protect the tire once it is inservice. Further, the tire designer ismindful of the impact of shapes andcontours on stress concentrations.Still, steps need to be taken in storageto delay the effects of ozone attack.Wet or moist conditions have adeteriorating effect on tires andtubes, and can be even moredamaging when the moisturecontains foreign elements that arefurther harmful to rubber and cordfabric.

Tires are designed to be tough,durable and to withstand large loadsand high speeds. They can provideyears of reliable service if a fewprecautions are followed.The ideal location for tire and tubestorage is a cool, dry and reasonablydark location, free from air currentsand dirt.While low temperatures (not below 0°C/32°F) are not objectionable, roomtemperatures above 40°C / 104° F aredetrimental and should be avoided.

Handling aircraft tires

Care should be shown when hand-ling aircraft tires. While tough anddurable, tires can be damaged or cutby sharp objects or if excessive forceis used. Avoid lifting tires withconventional two prong forks ofmaterial handling trucks. Damage to bead mounting areas or theinnerliner can occur. A wide, flat,pincher type fork assembly of thetype that lifts the horizontal tire bysqueezing against the tread surfaceis recommended. An alternaterecommended method would be to use a rounded bar to lift the tire

Horizontal storage is not recommended

Strong air currents should beavoided, since they increase thesupply of oxygen and quite oftencarry ozone, both of which causerapid aging of rubber.Particular care should be taken tostore tires and tubes away fromfluorescent lights, electric motors,battery chargers, electric weldingequipment, electric generators andsimilar electrical devices, since theyall create ozone.

Store away from fuel and solvents

Make sure that tires do not comeinto contact with oil, gasoline, jetfuel, hydraulic fluids or otherhydrocarbon solvents, since all ofthese are natural enemies of rubberand cause it to disintegrate rapidly.Be especially careful not to stand orlay tires on floors that are coveredwith oil or grease. When working onengines or landing gears, tiresshould be covered so that oil doesnot drip on them.

If tires accidentally becomecontaminated, wash them off withdenatured alcohol and then with asoap and water solution. Aftercleaning, be sure to remove anywater that may have accumulated in the interior of an unmounted tire. If after cleaning, the surface of the tire appears soft, or spongy, or bulges are present, the tire is notsuitable for service. Should you haveany doubt about the serviceability of such a tire, please contact yourMichelin Representative orauthorized repair station.

Store in the dark

The storage room should be dark, or at least free from direct sunlight.Windows should be darkened with a coat of blue paint or covered withblack plastic. Either of these willprovide some diffused lightingduring the daytime. Black plastic is preferred since it will lower thetemperature in the room during thewarm months and permit tires to bestored closer to the window.

Fluorescent or mercury vapor lights should not be used because theygenerate ozone. Low intensitysodium vapor lights arerecommended. See the section on“Ozone” for more information.

Stores tires vertically

Whenever possible, tires should bestored in regular tire racks whichhold them up vertically. The surfaceof the tire rack on which the weightof the tire rests should be flat and, ifpossible, 3 to 4 inches / 7.5 to 10 cmwide to prevent permanentdistortion of the tire.

Horizontal stacking of tires is not recommended

If tires are stacked horizontally, theymay become distorted, resulting in mounting problems. This isparticularly true of tubeless tires.Those on the bottom of a stack mayhave the beads pressed so closelytogether that bead spreader toolswill have to be used to properlyspace the beads for contact with the wheel during initial inflation.

Store tires vertically in racks

Storing aircraft tires and tubes

22 Protect tires from contaminants

Tires which are stacked on top of each other, sidewall-to-sidewall,have increased stresses in the treadgrooves. If tires are stored for an extended period of time, or in an environment with high ozoneconcentration, ozone cracking is most likely to form in the treadgrooves.If tires must be stacked, they shouldnot be stacked for more than 6 months maximum. The maximumstacking height:

● 3 tires high if tire diameter isgreater than 40 inches / 1 meter.

● 4 tires high if tire diameter is lessthan 40 inches inches / 1 meter.

Store tubes properly

Michelin tubes should always bestored in their original cartons, sothey are protected from light and aircurrents. If stored without theircartons, they should be wrapped inseveral layers of heavy paper.Tubes can also be stored by inflatingslightly (not more than 0.06 bar / 1 psi)and inserting them in the same sizetire. This, of course, should only be

23

done as a temporary measure.Before mounting a tire and tubestored in such a manner, alwaysremove the tube from the tire andinspect the inside of the tire forforeign material, which, if notcleaned out, could cause irreparabledamage to both tube and tire.Under no circumstances shouldtubes ever be hung over nails orpegs, or over any other object whichmight form a crease in the tube.Such a crease will eventuallyproduce a crack in the rubber andcause tube failure.

Tire or tube age limit

Michelin aircraft tires or tubes haveno age limit and may be placed inservice, regardless of their age,provided all inspection criteria forservice/storage/mounting andindividual customer-imposedrestrictions are met.

Note: Certain regulatory agenciesrecommend further restrictingthe age of rubber productsused in the aircraft industry.The decision to adopt theserecommendations must bemade by the individual user.

Storage of inflated tire and wheel assemblies

Mounted tire/wheel assemblyproperly prepared and delivered to a line maintenance station as anairworthy replacement unit may bestored at full operational pressure for up to 12 months, see commentsin the section on tire mountingfound later in this manual.

OOzzoonnee

24 Aircraft tiresand ozone

25

Location:

● Inside a warehouse away from direct sunlight or precipitation. (Wet or moist conditions can carry other chemicals which can have a further damaging effect on tires.)

Storage Area Environment:

● Temperatures should remain between 0°C/32°F and 40°C/104°F.● Use reasonably low intensity lighting (sodium vapor lamps are preferred).● Environment should be free of strong air currents and excessive dirt.

Ozone Sources:

● Store away from fluorescent lighting, mercury vapor lamps, electric motors,battery chargers, electric welding equipment, and electric generators.

Tire Storage:

● Stand the tire such that it rests on its tread, whether on the floor or in a rack.● This orientation should be used for any tire which will be held in storage for

more than 1 months time. (Storage racks should provide an adequateamount of surface area to support the tire to prevent a distortion or “set”from occurring in the tread area).

● If high ozone concentrations can not be reduced or eliminated, each tireshould be protected by appropriate wrapping such as dark polyethylene or paper.

Mounted Tire:

● Mounted tires not immediately placed in service should be covered or wrapped until they are to be installed on an aircraft.

● To minimize the effects of ozone attack and where re-inflation capabilityexists, tire pressure may be reduced to a value below operational pressure,but not less than 25% of the operational pressure or 40 psi / 3 bars, whichever is less.

Recommendations for storage and handling

The following storage and handlingconditions are strongly recommendedto minimize the damaging effects of ozone:

GGeenneerraall mmoouunnttiinngg

26 General mounting instructionsfor aircraft tires

27

Premounting checklist

Wheels

Careful attention to details is neces-sary to successfully mount aircrafttires for trouble-free service. Makesure you are thoroughly familiarwith and inspect all key wheel partsbefore beginning to mount a tire.

To assist in this process, wheelmanufacturers publish specificinstructions in their maintenanceand overhaul manuals. Follow theirrecommendations and proceduresfor wheel assembly and disassemblyto obtain trouble-free mounting anddismounting.

Direct particular attention to the following:

● Ensure that the bead seatingarea of the wheel is clean anduncontaminated.

● Mating surfaces of the wheelhalves should be free of nicks,burrs, small dents, or otherdamage that could prevent thesurfaces from properly matingor sealing. Painted or coatedsurfaces should be in goodcondition; not badly chafed,chipped, etc.

● Be sure fuse plugs, inflation valves and wheel plugs are ingood condition, properly sealedagainst loss of pressure and correctly torqued per the manufacturer’s instructions.

● 0-Ring grooves in the wheelhalves should be checked for damage or other debris that would prevent the 0-Ringfrom properly seating.

General

Proper mounting procedures simplifythe job of servicing aircraft tires,while at the same time increasingsafety and reducing the chances ofdamaging tires or wheels.Do not mount aircraft tires withoutthe proper equipment, instructions,and operator training.

Be sure to know and understand allchemicals used on the tire and wheel.It is possible that under the highpressures and load exerted by the tireon the wheel, normally inert chemi-cals may contribute to rapid corro-sion and/or abrasion of the wheel, ordeterioration of the rubber surface.

Virtually all modern aircraft wheelsare of two types: split wheel type, i.e.,two “halves” joined by removable tiebolts, or the removable flange type.Both designs facilitate the mounting(and dismounting) of the tire. Showcareful attention in handling, assem-bling and disassembling wheel com-ponents to avoid damage to criticalsurfaces.

Wheel half and O-Ring

● O-Rings themselves must beof the proper material, asspecified by the wheel manufac-turer, for the intended applicationand temperature conditions.Inspect O-Rings for cracking,cuts, or other damage. Particularattention should be given to permanent deformations in the O-Ring. O-Rings found withdeformations should be replaced.Proper sealing of the wheel halves is critical in providingtrouble-free service.

● Should the inspection of aused O-Ring for its integritynot be practical or manageable,replace with a new O-Ring witheach tire change.

Tires

Before mounting any tire, verify thatthe tire is correct for the intendedapplication. Use the following checklist:

● Check that the tire markingsare correct for the requiredapplication (size, ply rating,speed rating, part number, TSOmarking).

● Visually inspect the outsideof the tire for:• Damage caused by improper

shipping or handling of the tire.• Cuts, tears or other foreign

objects penetrating the rubber.• Permanent deformations.• Debris or cuts on the bead

seating surfaces. Clean the tirebead surfaces with either aclean shop towel, a soap/watersolution, or with denaturedalcohol as may be necessary.

• Bead distortions.• Cracking that reaches cords.

• Contamination from foreignsubstances (oil, grease, brakefluid, etc.) which can causesurface damage (blisters orswelling).

● Inspect the inside of the tireto be sure there is no foreignmaterial present. Be sure thatthe inner liner condition is good,that is, without wrinkles. Checkfor liner damage caused byimproper shipping or handlingof the tire.

Refer to the section on “TireServiceability Criteria” for damages.If in question, tires should not beused and should be returned to acertified repair or retread station forfurther inspection and disposition.

28

WASHER

TIE BOLT

FIXTURE

INNER WHEELHALF ASSEMBLY

PACKING

OUTER WHEELHALF ASSEMBLY

Position Light SpotMay Be Stamped

On Wheel

PACKING

NUT

WASHER

TIREAircraft Tire/Wheel Assembly

General mounting instructionsfor aircraft tires

Mounting

Use of Inner Tubes

Bias TiresAll Michelin bias or cross ply tires,whether tube-type or tubeless, aresuitable for operation with tubesapproved for the particular tire sizeand application on tube-type wheels.

Radial TiresAll Michelin radial tires are oftubeless design. Never use an innertube or mount on a tube-type wheel.

Lubrication of Tire Beads

Bias TiresBecause of their typically wide beadflat, when installing bias tires onaluminum wheels, lubricate the toesof the beads with an approved 10%vegetable oil soap solution.

Do not use lubricant with magne-sium alloy wheels!

29

Lubricants manufactured from apetroleum base are not recommen-ded as hydrocarbons have a knowndetrimental effect on rubber compounds.

Radial TiresFor radial tires, use of a mountinglubricant is not specified, unlessapproved by the airframer.

Tire/Wheel Assembly

Again, be sure that the wheel, tire,and assembly components are ingood condition and free of debris.

Lubricate the O-Ring (as specifiedby the wheel manufacturer) andinstall in the wheel groove orchannel. Be sure the O-Ring is free ofkinks or twists.

Position the previously inspectedtire in front of the first wheel half. If a bias tire, lubricate the beads asrequired. Slide the tire on the wheel.

When mounting tube-type tires,dust the tube and the inside of thetire with tire talc or soapstone beforeinstalling the tube. This will preventthe tube from sticking to the insideof the tire or to the tire beads.Dusting also helps the tube assumeits normal shape inside the tireduring inflation, and lessens thechances of wrinkling or thinningfrom irregular stretching. (Caution:Use care not to damage tube whenmounting.)

To be consistent with the practice ofmounting the tire serial number tothe outboard wheel half, tubes shouldbe installed in the tire with the valveprojecting on the serial numberedside of the tire.

Assemble the two wheel halves,being sure to align the light point ofeach half 180° apart to insure theoptimum balance of the assembly.

When aligning the wheel halves, becareful not to damage the O-Ring inthe wheel base which seals the wheelhalves.

Tire/Wheel Alignment for Balance

The “red” balance mark on the lowersidewall indicates the light point ofthe tire’s balance. Align this mark withthe heavy point of the wheel. In the absence of a balance mark,align the tire’s Serial Number with the heavy point of the wheel (mainlanding gear position tires only).Many wheel manufacturers todayidentify either the light spot or heavyspot of the wheel with markings in theflange area. Follow their instructionson assembly and balance. Be sure toalign the tire’s light spot 180° from thewheel’s light spot or directly in linewith the wheel’s heavy spot. In theabsence of specific wheel markings,align the tire’s red balance mark withthe wheel inflation valve.Some aircraft tubes feature balancemarks to indicate the heavy portion ofthe tube. These marks areapproximately 1/2” wide and 2” long.When inserting the tube in the tire, itsbalance mark should be aligned withthe balance mark on the tire. If thetube has no balance mark, align the valve with the balance mark on the tire.

A properly balanced tire/wheelassembly improves the tire’s overallwear characteristics. In addition tosevere vibration, an unbalancedassembly will cause irregular andlocalized tread wear patterns thatcan reduce the overall performancelife of the tire.

Be sure that nuts, washers, and boltsare installed in proper order and thatthe bearing surfaces of these partsare properly lubricated as required.Tighten to manufacturer’srecommended torque values.

After the tire is mounted on thewheel, the assembly should beplaced in a safety cage for inflationwith nitrogen. It is recommendedthat the cage be placed against anoutside wall that is strong enough towithstand the effects of an explosionof either the tire, tube or wheel.

The inflation pressure source shouldbe located 10 meters / 30 feet awayfrom the safety cage with a valve,regulator and pressure gauge installed at that point. The inflationline should then be run to the safety

cage and attached to the wheelvalve. This arrangement allows thetire service person to inflate the tiresafely using the remote valve.

Inflating With Nitrogen

Many regulatory agencies require theuse of nitrogen when inflating tiresfor aircraft above a specifiedMaximum Take-Off Weight (MTOW).Michelin recommends the use of adry, commercial grade nitrogen of atleast 97% purity when inflating allaircraft tires. Nitrogen provides astable, inert inflation gas whileeliminating the introduction ofmoisture into the tire cavity.

Aircraft operating procedures forinitial inflation and adjustments mustcomply with applicable instructions asgiven in FAR 25 or JAR 25.

Oxygen concentration should neverexceed 5%.

30

General mounting instructionsfor aircraft tires

Tire balance mark

WARNING! Aircraft tires can be operated up to or at

rated inflation pressure;extremely high inflationpressures may cause theaircraft wheel or tire toexplode or burst, which

may result in serious or fatal bodily injury.

Aircraft tires mustalways be inflated with

a properly regulatedinflation canister.

The high pressure sideshould never be used.

The safety practices formounting and dismoun-

ting aircraft tires detai-led in this Manual must

be followed.

For safety: use a suitable metalinflation cage when inflatingtires.

Store the inflated tire/wheelassembly for 3 hours.Check inflation pressure:Be sure that the ambient temperature of the tire/wheelassembly has not changed by more than 3°C/5°F.Options:• If inflation pressure is equal to

or greater than (≥) 90% of thespecified operating pressure,proceed to Step 4.

• If inflation pressure is less than(<) 90% of the specified opera-ting pressure, inspect theassembly for leakage. Use asoap solution on tire beads andother susceptible wheel com-ponents (valves, fuse plugs,over-pressurization plugs,wheel half parting line, etc.). If soap bubbles or leaks arefound, make appropriaterepairs. Return to Step 1.

Re-inflate the tire to the speci-fied operating pressure.

4

3

2

Basic pressure retention check

Pressure retention checks are designedto verify that tire/wheel assembliesmeet industry standards for pressureretention prior to releasing them forservice on aircraft.This importantprocess assures reliable service andavoids costly returns for repairs.This basic pressure retention checkrequires approximately 15 hours todetermine if an assembly can beaccepted for service. Additionalchecks are performed on tire/wheelassemblies not meeting the minimumacceptance criteria for pressure loss.

To follow this procedure requires apressure gauge of 0.25% accuracy or better and capability to indicate 2 psi / .15 bar pressure change.

Procedure:

Inflate the newly mountedtire/wheel assembly to operatingpressure for the aircraft application as specified in shopinstruction manuals.

1

31

Special Procedure To ProperlySeat Tube-Type Tires

To seat tire beads properly on thewheel:

● Inflate the tire to the recommen-ded pressure for the aircraft onwhich it is to be mounted.

● Next, completely deflate the tire.● Finally, reinflate it to the correct

pressure (do not fasten the valveto the rim until this has beendone). Use a valve extension forinflation purposes if necessary.

This procedure helps remove anywrinkles in the tube and helpsprevent pinching the tube under thetoe of the bead. It eliminates thepossibility of one section of the tubestretching more than the rest andthinning out in that area. Further, itassists in the removal of air thatmight be trapped between the innertube and the tire.

Note: With tubeless tires, this inflation-deflation-reinflation procedure is not necessary.

Tire / Wheel Assembly

Inflate Tire to AircraftOperating Pressure PN

Check and Repair if Leakage

If PN < 90%

3 hours

Check Inflation Pressure

If PN ≥ 90%

Inflate Tire to AircraftOperating Pressure PN

If PN ≥ 97.5% Accept Assembly

Check Inflation Pressure

12 hours

If PN < 97.5%

Inflate Tire to AircraftOperating Pressure PN

If PN ≥ 97.5%

If PN < 97.5%

Accept Assembly

Repair or Reject

Check Inflation Pressure

24 hours

Basic Pressure Retention Procedure

After 12 hour storage period,check inflation pressure:Be sure that the ambient temperature of the tire/wheelassembly has not changed by more than 3°C/5°F.

Options:• If inflation pressure is equal to

or greater than (≥) 97.5% of thespecified operating pressure,accept the tire/wheel assem-bly for in-service usage or linemaintenance storage (seeStorage Section for recom-mendations on line mainte-nance storage).

Note: Re-inflate tire to thespecified operatingpressure.

• If inflation pressure is less than(<) 97.5% of operating pressure,inspect the assembly for leakage.Use a soap solution on tirebeads and other susceptiblewheel components (valves, fuseplugs, over-pressurization plugs,wheel half parting line, etc.).

5 If soap bubbles or leaks arefound, make appropriaterepairs. Proceed to step 6.

Re-inflate the tire to the specifiedoperating pressure.

After a 24 hour storage period,check inflation pressure. Be surethat the ambient temperature ofthe tire/wheel assembly has notchanged by more than 3°C/5°F.

Options:• If inflation pressure is equal to or

greater than (≥) 95% of the specified operating pressure,accept the tire/wheel assemblyfor in-service usage or line main-tenance storage (see StorageSection for recommendations online maintenance storage).

Note: Re-inflate tire to thespecified operating pressure.

• If inflation pressure is lessthan (<) 95% of operatingpressure, reject the tire/wheelassembly.

7

6

Alternate pressure retention check

This alternate, historical, procedure isdesigned to provide a more completecheck of tire/wheel assembly pressu-re retention prior to releasing themfor use on aircraft. The procedure is particularly beneficial when in-service pressure retention issueshave been encountered.

Procedure

● Allow for Tire GrowthNewly mounted tire/wheel assem-blies should stand for 12 hours toallow for normal tire growth (cordbody stretching) and to verify thatthe assembly is without leaks.After 12 hours, inspect the assem-bly carefully. Check the tire pres-sure drop. A 10% drop during tiregrowth is considered normal.More than that may indicate a lea-kage problem. Be sure that the tireassembly has remained at a cons-tant ambient temperature (±3°C/5°F). A drop of 3°C/5°F willreduce inflation pressure 1%.

32

General mounting instructionsfor aircraft tires

Tire / Wheel Assembly

Within 30 minutes

Inflate Tire to AircraftOperating Pressure PN

● If bubbles are found onwheel hardware or a stream of bubbles attire vents…

● If no bubbles are found atplugs, valves, “O-rings”, orno stream of bubbles attire vents…

Spray with leakdetection solution

Install Tire on Aircraft at Operating Pressure PN + 5% (unloaded)

Submitassembly for Basicpressurecheck

Check Inflation Pressurebefore each flight overthe next 48 hours

If PN ≥ 90% Accept Assembly

If PN < 90%

Remove the assembly(and mate) per theinflation pressuremaintenance schedule

Emergency pressure retention check:

The following proceduremay be used to perform a pressure retention checkon a newly mountedtire/wheel assembly whentime does not allow thebasic procedure to beapplied. Note this procedurerecommends a tire inflationcheck be performed beforeeach flight during the first48 hours after the assemblyhas been put into service.

Emergency Pressure Retention Procedure

● Check for LeakageAfter the growth period, reinflatethe tire to the specified operatingpressure. Recheck the pressureafter a 24-hour period. A pressureloss of 5% or less is considerednormal. Be sure that the ambienttemperature of the tire has notchanged by more than 3°C/5°F. Ifa greater than 5% pressure lossoccurs, investigate the tire/wheelassembly for leaks. Do not put thetire into service until the leaksource is identified and corrected.If the pressure loss is within theacceptable 5% limit, the assem-bly is now ready to be installedon the aircraft.Note that once in service, thetire/wheel assembly maximumdaily (24 hours) pressure loss is5%. Typical rates are 0.2-2.0% per 24-hour period.

Sidewall venting

Aircraft tires have traditionally beendesigned to permit any air or nitrogentrapped in the cord body or thatdiffuses through the liner or tube to

33

escape through special sidewall vents.Tires requiring vent holes have themplaced in the lower sidewall. Thisventing prevents pressure build-upwithin the carcass body which mightcause tread, sidewall, or plyseparations. The location of each vent hole on the new tire isindicated by a colored paint dot.Simply apply a soap solution tothese vent markings. Theappearance of small bubbles willindicate diffusion. This bubbling isnormal and may be seen at any timewhile the tire is inflated. Maximumallowable diffusion is 5% for any 24-hour period. Pressure losses inexcess of 5% may indicate leakagefrom other sources. In that case, thetire and wheel assembly should becarefully tested for leaks, preferablyby total immersion, before placing it into service. If no assembly leaksare found, dismount and have thetire inspected by the manufactureror a qualified repair shop.

Note: Do not identify a tire as a leaker solely on the rate ofbubbles from these ventholes. A high rate of bubbleventing is not always an indicator of tire leakage. It is best to judge excessiveleakage of a tire/wheel assem-bly based on pressure loss asmeasured with a calibrated gauge, preferablythe same gauge used toinitially inflate the tire.

Not all aircraft tires are vented

Improvements in materials, tire designand fabrication make the need forlower sidewall venting unnecessary forall aircraft tires. This is particularlytrue for the physically smaller tiressuch as General Aviation and HighPerformance Military tires.

Knowing which tires have beenvented is important. Tires requiringlower sidewall vents will have eithera green or white paint dot applied tothe area of each vent hole. Tires notneeding lower sidewall vents willhave no color dot in this zone.

Sidewall vent holes

Storage of an inflated tireand wheel assembly

Once a tire has been properly mountedand the assembly verified for pressureretention, only minimal precautionsneed be taken.

● Do not expose the tire to excessively high temperatures(greater than 40° / 104° F).

● Do not expose the tire todirect sunlight or to high ozoneconcentrations.

● Avoid contact with contaminants (oil, grease, etc.).

● A Mounted tire/wheelassembly properly preparedand delivered to a line mainte-nance station as an airworthyreplacement unit should meetthe following storage conditions:

• The pressure level should beset at operational pressure forthe tire application. Do notexceed operational pressure.

It is acceptable to STORE themounted assembly pressurizedin this range for up to12 months. After 12 months,any inflated assembly whichhas not been introduced intoservice should be returned tothe wheel mounting shop. The following inspections andactions should be taken withthe assembly before returningit to service. This storage andre-inspection interval can berepeated multiple times solong as the tire meets all criteria. However, to maximizetire life, it is recommended to rotate replacement stock.

Note: The conditions of storage, andthe tire’s response to thoseconditions, will determinewhether a stored, inflated tireis still airworthy. Time shouldnot be the measure by which atire is classified unserviceable.

• Shop re-inspection should bemade with the assembly infla-ted to the operational pressurelevel. The entire exterior of thetire should be visually inspec-ted for cracking (due to ozoneor ultraviolet attack), damages,or any other condition. If thelimits given in the chapter on“Tire Serviceability Criteria”have been exceeded, dismountthe tire from the wheel andreturn to the supplier.

Subject the assembly to thestandard air retention test toverify that the assembly willstill meet the criteria of nomore than 5% pressure loss ina 24 hour period.

While in storage, if the assembly inflation pressurewas being maintained usingcompressed air, deflate theassembly and re-inflate withnitrogen (per industry standards).

34

General mounting instructionsfor aircraft tires

Having met each of the aboveconditions, return thetire/wheel assembly to stock.

Note: The criteria for re-inspectionof the wheel must also bedetermined before returningthe assembly to service.

• To minimize the effects ofozone attack and where re-inflation capability exists, tirepressure may be reduced to avalue below operational pres-sure, but not less than 25% ofthe operational pressure or 40 psi / 3 bars, whichever is less.

● Transportation of a serviceable aircrafttire/wheel assembly should be in accordance with the applicable regulatory body for the airline.

Transportation of a serviceableinflated aircraft tire is covered by theU.S. Department of TransportationCode of Federal Regulations, the International Air TransportAssociation (IATA), and otherregulatory bodies.

While serviceable tires may beshipped fully pressurized in thecargo area of an aircraft, Michelin’srecommendation is to reducepressure to 25% of operatingpressure or 3 bars / ~40 psi,whichever is the lesser. Reinflate tooperating pressure before mountingon the aircraft.

35

MMoouunnttiinngg oonn aaiirrccrraafftt

36 Mounting tire/wheelassembly on the aircraft

37

Readjust Tire Pressure

Readjust Tire Pressure aftermounting the tire/wheel assemblyon the aircraft. Operating pressuresare set by the airframemanufacturers based on a variety offactors including maximum ramp ortaxi weight, center of gravity anddynamic loading. Reference theOperator’s Manual for the particular aircraft.

Important:

• Check pressure with aircraft loadon tire.

• Use loaded operating inflationpressure.

• Operational pressure values arefor loaded tires.

• Loaded inflation pressure = 104%unloaded inflation pressure.

Visually Inspect Tire/WheelAssembly

Visually Inspect Tire/WheelAssembly for damage fromhandling, storage, or contaminants. Look for deformations, bulges, swelling,blisters, or other anomalies thatwould make the assemblyunserviceable.

● Superficial cuts or cracks notreaching the cord body areacceptable for service.

● Groove cracking that does not reach the protector or reinforcing ply is acceptable for service.

Follow the guidelines given in this Manual for serviceability.

IInnffllaattiioonn pprreessssuurreemmaaiinntteennaannccee

38 Inflationpressure maintenance

39

Be particularly alert to severetemperature drops, which will alsoreduce tire pressure. Repeatedpressure losses beyond the daily 5%,under constant temperatureconditions, may signal a slow leak inthe tire/wheel assembly.

To avoid false readings, tire pressureshould be checked on “cool” tires(air in a hot tire will expand, causinga temporary higher pressurereading). Wait at least 3 hours afterlanding or until the tire has reachedambient temperature as noted bycarefully feeling with the palm of thehand, before making pressurechecks.

If it is absolutely necessary to checkpressures when tires are hot,compare the relative pressuresbetween tires on the same landinggear positions (main or nose). Neverbleed pressure from a hot tire [See“Checking Hot Tires” later in thissection for details].

Effects of Underinflation

Too little pressure can be harmful toyour tires and dangerous to youraircraft and those in it.Underinflated tires can creep or slipon the wheel under stress or whenbrakes are applied. Valve stems canbe damaged or sheared off and thetire, tube, or complete wheelassembly can be damaged ordestroyed. Excessive shoulder wearmay also be seen.

Underinflation can allow thesidewalls of the tire to be crushed bythe wheel’s rim flanges underlanding impact, or upon striking theedge of the runway whilemaneuvering. Tires may flex over thewheel flange, with the possibility ofdamage to the bead and lowersidewall areas. The result can be abruise, break or rupture of the cordbody. In any case where the bead orcord body of the tire is damaged, thetire is no longer safe to use and mustbe replaced.

Proper inflation - getting the most out of your tires

The most important service you canperform on your aircraft’s tires is tomake sure they are properly inflatedat all times. The more often you usethe aircraft, the more often the tiresneed checking. It is the Key toOptimum Service.

If you make one or more flights aday, tire pressure should be checkeddaily, with an accurate, calibratedgauge (preferably with a dial ordigital indicator appropriate for thepressure range of your tires). When installed, the TPIS (TirePressure Indicator System) can beused to make the daily inflationpressure check, provided the TPISindicators are verified against acalibrated pressure gauge at eachaircraft “A” check.

If you fly less than one time per day,you should check tire pressurebefore each flight.

Severe underinflation may cause plyseparation and carcass degradationbecause of the extreme heat, the strain caused by the excessiveflexing action, or the occurrence of premature standing waves (see photo). This same condition cancause inner tube chafing and aresultant blowout.

In dual tire applications,underinflation of one tire causes theother tire to carry a disproportionateamount of load. As a result, both tirescan be deflected considerably beyondtheir normal operating range,potentially causing ply separationsand/or carcass degradation.

Effects of Overinflation

Tires operating under too muchinflation pressure are moresusceptible to bruising, cuts andshock damage. Ride quality as wellas traction will be reduced.Continuous high pressure operationwill result in poor tire wearcharacteristics (center wear) andreduced landings performance.

WARNING! Aircraft tires can be ope-rated up to or at rated inflationpressure. Extremely high inflationpressures may cause the aircraftwheel or tire to explode or burst,which may result in serious or fatalbodily injury. Aircraft tires mustalways be inflated with a properlyregulated inflation canister. Thehigh pressure side should never beused. The safety practices for moun-ting and dismounting aircraft tiresdetailed in this Manual must be followed.

Checking Duals for EqualOperating Pressure

Tires mounted as duals or on thesame bogey, whether main or nose,whether bias or radial, should bemaintained at equal operatingpressure. If pressures are not equal,the tire with the highest pressure willbe carrying an unequal proportionof the load even though there maybe no perceptible differencebetween tire deflections. The graph on page 41 demonstrates this concept.

If it is determined that dual-mounted tires are operating atunequal pressures (more than 5% is cause for special attention), inflateboth tires to their proper pressure.Make a logbook entry indicating theoriginal pressure differential, thedate and time corrected and theambient temperature. At eachsubsequent pressure check, thelogbook should be consulted.

40

Inflationpressure maintenance

Standing Wave in Laboratory conditions.

If the same tire continues toevidence a pressure loss, it should bechecked for leakage (FOD, valvecore, etc.). If no obvious cause isfound, the tire should be removedand given a thorough inspectionuntil the reason for the pressure losscan be determined.

For mixability of bias and radialtires, see the section on “MatchingDual Tires” in this manual.

Proper Inflation - Setting thePressure Level

Inflating and Reinflating the Tire/Wheel Assembly

Whether for tubeless or tubetype,tire operating pressures should beset following the instructions givenby the airframe manufacturer. Fornewly mounted tires, follow theinstructions given in the section on“General Mounting Instructions ForAircraft Tires.”

Loaded versus Unloaded Tires

Be sure that it is clear whetheroperating inflation pressures aregiven for loaded or unloaded tireconditions. A tire’s inflation pressurewhen loaded will be 4% higher thanwhen unloaded (Loaded pressure =1.04 x unloaded pressure).

Properly Inflating Tube-Type Tires

Air is usually trapped between thetire and the tube at the time ofmounting. Although initial readingsindicate proper pressure, thetrapped air will seep out around thevalve stem hole in the wheel, andunder the beads. Within a few days,as the tube expands to fill the voidleft by the trapped air, the tire maybecome severely underinflated. Tocompensate for this effect, check tirepressure before each flight forseveral days after installation,adjusting as necessary, until the tiremaintains proper pressure.

41

60%

100%

100%

Pressure

Rated

100% pressure100% load

100% pressure100% load

200% Strut load

Def

lect

ion

Load BA120%80%

60% pressureA load

100% pressureB load

200% Strut load

Dual Tire Axle

Effects of Unequal Tire Pressure on Tire Loads

When required, reinflate tires totheir specified operating pressurewith a dry, commercial gradenitrogen of at least 97% purity.

In some cases, nitrogen may not beavailable for adjusting tire inflation.When this occurs, clean dry air maybe used as long as the oxygencontent does not exceed 5% of thetotal tire volume. If the 5% oxygenlimit is exceeded, the tire must bedeflated and then reinflated withnitrogen to the specified operatingpressure.

WARNING! In the event of excessiveheat build-up in the tire/wheelassembly (example, locked brakes),hydrocarbons released by the tiremay spontaneously ignite in thepresence of oxygen.A tire filled with air can explode,causing injury to persons anddamage to equipment.

Effect of ambient temperatureon gauge pressure

Effect of Temperature

Watch for severe changes in ambienttemperature. Changes intemperature affect gauge pressurereadings as follows:

1% change (increase) in inflationpressure reading for every 3°C/5°Fchange (increase) in temperature.

The above charts are a helpfulexample of the change in inflationpressure readings as a result of achange in ambient temperature. For convenience, it is given in metricunits and in customary units.

42

Inflationpressure maintenance

Metric Units

∆50 12.9 14.1 16.4 17.6

∆40 12.5 13.7 15.9 17.1

Temperature Rise °C ∆30 12.1 13.2 15.5 16.6

∆20 11.8 12.8 15.0 16.0

∆10 11.4 12.4 14.5 15.5

Specified Operating11 12 14 15

Pressure (bars)

∆10 10.6 11.6 13.5 14.5

∆20 10.2 11.2 13.0 14.0

Temperature Drop °C ∆30 9.9 10.8 12.5 13.4

∆40 9.5 10.3 12.1 12.9

∆50 9.1 9.9 11.6 12.4

Units in °C and Bars

Proper Inflation – Standard forMaintaining Pressure Level

A “cold” tire is defined as a tire whichhas come to equilibrium with itsoperating environment (ambienttemperature).

While the actual (ambient) temperatureof the “cold” tire will vary from locationto location and from season to season,the operational inflation pressure (PN),as specified by the airframemanufacturer for each aircraftconfiguration, is necessary to carry theload of the aircraft. This pressure valueis therefore needed regardless of theambient temperature. For example, if PN = 12 bars / 175 psi, this is the pressure needed at any ambienttemperature.

Note: Do not reduce the pressure of the “cold” tire subjected to frequent changes in ambient temperature.

[Refer to P. 44 for additional guidance.]

or● When pressure maintenance

is available at the destination airport, check and readjust to operating inflation pressure (PN)prior to the next flight.

In all other cases, maintain theinflation pressure per the standardrecommendation.

Aircraft experiencing largeambient temperaturedifferences between airports

Large temperature differences placea special burden on aircraftoperations. As can be seen in thechart above, large changes inambient temperature will result incorresponding changes in gaugepressure. Aircraft flying longdistances where a large (>30°C/54°F)decrease in ambient temperaturewill occur need to apply specificinflation maintenance procedures.One of two options should beselected in this situation:

● In the event that pressure main-tenance is not available at thedestination airport, raise the ope-rating inflation pressure (PN) by1% for each 5° F / 3° C temperaturedrop relative to the departure air-port to insure adequate inflationpressure in the assembly at the destination airport.

Note: Do not exceed maximumrated loaded tire pressure.

43

Customary Units

∆100 192 216 240 264

∆80 186 209 232 255

Temperature Rise °F ∆60 179 202 224 246

∆40 173 194 216 238

∆20 166 187 208 229

Specified Operating160 180 200 220

Pressure (bars)

∆20 154 173 192 211

∆40 147 166 184 202

Temperature Drop °F ∆6O 141 158 176 194

∆80 134 151 168 185

∆100 128 144 160 176

Units in °F and PSI

Schedule and action

Measured Pressure as % of Operating Tire Condition Course of ActionPressure

More than 105 Overinflated ● Because of variations in ambient temperature, gaugeaccuracy, etc., caution should always be shown beforeadjusting an overinflated pressure.

● It is recommended that the first overinflated reading berecorded in the aircraft log along with the ambienttemperature. After the 2nd confirmed reading >5%,readjust tire pressure to maximum of normal operatingrange.

105 -100 Normal Operating ● Do not adjust tire pressure.Pressure Range ● Do not exceed tire’s maximum rated pressure value

(loaded), nor the wheel’s TSO qualification pressure value (loaded).

100 - 95 Acceptable Daily ● Readjust tire pressure to maximum of normalPressure loss operating pressure range.

44

Inflationpressure maintenance

● Checking Hot Tires

Knowing if the pressure of a hottire is correct is nearly animpossible task. The air in a hottire expands, causing a temporaryhigher pressure reading. Theexact temperature is not knownand thus the relative pressure isalso unknown. As the tire cools,its pressure is also changing andwill continue to do so untilambient temperature is reached.

A hot tire is one that has dynamicallyrolled under load on the aircraft andhas not been allowed to reachambient temperature (not beenallowed to cool for at least threehours). Tires at elevatedtemperatures will develop inflationpressures higher than the specifiedcold inflation pressure.

Because of unusual circumstances, it may be necessary to check the pressure of a tire when it is hot.For example, check pressure if:

• tire shows excessive deflection

• flight schedules make itimpossible to make a routinepressure check on a cool tire

• tire is continually exposed todirect sunlight.

While no precise procedure can begiven for checking the pressure of ahot tire, the following instructionsand precautions should be followed.

When to Check

● Frequency

Tires in service should have their“cold” inflation pressure checkeddaily to properly maintainoperating pressures. For aircraftoperating on a less frequent basis,inflation pressure should bechecked before each flight.

When installed, the TPIS (TirePressure Indicator System) can beused to make the daily inflationpressure check , provided theTPIS indicators are verifiedagainst a calibrated pressuregauge at each aircraft “A” check.Understand that tires are capableof retaining pressure totolerances which will keep themwell within 5% of the specifiedpressure each day. Since pressurelosses due to other causes canseriously affect performance andsafety, it still remains arecommended practice to verifythe pressure value at least daily.

Continued on page 45

45

Schedule and action

Measured Pressure as % of Operating Tire Condition Course of ActionPressure

94 - 90 Accidental ● Readjust tire pressure to maximum of normalPressure Loss operating pressure range.

● Record in log book.

● Recheck pressure after 24 hours.

● If after 24 hours, pressure loss is again greater than the daily acceptable pressure loss (>5%), remove tire/wheel assembly.

● Inspect tire/wheel assembly for cause of pressure loss.

89 - 80 Pressure Loss ● Remove tire/wheel assembly from aircraft.

● Reinflate to specified operating pressure.

● If pressure loss is within daily acceptable pressure loss allowance (<=5%), accept assembly.

● If pressure loss is outside the daily acceptable pressureloss allowance (>5%), inspect tire/wheel assembly for cause of pressure loss.

● If the cause cannot be found, dismount tire for inspection by an authorized repair station.

79 - 0 Major Pressure Loss ● Remove the tire/wheel assembly.

● Remove the adjacent tire/wheel assembly.

● Replace tires*.

* If it is knownthat a majorpressure lossoccurred whilethe aircraft wasat rest or parkedand the wheelsdid not turnwith weight onthem, the tireand the adjacenttire can besaved. If doubtexists, tag thetire(s) and havean authorizedretread repairstation inspectthem.

• The basic rules to follow forcorrecting inflation pressure ofhot tires on the same landinggear:

● Single and Multiple tire gear -Should always be at least equalto, and may exceed, the specifiedoperating pressure.

● Two tire gear - If one tire is approximately equal intemperature but low in pressureit should be brought up to thepressure level of the other tire. In all cases, both tires should beat least equal to or greater thanthe specified operating pressure.

● Three or more tire gear -Check all tires on the gear. Any tire that is approximatelyequal in temperature but low inpressure should have its inflationincreased such that all tires arewithin a 5% pressure range. In all cases, all tires should be at least equal to or greater thanthe specified operating pressure.

Note: If one tire has an abnormallyhigh pressure (>5%) as compared to the other tires onthat gear, look for possiblecauses such as faulty brakes orincorrect pressure adjustmentat previous check.

Monitoring Inflation Pressure - What To Do

Checking and monitoring inflationpressure is usually performed onloaded tires. Be sure to knowwhether the operating inflationpressure is for loaded or unloadedtire conditions.

● Loaded inflation pressure is 1.04 xUnloaded inflation pressure.

● Use an accurate, calibratedgauge, preferably with a dial typeindicator.

● Watch for changes in ambienttemperature. A 3°C/5°Ftemperature change will result in a 1% tire pressure change.

● Compare tire pressures onthe same given landing gear

• Pressures measured from tireson the same landing gearshould be of the same magni-tude. They should always be at least equal to the specifiedoperating pressure.

• If any tire is less than 90% ofminimum loaded service pres-sure, remove the tire from ser-vice.

In such cases, note reason forremoval and return the tire toan authorized repair facilityfor examination.

• Aircraft flying between airportswith a significant temperaturedrop, should be aware of theeffects of temperature oninflation pressure. See section“Effects of Temperature.”

Do Not Reduce The Pressure of a Hot Tire.

Continued from page 44

● When making tire pressureentries in the aircraft log book, it is best to record the ambienttemperature along with thepressure readings.

● A recommended tracking systemfor daily pressure checks is towrite tire pressure, ambienttemperature and date on thesidewall of each tire duringpressure monitoring. Thismethod allows easy, quick follow-up on tire pressure conditionsfrom line station to line station.

● Make sure tires have sufficienttime to cool.

• A cool tire is one at ambienttemperature.

• Allow 3 hours after landing, if not exposed to direct sun-light, for tires to properly cool.By carefully using the palm of the hand, it is possible to determine if a tire is cool or not.

• Note that operating pressures,whether loaded or unloaded,are specified for “cool” tires.

• The maximum allowable pressure loss for a tire is 5%for any 24-hour period.

Pressure loss

Normal Response

The maximum daily pressure loss fora tire/wheel assembly is 5%.

The graph above shows how the normal pressure of a tire/wheelassembly can change with time evenwhen no disruption in the sealingsystem exists. It demonstrates the importance of checking pressurewhen mounting a new assembly on the aircraft.

180

80

160

60

40

20

00 10 20 30 40 50

1% loss rate

3% loss rate

Pressure loss more than 5% daily - reinflate to operating pressure

5% loss rate

60

140

120

100

Time (days)

Infl

atio

n Pr

essu

re (p

si)

46

Inflationpressure maintenance

Testing For Pressure Loss

The source of a pressure loss can bestbe determined by applying a soapsolution to suspected areas of leakageor by total immersion of the tire andwheel assembly in a water bath. Beginwith the most simple checks first:

● Check that the valve core is notleaking. Apply a small amount of soap solution on the end of the valve stem.If bubbles appear, replace thevalve core and recheck.Be sure that the valve stemthreads are not damaged.Otherwise, the valve core and thevalve cap will not fit properly.

Each valve should have a valvecap on it to prevent dirt, oil,moisture and other contaminantsfrom getting inside and damagingthe core.

● Be sure that the valve is not bentor rubbing against the wheel. Ifdamaged, dismount the tire andreplace the tube or valve.

● Check the fuse plugs or pressurerelief plugs with a soap and watersolution. If bubbles appear,replace the valve core andrecheck.

● Inspect the tread and sidewallareas for FOD’s, cuts, snags, etc.Check suspected areas with asoap solution. If bubbles appear,the tire must be dismounted andrepaired by a qualified repairstation or scrapped.

● Totally immerse the tire/wheelassembly in a water bath. If awater bath is not available, applya soap or other leak detectorsolution to the entire tire/wheelassembly. The appearance of bubbles at anypoint other than at the vents inthe lower sidewall of the tire justabove the wheel flange willindicate a leak.

47

Note that nitrogen will diffusethrough the sidewall vents for theentire life of an aircraft tire.

Look closely for bubbles in thetubewell area of the wheel to besure nitrogen is not leaking fromany fatigue cracks or at the O-Ring seal of the wheel halves.

● If no leak source other than the sidewall vents can be found, it will be necessary to dismount the tire and make a furtherinspection.

Causes of Pressure Losses

A tire that consistently loses inflationpressure beyond the 5% daily allo-wance should be inspected to determi-ne the cause of the pressure loss. Someinspections can be made while theassembly remains mounted on the aircraft. Others will require thetire/wheel assembly to be dismountedfrom the aircraft and sent to the tireshop. Follow the guidelines givenunder the section “MonitoringInflation Pressure - What To Do.”

There are a number of possible causesof pressure loss in a tire:

● Tire growth during the first 12 hours after mounting andinflation to the specified operatingpressure. This is entirely normal.

● To avoid a possible underinflationcondition, it is important that a tirenot be placed in service until it hasundergone the complete growthcycle and has been reinflated tothe specified operating pressure.

● An apparent pressure loss can becaused by a drop in ambienttemperature. Was the tireinflated in a heated room andstored in an unheated one? Wasthe tire relocated from a warmclimate to a cold climate? For moredetails on the effects of ambienttemperature, see page 42.

● Use only an approvedcalibrated gauge, preferably of adial or digital type. It is best to usethe same gauge when monitoringa slow pressure loss in a tire/wheelassembly.

● Foreign object damage thatpenetrates the cord body and liner.Inspect the tire carefully for anyFOD’s.

● Check for improperly seatedbeads. This condition can beidentified by comparing theposition of the tire’s lower sidewallannular rings, mold lines, orbranding. Look to see if they areuniform from side to side or thatthey are above the wheel flange.

This condition can be caused by:• Insufficient inflation pressure.• Bead toes (bias tires only) not

properly lubricated.• Kinked or distorted beads.• Accumulation of rubber on the

bead flats.• Dirt trapped between the tire

and wheel.

48

Inflationpressure maintenance

● Leaks at the valve stem or valve core.- Put a small amount of water

on the end of the valve stem and watch for bubbles. If bubbles appear, replace the core and repeat the check.

- Valve caps, finger tightened,should be used to prevent dirtfrom entering and holding openthe valve stem.

● Leaks at the valve seal(tubeless tires).- Valve holes in the wheel must

be free from scratches, gougesand foreign material.

- The proper O-Ring or grommet,as specified by the wheelmanufacturer, must be used.

● Wheel half parting line O-ringseal (tubeless tires) leaks inservice.

• Twisting or failure to lubricatethe O-ring before installationmay cause leakage at thewheel mating surfaces.

• Use of the wrong O-Ring com-pound, as specified by the

● Seepage between tire beadand wheel flange (tubelesstires) can occur. An inspectionshould be made with particularattention to the following:

• Look for exposure of cord bodyin the bead toe area or beadflat area. Exposed cords mayact as a wick for nitrogen toescape along.

• Foreign material trapped bet-ween the bead and wheel sea-ling surfaces causing a poorsealing between the tire andwheel.

• Gouges or scratches resultingfrom handling or improper useof tire irons. Damage can alsooccur along the wheel halfmating surfaces and leakagemay show in the O-ring sealarea.

• Corrosion or wear in the beadledge area (usually toe area ofthe tire bead) will leak at thetire-wheel contact area.

49

wheel manufacturer, suitablefor the intended aircraft service(in particular low temperatureservice) may also cause leakageat the wheel mating surfaces.

• This type of leakage is very dif-ficult to diagnose since the in-service conditions causing theleakage are not reproducible ina shop.

● Leakage through the fuse plug(tubeless tires).

• Use sealing gaskets specifiedby the wheel manufacturer,suitable for the intended aircraft service (in particularfor low temperature service).

• A faulty fuse plug can allow aseepage of nitrogen and thus aloss of pressure.

● Pressure release plug (tubelesstires). Some wheel designs have apressure release plug. Thepotential causes of leakage arethe same as for a fuse plug.

• A tube-type wheel convertedto tubeless application shouldhave the knurls removed.Leakage will show at the tire-wheel contact area.

● Leakage through the wellarea of the wheel (tubeless tires)can occur from porosity or fatiguecracks, particularly if fatigue life isexceeded. Proper painting of thewheel should seal leakage fromminor porosity.

● Damaged Wheel SealingSurfaces or improperlymachined sealing surfaces maycause slow leakage. Correctirregularities before assemblingthe wheel. Foreign material orheavy paint can impair thesealing surface.

● Damage to the tire innerliner(tubeless tires).

● Small cracks or splits in theinner tube.

For a Mounted For a DismountedIn all cases,Tire/Wheel Assembly,

For a Dismountedbe sure

Assembly, check tireAssembly,

to account for:check for: and tube for:

check wheel for:

Initial Stretch Period(24 Hour Tire Growth)

X

Changes In Air Temperature XVenting of Tubeless Tires X XRelease of Trapped Air in Tube-Type Tires X X

Cut or Puncture X XDamaged Beads XImproperly Seated Beads XLeaking Valve core XOther Valve Problems X XImproper Installation of O-Rings XFaulty Thermal Fuse or Installation X XPorous Wheels X XImproperly Torqued Wheel Tie Bolts XWheel Gouges and Scratches X XCorrosion or Wear on Bead Ledge Area XKnurls XDamaged Sealing Surfaces X XWheel Assembly Holes XWheel Cracks X X50

Inflationpressure maintenance

Troubleshooting - Have You Considered?

The above pressure loss troubleshoo-ting chart for tire/wheel assemblieswill help you set up a uniforminspection procedure which can pre-vent problems and speed troubles-hooting. Determine the status ofyour assembly in the columns above.

Note:• Tire inflation pressure must be

at operating or rated pressurewhen testing for points of pres-sure loss.

• The point of leakage can bedetermined for the tire wheelassembly by applying a soapand water solution to the entireassembly or by immersing thetire/wheel assembly in water.

SSeerrvviicceeaabbiilliittyyccrriitteerriiaa

51Tire serviceability criteria

A simple, easy-to-perform series ofinspection procedures can preventminor incidents from developing intomajor problems and help to optimizetire performance. Regular inspectionis a small price to pay to protect yourvaluable tires, and the safety of youraircraft and the people it carries.

Note: If an aircraft has made anemergency or particularlyrough landing, the tire, tubeand wheel should always be checked.

On-aircraft inspection withtire mounted

Removal Criteria - Wear

The tread area of the tire should bevisually inspected for any damageand the state of tread wear. Removalat the right time will optimize tirewear, while still protecting the lifeand investment of the carcass.In the absence of specificinstructions from the Airframer(Operations Manual, ServiceBulletins, etc.), a tire should

be removed from service for wearusing the following criteria:

Based on the fastest wearinglocation, remove tires:

● When the wear level reaches thebottom of any groove along morethan 1/8 of the circumference onany part of the tread,

or

● If either the protector ply (radial)or the reinforcing ply (bias) isexposed for more than 1/8 of thecircumference at a given location.

Note: Tires reaching this wear pointon an aircraft at a remote station can make a return-to-base flight(s) under standardoperating conditions withoutsacrificing retreadability of thecasing.

Note: In some military applications,the removal point of a tire is indicated by a red fabriccord built into the tire or a wear depth plug.

Water can affect traction:

The accumulation of water onrunway surfaces can affect wettraction. Its affect is dependent on a number of factors including waterdepth, aircraft speed and runwaysurface conditions. The mosteffective method to minimize the affects of water on traction is to reduce water depth or allow the water to escape from under the footprint more rapidly. Manyairport authorities today haveadopted “cross-grooving” for theirrunway surfaces which allows for rapid drainage of water.

Tire serviceability criteria

52

Tread Reinforcing plies

Casing Outer PlyBelt Plies Casing Outer PlyProtector Ply

Wear Removal Criteria for Retreadable Bias Tire Wear Removal Criteria for Retreadable Radial Tire

Typical Wear Conditions:

● Normal wearWhen tire wear has beenoptimized from propermaintenance and inflationpressures, the first point ofwearout will be near thecenterline of the tire. Follow wear removal criteria.

● OverinflationWhen a tire has been operatedwith a higher pressure than required for the aircraftloads, an accentuated centerlinewear will be apparent.Overinflation has reduced thenumber of cycles to wearout andmade the tire more susceptible to bruises, cutting and shockdamage. Follow wear removalcriteria.

53

Belt Plies Casing Outer PlyProtector Ply Belt Plies Casing Outer PlyProtector Ply

Normal Wear Patterns - Radial Tire Effects of Overinflation - Radial Tire

Tread Reinforcing plies

Casing Outer Ply

Tread Reinforcing plies

Casing Outer Ply

Normal Wear Patterns - Bias Tire Effects of Overinflation - Bias Tire

● UnderinflationWhen a tire has consistently beenoperated underinflated, shoulderwear will result. Severeunderinflation may cause plyseparations and carcass heatbuild-up which can lead tothrown treads, sidewall fatigueand shorten tire life. Follow wearremoval criteria.

Tire serviceability criteria

54

Belt Plies Casing Outer PlyProtector Ply

Effects of Underinflation - Radial Tire

Tread Reinforcing plies

Casing Outer Ply

Effects of Underinflation - Bias Tire

Tread Reinforcing plies

Casing Outer Ply

Belt Plies Casing Protector Ply

● Worn Beyond RecommendedLimitsTire has been worn beyondacceptable limits and into the topbelt plies (top carcass plies forbias - not shown). Tire is notretreadable.

● Flat SpottingThis tire wear condition is a resultof the tire skidding withoutrotating, i.e., brake lockup orlarge steer angle.

• Tire should be removed fromservice if the flat spottingexposes the protector ply(radial tire) or reinforcing ply(bias tire).

• If flat spotting does not extendto the protector ply or reinfor-cing ply, the tire can be left inservice.

• If the localized loss of rubberresults in aircraft vibrations,even though no fabric hasbeen exposed, the tire must beremoved from service.

● Asymmetrical WearThe tire has been operated underprolonged yaw and/or camber. This camber angle can beinduced through landing gear orundercarriage deformation ormanufacturer’ssettings/tolerances. Taxiing withone engine or high speedcornering can also causeasymmetrical wear.In some cases, low inflationpressure will contribute to thiscondition. Tires that do notexpose any fabric can bedismounted, turned around andremounted to even up wear. As long as standard wear criteria is met, the tire should remain in service.

55

Belt Plies Casing Outer PlyProtector Ply

Asymmetrical Wear - Radial Tire

Tire Flat Spot - Bias Tire

Outer Ply

Worn Beyond Limits -Radial Tire

● Serviceability Criteria/ LimitsFor Tire DamagesWhen assessing tire damages, it isbest to make inspections with thetire inflated. Many damages thatare readily visible on an inflatedtire can no longer be seen whenthat tire is uninflated.

Be sure to mark all damages witha chalk stick before dismountingthe tire.

Tires removed should be taggedwith a “Reason For Removal.”

A Systematic Approach to TireInspection assures that all parts of the tire are properly inspected. A recommended sequence ofinspection is given above:

● Tread wear* Check for typical wear patterns.

Follow removal guidelines givenunder the section “RemovalCriteria - Wear.”

Tire serviceability criteria

56

2

4

3

1

Suggestedapproach:1.Tread2.Sidewalls3.Bead areas4.Innerliner

● Tread Cuts/Foreign ObjectsTread cut removal limits are attimes given in specificdocumentation such as aircraftmaintenance manuals, T.O.4T-1-3, technical documentation,airline operation manuals, tiresidewall markings, etc. Followspecific guidelines when given.

In the absence of specific cutremoval documentation, tiresshould be removed when:

• Cuts, embedded objects orother injuries expose or pene-trate the casing cord body (bias)or tread belt layers (radial).

• If a cut or injury severs orextends across a tread rib, thetire should be removed fromservice.

• Under cutting at the base of any tread rib cut is cause for removal.Round foreign object openingsare acceptable up to 9.5 mm/0.375” in diameter.

Note: Tires removed for tread cutsor other injuries should besent to a certified repair station to be repaired andretreaded or scrapped.

57

Tread CutsRemove tirefrom servicewhen:A. Depth of cut

exposes thecasing outerply (bias) orouter beltlayer (radial).

B. A tread ribhas beensevered.

C. Undercuttingoccurs at the base of any cut.

Belt Plies Casing Outer PlyProtector Ply

B

AC

Radial Tire

Tread Reinforcing plies

Casing Outer Ply

B

AC

Bias Tire

Embedded objects take all forms

Mark all cuts, foreign objects,damages or leaks while tire isinflated. Use a light coloredcrayon, wax marker or paint stick.Damages can be difficult to find when a tire is uninflated.

Caution: Do not probe objects whiletire is inflated.

Bulges or separations Immediately remove the tire fromservice. Mark these areas with acolor crayon before deflating.

Tire serviceability criteria

58

Tread Reinforcing plies

Casing Outer Ply

Bulge

Separations Bias Tire

Chevron CuttingRemove from service if thechevron cutting results inchunking which extends to andexposes the reinforcing orprotector ply more than 6 cm2 /1.0 sq. in.

Tread Chipping/ChunkingRemove from service if thereinforcing ply (bias) or protectorply (radial) is exposed for morethan 6 cm2 / 1.0 sq. in.

59

Chevron Cutting:Remove tire from aircraft if:• Cutting causes

the tread toloosen or chunkexposing thetreadreinforcing plyor protector plymore than6 cm2 / 1 in2

Continue in service if:• Cutting

penetrates thetread to a levelless than one-half the moldedskid depth even if the surfaceexhibits someshallowchipping orchunking.

Tread Reinforcing plies

Casing Outer Ply

Chevron Cutting - Bias Tire

Belt Plies Casing Outer PlyProtector Ply

Tread Chipping / Chunking - Radial Tire

Chevron Cutting not exposing textile can be left in service

Peeled RibRemove from service if thereinforcing ply (bias) or protectorply (radial) is exposed.

Groove CrackingRemove from service if the groovecracking exposes the reinforcingply or the protector ply for morethan 6 mm/1/4” in length.

Note: Authorization is given to return to maintenance base(<6 flights) to replace tiresmeeting the above criteria if there is no continuous cracking exposing textile greater than 25 mm / 1 inch in length.

Rib UndercuttingRemove from service ifundercutting extends more than6 mm / 1/4” under the rib.

Contamination From HydrocarbonsOil, grease, brake fluids, solvents,etc. can soften or deterioraterubber components.Immediately upon contact with ahydrocarbon substance, wash thecontaminated area first withdenatured alcohol, then with asoap and water solution. Bypressing the rubber surface in thecontaminated area versus theadjoining uncontaminated area,determine whether the rubberhas become softened or “spongy”.If so, remove the tire from service.

Tread Reinforcing plies

Casing Outer Ply

Cracking and Contamination - Bias Tire

Tread Reinforcing plies

Casing Outer Ply

Peeled Rib - Bias Tire

Tire serviceability criteria

60

Skid Burns from HydroplaningThis condition occurs on wet or ice-covered runways. Removefrom service if the reinforcing plyor the protector ply is exposed.orif the severity of any flat spot issuch that aircraft vibration isunacceptable to operationalcrews.

Rubber reversion visible on the surface does not affect the performance capability of the underlying tread rubber andshould not be the determiningfactor for removal.

Open Tread SpliceRemove from service if apparent.

61

Belt Plies Casing Outer PlyProtector Ply

Tread Splice - Radial Tire

Belt Plies

Abrasion & Reverted Rubber

Casing Outer PlyProtector Ply

Skid Burn - Radial Tire

● Sidewall Cuts/Foreign ObjectsCuts, Snags, Gouges or OtherInjuriesMark all damaged areas with alight colored crayon, wax markeror paint stick while the tire isinflated. Such injuries can bedifficult to find when the tire isuninflated.

Caution: Do not probe cuts whiletire is inflated.

• If sidewall cords are exposed or damaged, remove the tire from service.

• Cuts in the rubber which do notreach the cord plies are not detrimental to tire performance.The tire can be left in service.

• Chine tires: Any cut that severs or extends across the chine and is more than 1/2 the depth of thechine should be removed.

Sidewall Bulge/Blister/SeparationIf any are found, the tire shouldbe removed from serviceimmediately.

Sidewall Cut or Crack● If condition is within the

sidewall rubber, continue inservice.

● If sidewall cords are exposed ordamaged, remove the tire fromservice.

Bulge / Blister / Separation Remove the tire from service.

Weather / Ozone CrackingRemove from service only if weather or ozone checking or cracking extends to the cords.

Important: Weather checking orcracks that do not reach the carcasscords are not detrimental to tire performance and do not constitutecause for removal. Tires showingonly surface cracking can be left in service.

Tire serviceability criteria

62Sidewall Bulge

Tire Cut

Typical Ozone cracking

Extends across chine

>1/2 depth of chine

Chine damage

Serviceability Criteria /Operational Conditions:

● Hard LandingAfter a particularly hard landing,tires, wheels, brakes and landinggear systems should be visuallyinspected for damage.

Inspect the tires for any obvioussigns of damage such as cuts,splits in the rubber, flat spotting,tread chunking, bulges, etc. Fordamages, follow the guidelinesgiven under Serviceability Criteria / Limits For Tire Damages.

If no damages are noted, thetire(s) should be left in service.

It is recommended that an entryof the landing be made in theaircraft log as a future reference.Some tire damages, such asbottoming the tire, may notbecome apparent until severallandings later.

● Rejected Take offAircraft experience various levelsof rejected takeoffs. Not allrejected takeoffs are severeenough to warrant automatic tireremoval. The following guidelinesare recommended:

• Where aircraft speed remainsbelow normal landing speedsand normal braking energiesare experienced, tires may beleft in service. A visual inspec-tion should be made on eachtire to assure all tires meet theserviceability criteria. Pay par-ticular attention to any tire flatspotting that may have occur-red as a result of braking. A minimum 30 minute tire /brake cooling period is requi-red prior to the continuationof the aircraft’s flight schedule.

63

• Where aircraft speeds exceednormal landing speeds andhigh braking energies areexperienced, tires should beremoved from service, labeledas an RTO tire and returned tothe retreader for inspectionand disposition.

Off-Aircraft InspectionWith Tire Dismounted

A Systematic Approach to Tire Inspection

A systematic approach to tireinspection is recommended toinsure that all areas are properlyinspected. The following system isrecommended.

Inspect the Tread Area.Follow the procedures given for On-Aircraft Inspections.

After the tread area, Inspect Both Sidewall Areas.Follow the procedures given for On-Aircraft Inspections.

Inspect the Bead Areas.

● Check the entire bead area fromjust above the heel of the beadto the innerliner for chafingfrom the wheel flange ordamage from tire tools.

● For Bias Tires:

• An exposed chafer strip on thebead face will normally causeno trouble and such a tire is fitfor service and can be retrea-ded.

• Damage, blisters or separa-tions of the chafer strips arerepairable. Send the tire to an authorized repair station.

• If carcass cords under chaferstrip are damaged, the tireshould be discarded.

● For Radial Tires:

• If bead area wear, along thewheel flange, exceeds1 mm/1/32”, remove the tirefrom service.

• If protruding bead wires, beadwire separations, or badly kin-ked beads are found, the tireshould be discarded.

Inspect the Tire’s Innerliner.

● As with external areas, any tirewith loose, frayed or brokencords inside should bediscarded.

● Liner blisters, especially intubeless tires, should be leftundisturbed. Do not pierce,puncture or cut them. To do sowill destroy the air-retainingability of a tubeless tire.

● Generally, confirm the goodcondition of the innerliner (e.g., no wrinkles).

Tube Inspection.

● When inspecting tubes, do notinflate them with more pressurethan is required to simply roundout the inner circumference ofthe tube (never more than 1 psi).

● Carefully inspect the inflatedtube for leaks. First visually andthen by submersion in water.

Tire serviceability criteria

64

● Examine the valve stem forleaks, signs of valve padseparation and bent ordamaged valve stems.

● Inspect the tube for severewrinkles or creases. Removefrom service if any are found.Wrinkles are evidence ofimproper fitting of the tubewithin the tire. Where wrinklesexist, chafing takes place, andthat can result in loss of air or ablowout.

● Inspect tubes for evidence ofchafing by the toes of the tirebeads. If chafing exists, removethe tube from service and scrap.

● Examine for thinning. Wherethe heat is greatest, the tubehas a tendency to be stretchedover the rounded edge of thebead-seat of the wheel. This isone of the reasons why, whenmounting, tubes should alwaysbe inflated until the tire beadsare in position, then completelydeflated and reinflated to the final pressure.

65

The stretch on the tube is thenequalized throughout its innerand outer periphery.

Also check tubes for possiblethinning out due to brake drumheat in the area where they contactthe wheel and bead toes. The “set”or shape of the tube will help todetermine when it should beremoved from service because ofthinning in the bead areas. Feelingthe tube with the fingers will alsoreveal thinned areas.On wheels with only one brakedrum, this heat-set condition willnormally show up only on one sideof the tube. In those cases wherethe brake drum is a considerabledistance from the rim, it is unlikelythat this condition will ever beexperienced.

Inspect For Wheel Damage.

● Wheels should be inspectedfollowing the wheelmanufacturer’srecommendations.

● In general, make a visualinspection of the entire wheel.Wheels that are cracked ordamaged should be immediatelytaken out of service for furtherchecking, repair or replacement.

● If used, check the condition ofthe thermal fuse plug oroverinflation plug. Melted,pushed out or leaking plugsshould be replaced. Be sure thatsealing gaskets are the onesspecified by the wheelmanufacturer for the serviceconditions of the aircraft.Gaskets should be free fromdistortion and damage.If a fuse plug blows while the tireis rolling, the tire and itsaxlemate should be scrappedbecause both tire will have beensubjected to overload conditions.

MMaattcchhiinngg //MMiixxaabbiilliittyy

66 Matching and mixabilityof dual tires

67

Mixability

The mixability of aircraft tires hasbecome an important issue in recentyears. It is Michelin’s position thatthe ultimate authority for approvingmixability of different tires on anaircraft lies with the aircraftmanufacturer or aircraft designauthority who alone has fullknowledge of all aircraftperformance requirements.

A key point for mixability is thatmatched tires carry the same load at the same pressure. Three possible configurations of tires exist. Thefollowing guidelines are given formixability:

● Bias - Bias• Bias tires can be mixed on the

same axle or bogie if the follo-wing requirements are met:� The tires are of the same size

designation.� All tires are qualified for the

aircraft application.� All tires meet the type

designation and overall

Matching Tires

In applications involving dual wheelsor dual wheels on a multi-wheellanding gear configuration, tiresshould be matched in diameter or static loaded radius within the appropriate association’s (T&RA,ETRTO, MIL-T-5041, AIR 8505A, etc.)inflated dimensions for both new and grown tires. It is important to ensure equal distribution of aircraftload on all tires and to avoid over-loading a tire beyond its limits.

Matching Criteria

Matching tires assures that the sizingof the tires is such that both tires willcarry, within industry standards,equal loads.

● Bias tires: • Same Size• Same Type• Within the Overall Diameter

limits as recommended by thegoverning association for theparticular application (civil,military).

● Radial tires: • Same Size• Same Type• Within the same Static Loaded

Radius limits:

� For Civil application Radialtires, use grown dimensions.REFERENCES:- “Tire and Rim Association

inflated dimensions.”- “Michelin Aircraft Tire

Engineering Databook.”

� For military applicationRadial tires, use inflateddimensions.REFERENCE:- “Michelin Aircraft Tire

Engineering Databook.”

● New versus Retreaded tiresThe practice of mounting bothnew and retreaded tires on thesame axle is acceptable. Followthe same guidelines as above.

diameter size standard established by either:- The Tire and Rim Associationor- The European Tyre and Rim

Technical Organization

● Radial - Radial• Radial tires can be mixed on

the same axle or bogie if thefollowing requirements aremet:� The tires are of the same size

designation.� All tires are qualified for the

aircraft application.� All tires meet the size

standards for overall diame-ter and static loaded radiusestablished by either:- The Tire and Rim Associationor- The European Tyre and Rim

Technical Organization.

● Bias - Radial• No specific rule can be applied

for this case. The mixability ofbias and radial tires is determi-ned by the airframer through

aircraft testing. In all cases,airframer and airworthinessauthorities recommendationsmust be followed.

Three possibilities exist:

Bias tires on the nose gearand Radial tires on themain gear or vice versa.- No effect on tire or aircraft

performance unless otherwise specified by the airframer.

Mixing on a gear made upof bogies and dual mounts.- Any proposed mixing

must be approved by theairframer.

- Radial and Bias tiresapproved for the sameapplication may be of dif-ferent overall diameterswhen stood side by side. Itis important that the staticloaded radius of the twotires be the same (see figure above). Contact the airframe manufacturer ortire manufacturer for static

2

1

loaded radius information.- Radial tires approved for

application on the sameaxle or bogie of an aircraftwill operate at the sameinflation pressure.

Bias tires on one main lan-ding gear bogie and Radialtires on the other.

- Any proposed mixing must be approved by the airframer.

- Radial and Bias tires approved for the sameapplication may be of different overall diameterswhen stood side by side. It is important that the static loaded radius of the two tires be the same.

- Radial tires approved forapplication on the same aircraft but different axles or bogies may operate at different inflation pressu-res than the Bias tire. This is mostly true of highperformance military applications.

3

68

Matching and mixabilityof dual tires

OD1

SLR1

OD2

SLR2

SLR1 = SLR2 - OD1 ≠ OD2

Observe Load and InflationRecommendations

When operating tires incombination, it is important to respect load and inflationrecommendations.

There is a limit to the load anyaircraft tire can safely carry. The maximum static load limits, as recommended by the Tire and Rim Association and/or the European Tyre and RimTechnical Organization, are shownin the Load and Inflation Tables in the document entitled MichelinAircraft Tire Engineering Data.Similar information is also containedin the T&RA Yearbook and ETRTO Data Book.

Overloading a tire puts undue strainon the cord body and beads of thetire, reducing its safety factor andservice life.It further increases the chance ofbruising, impact and flex breaks inthe sidewall or shoulder areas of thetire, particularly under landing stress

WARNING! Aircraft tires can be operated up to or at rated inflationpressure. Extremely high inflationpressures may cause the aircraftwheel or tire to explode or burst,which may result in serious or fatalbodily injury. Aircraft tires mustalways be inflated with a properlyregulated inflation bottle or canister.The high pressure side should neverbe used. The safety practices formounting and dismounting aircraft tires detailed in this Manualmust be followed.

or in the event the tire strikes anobstruction. It can cause potentialwheel damage. Under the severestrain of an extra load, the wheelmay fail even before the tire does.

It is important to use inflationpressures recommended by theairframe manufacturer for each tire.Be sure to determine if loaded orunloaded inflation pressure isspecified. Loaded inflation pressurewill be 4% greater than unloadedinflation pressure.

If tires are run at unequal pressures,the tire with the higher inflationpressure will carry a greater share of the load even though both tireswill be of the same deflection. This higher shared load can reducethe safety factor and service life of the tire.

Tire pressures should be checkeddaily with an accurate gauge whenthe aircraft is engaged in more than one flight a day. Otherwise,pressures should be checked before each flight.

69

VViibbrraattiioonn // BBaallaannccee

70 Vibration andbalance

71

generally work any trapped airout from between the tubeand tire.

● Is the tube wrinkled becauseof improper inflation procedures?

● Is the wheel out of balancebecause of improper assembly?• Follow the wheel manufactu-

rer’s instructions for properlyaligning wheel halves.

• The balance mark on the tireshould be aligned with thevalve mounted on the wheel,unless otherwise specified bythe wheel manufacturer.

● Check the condition of thewheel to see if it has been bent.

● Check for a loose wheelbearing caused by animproperly torqued axle nut.

● Check for poor gear alignmentas evidenced by uneven wear.

● Check for worn or looselanding gear components.

Vibration, shimmy and other similarconditions are usually blamed onimproper tire balance. Imbalance is a well known and easily understoodcause for vibration. In many casesthough, this may not be the cause.There are a number of specific aspectsof the tire, wheel and gear assemblywhich can be the cause or contributeto aircraft vibration. As with anyconcern, a systematic approach shouldbe taken to isolating its cause.

● Check that the tire has beeninflated to the properinflation pressure.• Follow the airframer’s

recommendation.• Be sure an accurate calibrated

pressure gauge has been used.

● Check that dual tire inflationis equalized between tires andper the operating specification.

● Assure that the tire reachedfull growth before it wasinstalled on the aircraft.• Allow at least 12 hours at

operating or rated pressure forthe tire to attain full growth.

● Check that the beads of the tirehave been properly seated.

● Check the tire for flatspotting or uneven wear.• If flat spotting does not extend

to the protector ply (Radial) or reinforcing ply (Bias) andvibration is acceptable, the tirecan be left in service.

● Verify that tires have beenproperly mounted.• For tubeless tires, the red

balance mark on the lowersidewall of the tire should bealigned with the wheel valve.

• For tube-type tires, the balancemark (light spot) on the lowersidewall of the tire should bealigned with the balance mark(heavy spot) on the tube.

● Check for air trappedbetween the tire and tube.• Use a soapy solution to check

for leakage at the base of thetube valve stem where it exitsthe wheel.

• Rolling the tire by taxiing will

Certain aircrafthave noselanding gearswhich aresensitive tovibration.For these cases,assembliesshould bechecked forbalance andwheel weightsadded whenrequired.

DDiissmmoouunnttiinngg

72 General dismounting instructions for aircraft tires

73

It is further recommended thatremoval information accompanythe tire to the repair station orretreader. The simplest approach isto use a tag or label attached to thetire with a self sticking adhesive(applied to lower sidewall) or by useof heavy or nylon string.

Caution: Do not use staples or other metal devices for affixingtags or labels to tires or inner tubes.Keep adhesive labels above the beadarea of the tire.

A sample label is shown above.

Removal from landing gear

Deflate any non-serviceable, damagedtire/wheel assembly before dismountingfrom the aircraft.Worn, serviceableunits may be left inflated.

Reason for removal - Tracking

In order to properly track reasons fortire removal and to take appropriateaction, it is very important to haveaccurate information regarding tireremoval. This information helps theretreader or repair station to makedecisions concerning inspections andthe future use of the tire.

Recommended informationincludes:

• Name of Operator • Date of dismounting • Aircraft model tail number • Tire part number • Tire serial number • Reason for removal • Number of tire landings

Tire dismounting

Proper dismounting proceduressimplify the job of servicing aircrafttires, while increasing safety andreducing the chances of damagingtires or wheels. The task ofdismounting tires should not beundertaken without properequipment, instructions and trainedpersonnel.

Careful attention must be given todisassembling and handling wheelcomponents to avoid damage tocritical surfaces. To assist in thisprocess, wheel manufacturerspublish specific instructions in theirmaintenance and overhaul manuals.Follow their recommendations andprocedures to assure trouble-freedismounting.

Tire/Wheel DismountingSequence

The same methods are essentially usedfor dismounting tubeless bias, tube-type bias and radial aircraft tires.However, radial tires have a smallerbead flat area and have a moreflexible sidewall, which requires thatmore attention be placed on thetooling set-up. Failure to use propertooling designed for the particular tiresize could result in dismountingdifficulties. Follow the toolingguidelines given in the next section.

Once tooling has been set-up,dismounting should occur in asimilar manner for both bias andradial tires, tubeless and tube-type.

● Before beginning any tiredismount, be sure to follow theinstructions and precautionspublished in the wheelsupplier’s maintenance manual.

● Mark damaged or bulge areasbefore deflating, using acontrasting color chalk.

● Completely deflate the tire or tube before dismounting.• Use caution when unscrewing

valve cores.The pressure within the tire ortube can cause a valve core tobe ejected at high speed.

• If damage has occurred, atire/wheel assembly should bedeflated in a protective cage.

● Use a bead breaker to loosentire beads from both wheel-halfflanges.• Always use proper bead breaking

equipment designed for separa-ting tires from wheel bead seats.Do not use pry bars, tire irons, or any other sharp tools to loosen tire beads. Damage to the tire and wheel may occur.

• Do not loosen wheel tie boltsprior to breaking the beadsloose. Damage to the matingsurfaces of the wheel halvescan occur.

• Ensure that the adaptor ringsof the ring type bead breakerhave passed over the wheelflanges and do not interferewith any wheel components.

• Ensure the faces of the adaptorrings or press pads, in contactwith the tire, are free of nicks,burrs or sharp edges whichcould damage the tire surfaces.

● Apply bead breaker rampressure or arm pressureslowly or in a series ofsequences or jogs to allow timefor the tire’s beads to slide onthe wheel. • Because of the flexible side-

walls of a radial, use of incor-rect tooling or applying pres-sure too rapidly can causesidewall distortion. Heavy dis-tortion of the sidewall is notonly harmful to the internaltire components, but it mayalso begin to “roll” the beads,making dismounting more dif-ficult.

General dismounting instructions for aircraft tires

74

RING

TIRE

WHEEL

Bead roll-over

procedure following the sameprocedure.

Note: Cases of bead roll over shouldbe reported to the retreaderwho will examine the tire fordamage. A tire found to havebeen damaged should bescrapped.

● Remove tie bolts and slide outboth parts of the wheel fromthe tire.

● For tube-type tires, remove thetube.

● Tire is now dismounted.

75

Tire Dismounting Equipment

The primary component fordismounting an aircraft tire from itswheel is the bead breaking equipmentused to loosen the tire from the wheelbead seats.

Two types of bead breakingequipment can be identified here:

● The “ring” type bead breaker.Bead breaking is performed bypushing a movable adapter ringagainst the lower sidewall ofone side of the tire. Theopposite side consists of astationary adapter ring that alsocontacts the lower sidewall ofthe tire.

It is important that the “adaptor”rings be designed for the particulartire/wheel assembly to be dismounted.

The optimum condition is anadapter ring internal diameter as close to the wheel flangediameter as possible. Pushingtoo high on the tire sidewall will

FIXED ADAPTOR RING

4" (100 mm) TRAVEL

0.4” (10 mm)RADIAL CLEARANCE

MOVABLE ADAPTOR RING

RAM

Ring-type bead breaker

● What To Do If The TireBecomes Fixed To The WheelIf a tire bead rolls such that it willno longer slide on the wheel:

• Release ram pressure.Apply a soap solution to the tire/wheel interface. Allow several minutes for thesolution to penetrate betweenthe tire and wheel.

Note: Do not use hydrocarbon-basedlubricants. These can be harm-ful to the rubber componentsof the tire.

• Reapply a reduced hydraulicpressure to the tire.

• Repeat several times if neces-sary.

If the tire still remains fast:

• Remove the tire/wheel assem-bly from the machine.

• Reinflate the tire in a cageuntil the bead moves back toits correct position.

• Deflate the tire.• Recommence the dismounting

only distort the sidewall andbead area, making dismountingmore difficult.

For practical purposes, a radialclearance between the tip of thewheel flange and the internaldiameter of the adaptor ring isnecessary to avoid interferencebetween the wheel and adaptorring as it approaches andtravels over the wheel flange.

Michelin recommends a radial clearance of 0.4 inches (10 mm).

The movement (travel) of theadaptor ring should be at leastfour (4) inches (100 mm) toensure complete separation ofthe tire from the wheel.

It is desirable that the rings bedesigned such that the tire canbe observed while pressure isbeing applied, to ensuresatisfactory ring contact andprogress.

● Localized “pincher” type beadbreaker.

This equipment consists of twopress arms which can beoperated in a “pincher”movement. At the end of eacharm is a press pad in the formof a sector. An adjustablecylinder is used to position thetire so that the sectors can bematched to the size of the tire.

The tire/wheel assembly ispositioned such that the presspads contact the tire’s lowersidewall just above the wheelflange.

Pressure is applied to break thebeads. After the first sector ofthe tire begins to move awayfrom the wheel flange, stop,rotate the tire/wheel assembly ashort distance and repeat theoperation until all sectors of thetire are loose and free from thewheel.

Note: When pressing against thetire, hold the pressure for 1-2 seconds to allow the beadtime to move. Bead breakingis most efficient when thetire/wheel assembly is rotatedapproximately 30 degrees bet-ween each pressing operation.

The press pads used to pushthe tire are “universal” and aredesigned to push on the tireclose to the wheel flange. Nospecific tooling is required forthe different tire sizes to behandled.

General dismounting instructions for aircraft tires

76

PRESS ARMS

PRESS PADS

Pincher-type bead breaker

RReettrreeaadd // RReeppaaiirr

77Retreading and repairingaircraft tires

Many aircraft tires that becomeinjured in service can be successfullyrepaired. Tires of which the treads areworn out, flat spotted, or otherwisedamaged, but of which the cord bodyis intact, can be retreaded. Retreadingand repairing aircraft tires has been acommon practice for many years andcan save aircraft operatorsconsiderable sums of money.Tires that might otherwise have beendiscarded due to insufficient ordamaged tread can be retreaded orrepaired for continued service, at acost much lower than that of a newtire. Retreading and repairing extendsthe service life of a carcass severaltimes past initial new tire usage.

FAA/JAA Regulations requireretreading and/or repairing of aircrafttires to be performed in certifiedretread and repair stations by orunder the responsibility ofqualified/certified technicians. Repairsby unauthorized sources are notrecommended.

Michelin meets or exceeds all testingrequirements of the FAA or JAA for retreaded aircraft tires.

Retreading Aircraft Tires

For aircraft tires, the term“retreading” refers to the methods ofrestoring a used retreadable tire byrenewing the tread alone or byrenewing the tread plus thereinforcing ply(s) or protector ply.

Full recapping is the recommendedprocedure for tires with evenly worntread, tires with flat-spotted tread, ortires with numerous cuts in the treadarea. The new tread material extendsaround and over the shoulder of thetire for several inches.

Accepting Tires for Retreading

Accepting tires for retreadingrequires careful inspection of allcomponents of the tire. Eachindividual tire is inspected by visualand air needle techniques prior to,during, and after the retreadingprocess. Shearography inspectioncan also be used to inspect forinternal defects which may limit theretreadability of a carcass.

Inspections must meet approvedprocess limitations for that tire to beretreaded.

Repairing Aircraft Tires

Many tires with injuries or damages canbe repaired at the time of retreadingand put back into useful/safe service.Injuries must be within themanufacturer’s repairable limits.

Tires with sidewall cuts, snags, scuffsand cracking from ozone can remainin service if the carcass ply is notexposed. Damages that exposecarcass textile can be repaired by anapproved repair station if the cordsare not cut or damaged.

Note: Repairable limits generallyexceed service-ability limitsused to remove tires from ser-vice. Detailed, safe inspectionssuitable for determining thegravity of an injury cannot bemade on inflated, mountedtires. Service removal limitsare further set to ensure safe operation and retreadability of the casing.

78

Retreading and repairingaircraft tires

Non-repairable aircraft tires

The following list outlines some ofthe conditions which can disqualifya tire from being retreaded:

● Any injuries to the beads or inthe bead area (except injurieslimited to the bead cover orfinishing strip).

● Weather checking or ozonecracking of tread orsidewall thatresults in exposed body cords.

● Protruding bead wire or kinkedbead.

● Ply separation.● Internal damage or broken cords.● Flat spots and skid burns that

have penetrated to the topcarcass ply. Wearing the tirebeyond the protector ply orreinforcing plies can leaveinsufficient interface rubber toallow retreading.

● Punctures that penetrate theinnerliner.

● Excessive brake heat damage,such as that experienced in anaircraft rejected takeoff.

● Tires that are heavily oil soaked.● Tires that have experienced a

major pressure loss.

● Sidewall RubberSurface defects on largecommercial tires may berepaired provided the repair isat least 1 inch from the beadheel, and no greater than anarea 11/2 inches (50 mm) by 4 inches (100 mm), and doesnot penetrate or damage thecarcass ply.

Repairable aircraft tires

The following are acceptable whenretreading aircraft tires:

● Tread AreaThe size of cuts and/or othertread injuries that can berepaired during retreading isdependent on many factors,including the injury’s length,depth and width as related tothe tire size itself. The numberand size of a repairable injury isalso dependent on theretreader’s repair methods andvalidation. If specific details onrepair limits are needed, seeyour Michelin retreader.

● Bead AreaMinor injuries to the bead areamay be repaired provided thecarcass plies are not damaged.

● InnerlinerInnerliner surface damage maybe repaired (bias tires). The size ofa repairable injury is dependenton the retreader’s repair methodsas well as government regulatorydocumentation.

79

OOppeerraattiinngg ttiippss

80 Operating and handling tipsfor better tire service

81

a scuffing action along the outeredges of the tread and results inmore rapid wear.

If an aircraft tire strikes a chuckhole,stone, or some foreign object lyingon the runway, taxi strip or ramp,there is more possibility of it beingcut, snagged or bruised because ofthe high operational deflection. If one of the main landing gearwheels, when making a turn, dropsoff the edge of the paved surface,this may result in severe sidewall orshoulder damage. The same type ofdamage may also occur when thetire rolls back up over the edge of thepavement.

With dual main landing gear wheels,it is important that they equallyshare the weight carried by thatlanding gear assembly.

As airports grow in size, and taxiruns become longer, chances for tiredamage and wear increase. Internaltire heat buildup also can be ofconcern. Speed, length of rolling andstops are all important in

influencing heat buildup. A taxispeed of 40 mph for 35,000 feet isdemonstrated during the TSOcertification of a tire. For either speeds or taxi distancesgreater than these limits, a 5-10 minutepause is recommended beforetakeoff.

For less foreign object damage intaxiing, all personnel should makesure that ramps, parking areas, taxistrips, runways and other pavedsurfaces are regularly cleaned andcleared of all objects that mightcause tire damage.

Pivoting By Using Brakes

Increased airport traffic and longertaxi runs are subjecting tires to moreabrasion from turning and pivotingwhile braking.

Severe use of brakes under pivotingconditions can wear flat spots ontires and cause them to become outof balance, making prematureretreading or replacement necessary.Pivoting on surfaces with heavytexture or a step condition can

Optimized tire performance is directlyrelated to the use and care the tire isgiven.While the single most importantaction for obtaining optimum tireperformance is a program of regulartire inflation maintenance, user (pilot)actions and the condition of theairport surfaces are also important.The following information is to helpbring an awareness of these importantfactors which can further your tireinvestment.

Taxiing

Unnecessary tire damage andexcessive wear can be prevented byproper handling of the aircraftduring taxiing.

Most of the gross weight of anyaircraft is borne by the main landinggear which may consist of two, four,eight, or more tires. The tires aredesigned and inflated to absorb theshock of landing and will normallydeflect about three times more thana passenger car or truck tire. Thegreater deflection allows the tire tocarry the heavy loads. It also causesmore working of the tread, produces

locally tear the tread from thecasing. This tear may not show as aseparation until later in the tire’sservice life.

Careful pivoting of an aircraft alsohelps prolong tire tread life. When anaircraft is turned by locking onewheel (or wheels), the tire isscrubbed, with great force, againstthe pavement. A small rock or debristhat would ordinarily cause nodamage can virtually be screwedinto the tire. This scuffing andgrinding action takes off treadrubber and places a very severestrain on the sidewalls and beadareas of the tire at the same time.Making wide radius turns will reducetread rubber removal and sidewallstresses.

Condition of Airport Field

Regardless of preventive maintenanceand the care taken by pilot andground crew, tire damage is almostcertain to result if runways, taxi strips,ramps and other paved field areas arein bad condition, strewn with debrisor poorly maintained.

Chuckholes, pavement cracks or step-offs in the pavement can all cause tiredamage. In cold climates, especiallyduring winter, all pavement breaksshould be repaired immediately.

Accumulated debris on paved areas,including hangar floors, is especially hazardous. Stones and other foreignmaterial should be kept swept off allpaved areas. Special attention shouldbe paid to make sure that tools, bolts,screws, rivets and other repairmaterials are not left lying on anaircraft so that when it is moved, theyfall to the floor. If a tire rolls over suchmaterial it can result in punctures, cutsor complete failure of the tire and tube.

Avoid Chemical Contamination

Chemicals and hydrocarbons suchas jet fuel, hydraulic fluids, grease,cleaning agents, etc., can damageaircraft tires by softening ordeteriorating the rubber surface.During aircraft maintenance, tiresshould be covered to protect themfrom accidental spills. Keep runwaysurfaces clean so that tires are not parked in surface puddles.

Immediately upon contact with ahydrocarbon substance, wash thecontaminated area first withdenatured alcohol then with a soapand water solution. If the rubberfeels soft or spongy when probed,remove the tire from service.

Nylon Flat Spotting

Nylon aircraft tires will develop flatspots under static load. The degree ofthis flat-spotting will vary according to:

● the temperature of the tirewhen the aircraft is first parked,

● the pressure in the tire,● the load being applied to the

tire while the aircraft is parked,● the ambient temperature,● the length of time the tire is

subject to a combination of theabove conditions,

● the type of construction (undersimilar conditions, a radial tirewill develop less flat spottingthan will a bias tire).

On a practical level, aircraftmaintenance personnel cannotinfluence all of these variables.

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Operating and handling tipsfor better tire service

To minimize the condition, inflationpressures should be kept at theirspecified operating levels and loadsheld to a minimum during the staticload period.

Under normal conditions, a flat spotwill disappear by the end of the taxirun. In the unusual case where deepflat-spotting has occurred, additionaltaxiing is recommended prior to take-off.

An aircraft that is to remain idle for aperiod longer than three days shouldeither be moved every 72 hours orblocked up so that no weight is on thetires. Aircraft in storage (out of servicefor more than 14 days) should beblocked up so that there is no weighton the tires.

Chevron Cutting

Cross-cutting of runways is commonat many major airports around theworld. It improves drainage, reducesthe danger of standing water andthus, decreases the risk ofhydroplaning. However, the sharp-edged ridges of concrete that result

occurs. This action is usually referredto as “dynamic hydroplaning.” Itsoccurrence is a function of waterdepth and aircraft speeds.

The same phenomenon can resultwhen a thin film of water on therunway mixes with the contaminantspresent or if the surface texture of therunway is smooth. This is called“viscous hydroplaning.” Generally the irregular condition of the runwaysurface is sufficient to break up this film.

Today, most airport runways aredesigned to minimize water buildup.Cross-grooving is one example. Inaddition, tires have circumferentialgrooves which help to dissipate water.

An aircraft tire experiencinghydroplaning (usually viscoushydroplaning) may form an area ofreverted rubber or skid burn in thetread. This area will be oval in shapesimilar to a flat spot. If the reinforcingply or protector ply is not exposed,the tire can remain in service.

can cause chevron-type cutting of thetire tread ribs, particularly on the highpressure tires used on jet aircraft.

Chevron cutting occurs during aircrafttouchdown at “spin-up”. As the tirebegins to accept aircraft loads, it deforms slightly in these cross-grooves. At the same time rapidacceleration is occurring. The forcesrequired to accelerate the tire toground speed cause a tearing actionwhich forms the chevron.

These cuts are at right angles to theribs and rarely penetrate to the fabrictread reinforcement ply or protectorply. Refer to the section on “TireServiceability Criteria” for handlingthis condition.

Hydroplaning

This condition results when, on a wetrunway, the tire’s tread is progressivelylifted off the runway surface. A waveof water builds up in front of a rollingtire, allowing the tire to ride on thewater and lose contact with therunway surface. Loss of traction,steering ability and braking action

83

84

Operating and handling tipsfor better tire service

Note: A similar reverted rubbertread condition can occur if the tire slides on ice for any distance.

Tire removal criteria should be basedon operational and tire conditionfactors. Factors to be considered are:runway cross-grooving, tire footprint area (number and remaining depth ofgrooves), and level of runway flooding.When operational and tire conditionfactors are conducive to hydroplaning,removal criteria should be adjustedaccordingly.Contact Michelin for detailedinformation.

Landings per tread

Tire performance can be improvedby using slow taxi speeds and by letting the aircraft roll duringlanding and by avoiding hardbraking.Whenever possible, make largeradius turns which minimize tirescrubbing.

Design:

• Michelin Aircraft Product Line

• Studio graphique Michelin

• Gris souris

Photos:

- Air Bourget

- Boeing

- Gajic

- Mc Donnell Douglas

- Michelin

- Sirpa Air: Gauthier

- Trebosc

Printing:

• Imprimerie Fabrègue

Research &DevelopmentCharlotte - U.S.A.

Greenville - U.S.A.

Ladoux - France

ManufacturingPlantsBourges - France

Nong Khae - Thailand

Norwood - U.S.A.

Retread ServiceCentersBourges - France

Cuneo - Italy

Kansas City - U.S.A.

Nong Khae - Thailand

Norwood - U.S.A.

HeadquartersMichelin Aircraft Tyre

23, place des Carmes-Déchaux

63040 Clermont-Ferrand Cedex 9 - France

Tel: 33 (0)4 73 32 76 40 - Fax: 33 (0)4 73 32 76 42

Commercial OfficesNorth, Central and South America :

Michelin Aircraft Tire Corporation

1305 Perimeter Road

Greenville, SC 29605 - United States

Tel: 1 864 422 7000 - Fax: 1 864 422 7071

Europe, Middle East and Africa:

Michelin Aircraft Tyre

23, place des Carmes-Déchaux

63040 Clermont-Ferrand Cedex 9 - France

Tel: 33 (0)4 73 32 76 36 - Fax: 33 (0)4 73 32 76 44

Far East and Oceania:

Michelin Aircraft Tyre Asia

SPE Tower 12th Floor

252 Phaholyothin Road

Samsaen Nai, Payathai

Bangkok 10400 - Thailand

Tel: (66 2) 619-3530 - Fax: (66 2) 619-3069

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