GROUND OPERATION AND SERVICING

Fire Protection 607 Nature of Fire 608 Classification of Fires Fire Extinguishing Agents

608

Fire Extinguishers 609 608

Water Fire Extinguishers 609 Halon/211 and 1301 Fire Extinguishers 610 Carbon Dioxide Fire Extinguishers 611 D ry-Powder Fire Extinguishers 611

Study Questions: Fire Protection 612

Safety in the Shop and on the Flight Line 613 Safety Involving Compressed Gases 613 Hearing Protection 614 Eye Protection 614 Respiratory Protection 614 Shop and Flight Line Safety Summary 616

Aviation Fuels 616 Reciprocating-Engine Fuels 616 Jet Fuels 619 Study Questions: Aviation Fuels 620

Aircraft Fueling 622 Preparation for Fueling 622 Over-Wing Fueling 623 Pressure Fueling 625 Defueling 626 Study Questions: Aircraft Fueling 626

0ROU:\D OPERATION AND SERYICI:\G

10

Continued

Chapter 10 605

Aircraft Movement 627 627 Towing Aircraft

Taxiing 628 Helicopter Movement 631 Study Questions: Aircraft Movement 631

Aircraft Tiedown 632 Normal Tiedown 632 Preparation for Severe Weather 634 Securing Helicopters 634 Study Questions: Aircraft Tiedown 635

Aircraft Jacking and Hoisting 636 Aircraft Jacking 636 Aircraft Hoisting 637 Study Questions: Jacking and Hoisting 637

Aircraft Icing Protection 638 Study Questions: Icing Protection 639

Engine Operation 639 Reciprocating Engines 639

Starting Engines Equipped with Float Carburetors 640 Starting Engines Equipped with a Fuel Injection System 641 Hand Cranking a Reciprocating Engine 642

Turbine Engines 642 Turbine Engine Starting 642

Improper Starts 644 No Oil Pressure 644 Hot Start 644 II ung Start 644

Study Questions: Engine Operation 645

Answers to Chapter 1 0 Study Questions 64 7

606 A VIATION M A INTENANCE T ECHNICIAN -

G ENERAL

GROUND OPERATION AND SERVICING

One of the important functions of an aviation maintenance technician is that of operating aircraft on the ground. This involves servicing it with the proper fuel and lubricants. In this section of the text, we will discuss safety proce-dures in the shop and on the flight line. We will also discuss the various fuels and the precautions to be observed when fueling an aircraft. Finally, since moving aircraft and running their engines are important parts of an aviation maintenance technician's work, we will discuss the basic procedures for start-ing both reciprocating and turbine engines, and the precautions to be observed when moving aircraft on the ramp and in the hangar.

Fire Protection Aircraft carry huge quantities of fuel, and because of the large amount of electrical wiring and equipment. fire is always a potential danger. It must be guarded against at all times by the maintenance technician. This not only means taking safety precautions on the actual aircraft, but also in the hangar area and the maintenance shops.

All combustibles must be kept in the proper type of containers and stored in areas specially approved for them. Many combustible materials such as lacquer, dope, and paint thinners must be stored in an area where there is adequate ventilation.

Spilled gasoline presents a special fire hazard, and it must not be swept with a dry broom, as static electricity can be generated that will cause a spark and ignite the fumes. A small amount of gasoline can be picked up by cover-ing it with an industrial absorbent and carefully disposing of the material in a manner approved by the local fire department. Large amounts of gasoline spilled around an aircraft should be flashed away from the aircraft with wa-ter and the local fire department notified.

Paint spray booths that have been used for spraying lacquer and dope often have dried overspray on the floor. Do not dry-sweep such a spray booth, as the friction can produce static electricity and ignite the flammable dried overspray. Always wet the floor before sweeping it.

Rags that are wet with oil, paint solvents, thinners, and certain chemi-cals such as Alodine and other conversion coatings must not be kept in a pile. These materials combine with oxygen in the air and generate heat, which if not allowed to escape will raise the temperature inside the pile high enough

GROUND 0 PERATfO'\ AND S ERVfC!NG

10

flammable. Easily ignited. Flammable replaces the older term "inflammable'' which can be misinterpreted to mean ' not flammable."

Chapter 10 607

HEAT Figure 10-1. Three things are required for a fire: fuel, oxygen, and heat. If any one of the three is missing there can be 110 fire.

spontaneous combustion. Ignition of a material without an external source of heat. The heat that causes the ignition is provided by oxidation, and if it is not allowed to escape, the temperature will rise to the combustion temperature of the material.

Piles of oily rags, or rags containing certain chemicals are subject to spontane-ous combustion.

kindling point. The temperature to which a material must be heated for it to combine with oxygen from the air and burn.

halogenated hydrocarbon. A chemical compound containing hydrogen and carbon and one of the halogen-family elements such as fluorine, chlorine, or bromine.

The vapors of halogenated hydrocarbons are particularly effective as fire extinguish-ing agents as they chemically prevent the combination of the oxygen with the fuel.

608

to cause them to ignite spontaneously and burn. The chemicals should be washed out and the rags allowed to dry in a ventilated area. Oily rags should be stored in airtight safety containers.

Nature of Fire Fire is the product of a chemical reaction in which a material, called a fuel, combines wi th oxygen and releases heat and light. The fuel is usually changed into carbon wh ich unites with some of the oxygen to form carbon dioxide and carbon monoxide.

Three things are required for a fire: There must be fuel, there must be oxygen, and the temperature of the fuel must be raised enough for it to com-bine with the oxygen. Fire prevention consists of keeping these three con-stituents separated. Fire extinguishing is done by cooling the fuel or excluding oxygen from it.

Classification of Fires Fires are classified into four categories that allow us to better understand them and choose the correct method for exti nguishing them. Extinguishers suited for each classification of fire are marked with the classification letter desig-nation and distinctive mark recommended by the National Fire Protection Association. See Figure I 0-2.

Fire Letter Classes Designation Symbol Ordinary combustibles A Green triangle Flammable liquids 8 Red square Energized

electrical equipment c Blue circle Combustible metals D Yellow star

Figure 10-2. Classification of fires

Fire Extinguishing Agents Fire extinguishing agents are chosen for the class of fire on which they are ef-fective, and they should be clearly marked with the appropriate class symbol.

Class A fires, with such fuels as paper, cloth, or wood, can be extinguished with a spray of water which cools the fuel to a temperature below its kin-dling point.

Class B fires are best put out with an extinguisher that excludes the oxy-gen from the burn ing fuel. Carbon dioxide, or C02> extinguishers blanket the fire and exclude the oxygen. Dry powder extinguishing agents, in the pres-ence of heat break down to produce carbon dioxide that displaces the oxy-gen. Halogenated hydrocarbons such as Halon 121 1 and Halon 1301 are highly effective for these fires, as they form a chemical reaction that prevents

A VIATION M AINTENANCE T ECII1\'ICIAN G ENERAL -

the oxygen and the fuel uniting. Water should not be used on a Class B fire because many of the burning fuels~ ill float on the water and spread the fire.

Class C fires should be handled with special care because of the danger of contacting dangerously high voltages. Water should not be used because it will conduct the electricity. Dry powder. while effective on Class C fires. is not the best choice because the residue it leaves makes cleanup difficult. Carbon dioxide, when sprayed through a nonmetallic horn is very effective. but the best extinguishers are the halogenated hydrocarbons, the halons.

Class D fires should never have water sprayed on them as the water only intensifies the fire, and it can. in extreme cases, cause an explosion . Dry powder, which excludes oxygen from the flame, is the choice for extinguish-ing metal fi res.

Toxicity Group 6 (least toxic) Sa 5 4

3 2

Extinguishing Agent Halon 1301 (Bromotrifluoromethane) Carbon dioxide Halon 1211 (Bromochlorodifluoromethane) Halon 1202 (Dibromodifluoromethane) Halon 1011 (Bromochloromethane) Halon 1001 (Methyl bromide)

Figure I 0-3. Fire extinguishing agents arranged according 10 /heir wxicity. The higher 1he number, the less wxic 1he age111.

Fire Extinguishers All fire extinguishers are not equally effective on all types of fires. The size of the extinguisher and the extinguishing agent it contains must be chosen for the classes of fires that are most likely to occur at the location the extinguisher is mounted. The class of fire for which the extinguisher is suited is marked near or on the extinguisher with the symbols described in Figure I 0-2.

Water Fire Extinguishers Small metal containers of water and an antifreeze agent may be mounted in brackets in the aircraft cabins to extinguish class A fires. The seal in a small C02 cartridge in the handle of these extinguishers is pierced when the handle

GROU\0 OPERATIO:'< A\D SER\"ICI\G Chapter 10 609

610

is twisted. The released C02 pressurizes the water and sprays it out so it can effectively lower the temperature of the fuel and extinguish the fire. See Figure 10-4.

~ 61?-~-- C02 cartridge

~+----------- Water cartridge

Figure 10-4. When the handle ofthisfire extinguisher is twisted, the seal on the C02 cartridge is broken and the water in the cylinder is pressurized and sprays OIIIIO extinguish the fire.

Halon 1211 and 1301 Fire Extinguishers Halon 121 I and 1301 are two of the most effective fire extingu ishing agents available for use on class B and C fires and are also effective on Class A fires. They are colo rless, noncorrosive liquids that evaporate rapidly and leave no residue, and they do not harm fabrics, metals, or other materials they con-tact. Halon 121 1 and 130 I extinguish fires by producing a heavy blanketing mist that eliminates air from the fire, and their chemical action inhibits oxy-gen combining with the fuel.

AVIATION M AINTio ANCE T ECIINICIA\' GENERAL -

Halon 1211 and 1301 extinguishers meet the requirements of 14 CFR 135. 155 for installation in aircraft engaged in air taxi operation and are available in small , medium, and large sizes. The small size is capable of ex-tinguishing fires of up to one square foot in area, the med ium extinguisher is effective on fires of up to two square feet. and the large exting uisher is effec-tive on fires up to fi ve square feet. Halon 1211 uses nitrogen to propel the agent from the extinguisher but Halon 130 I does not require a separate pro-pelling agent. All of these extingui hers are equipped with gages to indicate the pre sure of the extinguishing charge.

Carbon Dioxide Fire Extinguishers C02 is an inert gas that is stored in a steel container under pressure. When it is re leased it expands and its temperature drops. It blankets the fire and ex-cludes oxygen so the fire goes out. C02 extinguishers are avai lable in sizes ranging from smal1 2-pound units for installation in aircraft cabins and cock-pits to the large wheel-mounted extinguishers fo r use in maintenance shop and on flight lines.

The state of charge of a C02 fire extinguisher is determined by weighing it and comparing its weight with the weight stamped on the extinguisher housing. If the weight is less than that stamped on the housi ng. the extin-guisher must be re turned to a service fac ility for recharging.

Dry-Powder Fire Extinguishers Dry powder fire extinguishing agents such as bicarbonate of soda. ammo-nium phosphate and potassium bicarbonate are effective against class B. C. and D fires. When the agent is heated. it releases carbon dioxide and excludes oxygen from the fire. Dry powder fire extinguishers a re not applicable for cockpit fires because o f the reduced visibi lity they cause. They are, however. most effective for brake fires which involve burning metal.

The dry powder extinguishing agent is propelled from the container by a charge of compressed dry nitrogen, and the condition of the charge is indi-cated by a pressure gage built into the exting ui sher.

G ROUND O PERATIO"\ A"\D S ER\ICI"\G Chapter 10 6 11

STUDY QUESTIONS: FIRE PROTECTION Answers are on Page 647. Page numbers refer to chapter text.

I. Three things that are necessary for a fire are: a. ____________________________________ _

b. __________________________________ __ c. ____________________________________ _

Page 608

2. A fire involving paper as a fuel is a class- fire. Page 608

3. A fire involving a flammable liquid as a fuel is a class- fire. Page 608

4. A fire involving an energized electrical system is a class- fire. Page 608

S. A fire involving combustible metals is a class- fire. Page 608

6. A fire extinguisher suitable for use on a Class-A fire is identified by a ----------------. Page 608

7. A fire extinguisher suitable for use on a CJass-B fire is identified by a _____ ___ _ ______ .Page608

8. A fire extinguisher suitable for use on a Class-C fire is identified by a _ _ ___ _________________ .Page608

9. A fire extinguisher suitable for use on a Class-D fire is identified by a ________________ .Page608

10. A fire extinguishing agent with a toxicity rating of 2 is ___________ (more or less) toxic than one with a rating of 6. Page 609

612 AVIATION MAINTENANCE T ECHNICIA:-. GENERAL -

Safety in the Shop and on the Flight Line Shop and flight line safety are extremely important parts of a technician's responsibility, and we must make safety awareness a way of life. Mainte-nance shops contain both visible and invisible hazards which must be recog-nized and guarded against.

Good housekeeping dictates that we immediately wipe up any liquids spilled on the floor and that we properly dispose of dirty and oily rags. Waste containers should be emptied frequently to prevent the accumulation of un-neces ary flammable materials in the shop.

All power tools such as saws. sanders. grinders, and power hears should be kept clean and free of obstructions that make their operation awkward. And no one should be allowed to operate any power tool until he or she is properly checked out and aware of all of its safety features and requirements.

We should even be aware of such seemingly insignificant things as the proper disposi tion of used safety wire. These harp pieces of wire can cut a person. and if they fall into an electrical junction box can cause an electrical malfunction or, even worse. a fire. If they fall into an engine or other me-chanical device, they can cause expensive damage.

The time pressure under which we often work can cause us to be care-less with our tools. Tt is an exceptionally good idea, when working on an air-craft to know exactly which tools we have with us and, when the job is complete, to account for each tool. Some operators even require a written tool list for on-the-aircraft work to minimize the chance of a tool being left in an aircraft structure or in an engine. Tools left in an aircraft control sys-tem or engine can cause serious accidents.

The welding area in a shop should receive special attention because of the flammable gases stored under pressure and the presence of sparks and flying particles of molten metal. When welding or cutting is done outside of the designated welding area. special care must be taken to prevent the flame or sparks igniting any flammable materials. Adequate fire extinguishers must always be available when welding or cutting is being done.

Safety Involving Compressed Gases Most aviation mai ntenance shops use various gases under pres ure that must be properly hand led to insure safety. Some basic rules to observe when han-dling compressed gases are: 1. U e special caution when moving a bottle of compressed gas. Always

have a cap installed over the valve. and trap the bottle to the cart to prevent it rolling off.

Continued

GROUND 0PERATIO\; .\\;() SER\ ICI:\G Chapter 10 613

614

2. Always use some sort of eye protection when working with compressed gases, and do not direct any compressed gases toward a person. When using compressed air to blow dust and dirt away, be sure that the pressure is low enough that the flying particles cannot injure anyone.

3. Do not use oil or grease on an oxygen cylinder or regulator, as the pure oxygen can cause the petroleum product to spontaneously ignite.

Hearing Protection The high noise level of rivet guns, air drills, metal saws, and operating tur-bojet engines requires that everyone in aircraft maintenance shops and on the flight lines use some form of hearing protection.

When a person is exposed to the noise for a relatively short period of time or in locations where the noise level is relatively low, small protectors that fit into the auditory canal ofthe ear are quite effective. One very popular type of protector consists of small plugs of sponge plastic that are formed into cones and inserted into the ear. When inside the ear, they expand to form a perfect fit in the auditory canal and decrease the sound pressure reaching the ear drum.

When working on a noisy flight line, most technicians use a hearing pro-tector that resembles a large set of cushioned earphones and is held over the ears with a spring steel band. This is comfortable and provides a large de-gree of protection. See Figure 10-5.

Eye Protection Our eyes are two of our most valuable assets and we should protect them against all types of hazards. One common type of eye protection for persons who wear prescription eye glasses is the use of special safety lenses with trans-parent plastic side shields. Another type of eye protector is safety glasses made of a soft but strong transparent plastic material that cover the eyes and are held on the head with an elastic band. The sides of these glasses fit snugly against the face to prevent injury from the side, and the sides are ventilated to keep the lenses from fogging.

Full-cover face shields that are mounted on an adjustable head band and wrap around the face should be used when working on air conditioning sys-tems and when charging liquid oxygen systems to prevent injury from the extreme cold if any liquid refrigerant or oxygen is splashed on the face.

Respiratory Protection There are two types of airborne contaminants that can be injurious to our lungs: solid particles and vapors; and we must protect our lungs from both of them.

Disposable paper or cloth masks are often used to protect against solid contaminants and shou ld be used when sanding or grinding composite materials.

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Spraying paints, lacquers, and enamels produce solid contaminants in the air as well as harmful vapors. You should use a mask that has a pre-filter to remove the solid contaminants and then a chemical cartridge to provide pro-tection against the vapors. When it is necessary to work in an environment containing a heavy concentration of toxic vapors, an airflow-type respirator should be worn. This respirator covers the entire head and upper part of the body and is supplied with a constant flow of compressed air that prevent fumes entering the mask.

Figure 10-5. Ear protectors for use on a noisy flight line.

GROUND OPERATION A:-.iD SERVICING Chapter 10 615

vapor pressure. The pressure of the vapor above a liquid required to prevent the liquid releasing additional vapors.

vapor lock. A condition in a fue l system in which the fuel has vaporized and formed pockets of gas in the fuel line . Vapor lock prevents liquid fuel flowing to the engine .

detona tion. An explosion-like uncon-trolled burning of the fuel-air mixture inside the cylinder of a reciprocating engine when the fuel-air mixture reaches its critical pressure and temperature. Detonation causes a rapid rise in cylinder pressure, excessive cylinder head tempera-ture, and a decrease in engine power.

616

Shop and Flight Line Safety Summary Operating jet engines act as huge vacuum cleaners and pick up loose objects on the ground, and many have been seriously damaged by sucking up bolts, pieces of sheet metal, safety wire, and tools. Many flight lines and aircraft parking ramps have containers for any debris you may find on the ground and for any li tter you may need to dispose of. Make it a habit to pick up any li tter and properly dispose of it.

A good technician not only cleans up after completing a task, but is al-ways alert to any potentially dangerous situation that may have been left by someone else. Safety is really as much an attitude as it is an action.

Aviation Fuels Reciprocating-Engine Fuels Aviation gasoline is a blend of hydrocarbons obtained from crude petroleum by the process of fractional distillation. It has a nominal heat energy content of 20,000 Btu per pound, and it weighs approximately six pounds per U.S. gallon.

Aviation gasoline does not burn in its liquid state, but it readily changes from a liquid into a vapor, and these vapors combine with oxygen from the air to form a combustible mixture. The vapor pressure of a fuel is the pres-sure that must be maintained above the liquid to prevent it releasing vapors. The vapor pressure of aviation gasoline is carefully controlled to assure that it vaporizes easily enough for the engine to start in cold weather, but not so easily that it wi ll cause a vapor lock in the fuel lines.

Aviation gasoline is required to have a vapor pressure of 7 psi or less, at I 00F.lf it vaporizes too readi ly, its vapor pressure will be high and when a bubble forms in a fuel line, the pressure of the vapors in the bubble will pre-vent fuel fl owing to the engine and the engine will not run. This condition is called a vapor lock, and it forms when the fuel gets too hot or when the air-craft goes high enough that the air pressure above the fue l drops enough to allow the fuel to release vapors, or boil.

One of -the I imits to the development of high-powered reciprocating engines has been the detonation characteristics of the available fuel. Detonation is an uncontrolled burning, or explosion, of the fuel-ai r mixture inside the cylin-der of a reciprocating engine. The mixture ign ites and burns normally, but as it burns, it compresses and heats the mixture ahead of the flame front. When the heated and compressed mixture reaches its critical pressure and tempera-ture, it explodes, or releases its energy almost instantaneously. These explo-sions inside the cyl inder increase the cylinder-head temperature and cylinder pressure and decrease the engine power. Severe detonation can destroy an aircraft engine.

The antidetonation characteristics of aviation gasoline are indicated by an octane number or performance number, and the FAA specifies in the Type

AVIATIO:-: MAINTENANCE TECHNICIAN GENI RAL

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Certificate Data Sheets (TCDS) for each engine the m inimum grade of fuel approved for that engine. If fuel of a lower grade than is approved for the engine is used, there is a serious danger of detonation, and it is a violation of the Federal Aviation Regulations to service an aircraft with fuel having an octane rating lower than the minimum specified in the TCDS.

Aviation gaso line is dyed to identify its octane rat ing or performance number. and these colors and their meanings are listed in Figure 10-6.

Grade 80 82 UL 100 100LL Jet fuel

Color Red Purple Green Blue Colorless

Max. TEL (MIIgal) 0.5 Unleaded 4.0 2.0

Figur e 10-6. /demification of grades of miation gasoline

Notes

Being phased out

The octane rating or performance number of a gasoline is determined by burning the fuel in a special variable-compression ratio laborato ry test en-gine. called a CFR (Cooperative Fuel Research) engine, and comparing its perfo rmance with that of a reference fuel made up of iso-octane and normal heptane. Iso-octane is a flammable. colorless hydrocarbon liquid that has a high clitical pressure and temperature. It is used as the high reference and has bee n assigned a rating of 100. ormal heptane is another hydrocarbon liquid. but it has poor antideronation characteri tics and is u ed as the low reference and assigned a rating of zero.

The test engine is operated with a standard reference fuel (usually iso-octane) with operating conditions adjusted to standard day condi tions. Thi produces a standard knock, and a knockmeter that measures peak combustion pressure is adjusted to a midscale setting of 50 to 55. The sample fuel with an unknown octane rati ng is now introduced into the induction system and the fuel-air ratio is adjusted to produce maximum knock. The compression ratio is then adjusted to return the knockm.eter to the same reading as previously noted. The new compression ratio is checked in a reference table to determine the approximate octane rating of the fuel. This rating is verif ied by using a fuel composed of a mixture of iso-octane and normal heptane, with the percentage of i o-octane the same as the rating found in the CFR engine. This fuel should have the same knock characteristic as the sample fuel produced.

Gasoline with an octane ra ting of 100 has the same antidetonarion char-acteristics as iso-octane, but some gasoline has better characteristics, and it is rated with performance numbers determined by using a reference fuel compri sed of iso-octane containing controlled amounts of tetraethyl lead.

You will sometimes see a dual-number rating for aviation gasoline. T his system gives the antidetonation rating for the fuel when it is operating with

G ROUND O PERATION ASD S ERVICI'\G

T ype Certificate Data Sheets (TCDS). The official !>pecifications of an aircraft. engine. or propeller issued b} the Federal Aviation Administration.

TC DS for an engine lists the minimum grade of fuel approved for its u~e.

fuel grade. A system of rating m iation gasoline according to its antidetonation characteristics. This is ba-,ed on the older system of octane rating or performance number in which the higher the number. the more resistant the fuel i' to detonation.

performance numbers. An antidetonation rating system for aviation gasoline whose performance characteristic' are better than those of iso-octane. which i~ used as the top value in the octane rating '>ystem. Aviation gasoline rating~ above I 00 are called perfo rmance number~.

iso-octanc. T he hydrocarbon fuelu~ed as the high reference when raring the antidetonation characteristics of a\ iation gasoline.

sta ndard day conditions. Conditions chosen by ~cientisr~ and engineer~ that allo"" all rest data to be corrected to the same condi tions. These conditions include: Temperoture: 15C or 59 F Sea lele/ prenure: 29.92 inches of

mercury. or 1013.2 millibar-. Acceleration due to grariry: 32.2 feet per

second, per second Specific weigh1 ofair: 0.07651 pounds

per cubic foot Density: 0.002378 slug per cubic foot Speed ofsound: 661.7 knot\. or 761.6

miles per hour

Chapter 10 617

tetraethyl lead (TEL). A poisonous compound added to aviation gasoline to increase its critical pressure and tempera-ture. TEL inhibits detonation and improves the performance of the fuel in the engine. Fuels contain ing TEL are being phased out.

ethylene dibromide. A compound added to leaded aviation gasoline that converts some of the lead oxides into more volatile lead bromides so that they will pass out of the cylinder with the exhaust gases. This reduces lead fouling of the spark plugs.

volatility. The characteristic of a liquid that relates to its ability to vaporize, or change into a gas.

trichresyl phosphate (TCP). An additive to aviation gasoline that he lps scavenge lead deposits from the cyl inders by converting lead bromides to the more volatile lead phosphates.

manifold pressure. The absolute pressure inside the induction system of a reciprocat-ing engine.

6 18

both a lean and a rich mixture. A fuel rated as 100/1 30 has an octane rating of 100 when the engine is operating with a lean, or cruise, mixture, and a performance number of 130 when it is operating with a rich mixture, such as would be used for takeoff.

Tetraethyl lead (TEL), a heavy, oily, poisonous liquid [Pb(C2H5)4] is added to aviation gasoline to improve its antidetonation characteristics by raising its critical pressure and temperature. This allows the engine to oper-ate with higher cylinder pressures without the fuel-air mixture detonating. But TEL has the problem of leaving lead deposits inside the cylinders that foul spark plugs and cause corrosion. The maximum amount of TEL allowed in the various grades of aviation gasoline is seen in Figure 10-6.

In order to get rid of the lead residue from the TEL, ethylene dibromide is mixed with the gasoline. When the gasoline bums, the ethylene dibrornide combines with the lead to form volatile lead bromides that go out with the exhaust gases instead of forming solid contaminants ins ide the cylinder.

The decline in the number of low horsepower engines in the general aviation fleet has caused such a decrease in the demand for grade 80 gaso-line that it is often unavailable. When an engine designed to operate on grade 80 fuel must operate on grade 100 or I OOLL there is too much lead, and spark plug fouling is likely to occur even with the ethylene dibromide. Another compound, trichresyl phosphate [(CH3C6H40)3PO], commonly called TCP, may be added to the fuel. TCP changes the lead deposi ts into a nonconduc-tive lead phosphate which is easier to eliminate from the cylinder than the lead bromide.

The critical pressure and temperature of a fuel may be increased by blend-ing aromatic addi tives such as benzoil, toluene, xylene, and cumene with the fuel. These additives, first commonly used during World War II, allow the engine to use a higher manifold pressure and thus produce a higher horse-power without the danger of detonation. They do have the drawback that they soften certain rubber products. Because of this softening action, most of the hoses and diaphragms used in aircraft fuel systems are made of rubber com-pounds that are not affected by aromatic additives.

We have mentioned that the use of a fuel with an octane rating or perfor-mance number lower than that approved by the FAA can lead to detonation and engine damage or destruction. A condition more dangerous than using aviation gasoline with too low an octane rating results if the gasoline is con-taminated with jet fuel. Jet fuel is not designed to burn under the pressures encou ntered in a reciprocating engine, and it takes only a small amount of jet fuel to lower the critical pressure and temperature of the fuel to such a level that catastrophic detonation can occur. If any tanks on a reciprocating-engine aircraft have been serviced with jet fuel, they should be drained, and all of the lines, valves, and strainers flushed. If the engine has been operated

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on the contaminated fuel, the cylinders should be inspected with a bore-scope to c heck for internal damage. and the engine should be given a com-pre sion check. The oil should be changed and the oil filters inspected for any indication of contaminants that could re ult from detonation.

The decrea e in availability and increase in price of g rade 80 aviation gasoline ha caused many aircraft owners and operators to consider the use of automo-tive gasoline. Some aircraft have been operated safe ly with automobile gasoline without the approval of the FAA, but within the last few years the FAA has issued supplemental type certificates (STCs) that allow the use of automobile gasoline in certain aircraft under pecific conditions. Aircraft and engine manufacturers and the major oil companies have advised against the u e of automobile gasoline in aircraft engine because its production, storage, and handling requirements are not as rigid as those imposed on aviation gasoline. Automobile gasoline often has vapor pressures as high a 15 psi at I 00F, and this can cause vapor lock at high altitudes. T he additives in auto-mobile gasoline may be incompatible with the seals and diaphragms in air-craft fuel ystems. A lso, the lack of stringent government controls may allow the characteristics of automobile gasoline to vary from one batch to another.

As the cost of aviation gasoline continue to rise and as more experience is gained using automotive gasoline, its use and acceptance will urely in-crease. Under the present conditions. be sure, when servicing an aircraft with automotive fuel, that the aircraft and engine are covered by a valid STC and al l of the requirements of the STC are fo llowed in detail. Servicing an air-craft with automotive gasoline without the proper STC is a violation of the Federal Aviation Regulations.

Jet Fuels There are two basic types of fuel used in turbine engines: Jet A and Al and Jet B. The designations used to identify these fuels do not relate in any way to the performance of the fuel in the engine.

Jet A is a special blend of kerosine and i the most widely u ed fuel for civilian jet aircraft. Jet Al is a special type of Jet A that contains additives that make it usable at extremely low temperatures. Navy JP-5 fuel is similar to Jet A fuel, and because of its high flash point, JP-5 is the jet fuel carried aboard aircraft carriers.

Jet B is a blend of gasoline and kerosine fractions and is similar to mili-tary JP-4 fuel. which is the most widely u ed fuel for military jet aircraft.

Both types of j et fuel have a higher viscosity than gasoline, which al-lows them to readily hold contaminants. Water is the most prevalent con-taminant, and it can remain entrained in the fuel until the temperature drops enough for it to condense out and forn1 ice on the strainers. An additive. called PFA 55MB, or Prist, may be mixed with the fuel to lower the freezing point of any water that condenses out. In addition to the problem of shutting off

GROUND OPERATION AND S ERVICI'IG

flash point. The temperature to "hich a material must be raised for it to ignite when a flame is passed above it. but it will not continue to burn.

Chapter 10 619

the fuel by freezing on the strainers, the water that condenses from the fuel supports the growth of bacteria. These bacteria form a scum that holds the water against the aluminum alloy of which the fuel tanks are made. This water causes corrosion inside the tank. The additive that lowers the freezing point of the water also acts as a biocidal agent that destroys these bacteria.

Neither gasoline nor jet fuel burn in a liquid state, but vapors of both com-bine with oxygen in the air to form combustible mixtures. Gasoline evapo-rates at a relatively low temperature, but the mixture of vapor and air above gasoline in a storage tank is normally too rich to burn. Kerosine, on the other hand, requires a higher temperature to evaporate and the vapors above a storage tank of Jet A or Jet A-1 normally form a mixture that is too lean to burn. Jet B fuel has some of the characteristics of both gasoline and kero-sine, and it evaporates over such a wide temperature range that its vapors mix with oxygen in the air to form a combustible mixture over a wide range of storage temperatures.

Keros ine has approximately 18,500 Btu of heat energy per pound and weighs 6.7 pounds per gallon. Aviation gasoline has 20,000 Btu per pound and weighs 6 pounds per gallon. Therefore kerosine, with 123,950 Btu per gallon, has a higher heat energy per unit volume than gasoline with 120,000 Rtu per gallon.

Many aviation gas turbine engine manufacturers allow some aviation gasoline to be used in their engines when turbine fuel is not available. The amount of time aviation gasoline can be used is limited for two reasons: the tetraethyl Lead in the aviation gasoline causes deposits to form on the turbine blades, and aviation gasoline does not have the lubricating proper-ties that kerosine has. Using too much gasoline can cause excessive wear on the fuel control.

STUDY QUESTIONS: AVIATION FUELS Answers are on Page 647. Page numbers refer to chapter text.

11 . Two reasons the use of aviation gasoline should be limited in turbine engines are:

a. ----------------------------------------------

b. --------------------------------------------Page 620

12. The reason jet fuel must not be used in reciprocating engines is that it causes ____________________________ .Page618

620 AVIATION MAINTENANCE T ECHNICIAN GENERAL -

13. The viscosity of jet fuel is--------- ---- (higher or lower) than that of aviation gasoline. Page 619

14. Gi ve the color of each of the. e grades of aviation gasoline. a. Grade 80 --------- ---- ---b. Grade 100 ______________ _ c. Grade lOOLL _ _____ _ ______ _

Page 617

15. Aviation gasoline whose antidetonation characteristics are better than those of the reference fuel ( I 00-octane) are rated in . Page 617

16. The antiknock characteristic of aviation gasoline is increased by using ______________ as an additive. Page 618

17. Lead contaminants are purged from the combustion chamber of a reciprocating engine by adding ---------------- to the gasoline. Page 618

18. The heat energy content per gallon of jet fuel is _ _ ___ _ _ ___ (greater or less) than that of av iation gasol ine. Page 620

19. An uncontrol led burning. or explosion. of the fuel-air mixture within the cylinder of a reciprocating engine is called . Page 616

20. Tf its vapor pressure is too high. a fuel will vaporize too __________ (readily or slowly). Page 616

21. Vapor lock can occur when the vapor pressure of the fuel is too ____________ _ (high or low). Page 616

22. The designations of jet engine fuel ________ _ (do or do not) relate to the performance of the fuel in the engine. Page 619

23. In the dual-number rating sy tem for aviation gasoline, I 00/130 aviation gasoline has an octane rating of 100 with a (lean or rich mixture). Page 617

24. Liquid gasoline _ _ _ ____ _ ____ (will or will not) bum. Page 616

GROU:"

622

Aircraft Fueling One of the most important operations performed by flight line personnel is that of fueling aircraft. An engine may be destroyed if the aircraft is serviced with the incorrect fuel, and numerous airplane crashes with their attendant loss of human lives have been attributed to improper fueling.

Precautions must be observed to prevent fire when the aircraft is being fueled and a C02 fire extinguisher must be available. In general aviation op-erations, the person fueling an aircraft is normally the point of contact be-tween the aircraft owner and the operator selling the fuel. For this reason it is important that special care be taken to gain the confidence of the owner hy maintaining a professional appearance and servicing the aircraft in a careful and professional way. Verifying the requested type offuel and the quantity, whether in gallons, liters, or pounds, are always part of safe and professional line service.

When fueling an aircraft, one must be sure that the correct grade of fuel is used. All fuel tanks used on reciprocating-engine-powered aircraft are re-quired to be marked near the filler opening with the word "avgas" and the minimum permissible grade of fuel.

Since it is so extremely important that no jet fuel be used in reciprocating-engine-powered aircraft, special adapters may be fitted into the filler neck of the tank that will not allow a jet fuel nozzle to enter.

Preparation tor Fueling An aircraft must be prepared for fueling by moving it to a well ventilated area and making certain that only electrical circuits necessary for the fueling process are energized. No one should be doing anything in nor on the air-craft that could create a fire hazard, and smoking in the vicinity of an aircraft being fueled is, of course, prohibited.

All solid contaminants and water must be removed from the fuel before it is put into the aircraft tanks. For this reason the fuel is passed through a water separator as the tank truck is being filled. Temperature changes will cause water to condense in partially filled tank trucks, so the fuel should he passed through water separators on the truck any time there is any indication of water being dispensed with the fuel.

If an aircraft is to be fueled from drums or cans, the fuel should be poured into the tank through a strainer-funnel that removes particles as small as five microns. (A human hair has a diameter of about 100 microns.) If no such filter is available, the fuel may be strained through a chamois skin.

Static electricity causes a special danger when fueling aircraft tanks. As fuel flows through the hose a charge of static electricity builds up, and if the hose and the aircraft are not connected together electrically, a spark is likely to jump between the fuel nozzle and the aircraft tank opening. This area is rich

AVIATION MAINTENANCE TECHNICIAN G ENERAL -

with gasoline fumes and the spark is likely to cause an explosion and a fire. If the aircraft is fueled through a chamois skin and funnel, special care must be exercised to ground the chamois through the metal screen in the funnel and keep it grounded until the fuel has stopped flowing. Plastic buckets and funnels must never be used as they do not allow the static charges to flow into the aircraft structure.

The fuel truck must be grounded with a static strap to dissipate any static charges that have built up, and it must be connected to the aircraft with a bonding cable. Before the fuel tank cap is removed, the nozzle should be bonded by plugging the ground wire into the receptacle located near the tank filler opening. See these grounding and bonding locations in Figure 10-7; the numbers represent the sequence of securing the connections.

Over Wing Fueling All small aircraft are fueled from the top of the fuel tank, and most large air-craft have provisions for this method of fueling if pressure fueling equipment is not available.

When fueling an aircraft by the over-wing method, the fuel truck is po-sitioned ahead of the ai rcraft and the bonding wires are attached. The fuel hose is brought over the leading edge of the wing and the bonding wire connected , then the fuel tank cap is removed. Care should be taken to pre-vent the end of the nozzle damaging the bottom of the fuel tank, but the metal of the nozzle should rest solidly against the side of the tank opening to prevent a static electricity-induced spark jumping from the nozzle to the tank. When the proper amount of fuel has been pumped into the tank. the nozzle is removed and its protective cap replaced. The tank cap is replaced and properly secured, then the bonding wire is removed, and the hose is returned to the fuel truck.

Safety and attention to details cannot be stressed too highly. Even the relatively simple task of replacing the fuel cap can be accompli hed improp-erly. Some tank caps have a vent line that is bent to point forward to pick up ram air pressure to slightly pressurize the tank and assist the fuel flow. If this type of cap is installed backwards the tank loses this assistance and the fuel flow will be decreased. Other types of.fuel caps should seal tightly. and if they are improperly installed, the low pressure of the air above the wing will draw fuel from the tank and can force the aircraft to make an unscheduled landing for fuel.

It i important when fueling an aircraft by the over-wing method that fuel not spill on the rubber deicer boots, and that these boots not be damaged by the hose or by the bonding wire.

GROUND O PERATION A:\D SERVICJ\'G

chamois skin. A soft pliable leather from the skin of a chamois, a goat-like antelope.

Chamois skin is used to filter gasoline. Gasoline will pass through it but water will not. Gasoline that has been fi ltered through a chamois skin may be considered to be free of water.

Chapter 10 623

624

Figure J0-7. The proper sequence for artaching the ground wires when preparing an aircraft for fueling

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Pressure Fueling Most large aircraft are fueled by the single-point, or pressure, fueling method. A large hose carried on the fueling truck is connected to an underground fuel hydrant and to the fueling port under the aircraft wing, using a bayonet-type fueling noule such as the one in Figure I 0-8.

At the fueling port there is a fueling control panel which contains fuel quan-tity gages for each tank, fueling valve switches that activate the fueling valves. lights to show the position of the fueling valves, a fueling power switch, and a fuel gage test switch. The maximum permissible fue ling supply pressure and the maximum permissible defueling pressure are marked on a placard at the fueling control panel. See Figure 10-9.

If the selected tank is to be completely fil led, the fueling valve will auto-matically close when the tank is full, but if the tank is to be pattially filled. the valve can be closed by the fueling operator when the fuel quantity gage shows the appropriate amount of fuel is in the tank.

FUELING TEST

POWER GAGES

0 OPEN 0 OPEN 0 OPEN TANK TANK TANK NO. 3 NO. 2 NO. 1 CLOSE CLOSE CLOSE VALVE @ POSITION @ LIGHTS @

Figure 10-9. Fueling COli/rot pane/under the 11ing of a jet transport aircraft

GROU'\D OPERATIO:\ A:\D SER\'ICI'\G

Figure 10-8. International standard bayo-net fueling no~z.le.for single-poilll fueling

underground fuel h) d r a nt. The terminal of an underground fuel ~)~tern installed at many large airports. The fuel truck which has the required pump~. fil ter~. and metering instruments but no storage tank

i ~ connected to the fuel hydrant. and its hoses are connected to the fueling panel of the aircraft.

bayonet-type fueling nozzle. A t) pe of nozzle used to fuel aircraft \\ ith a pressure. or s ingle-point. fue ling system. T he nozzle is connected to the fue ling receptacle in the aircraft and the handles are turned a portion of a turn to lock. it in place.

Chapter 10 625

Defueling When it is necessary to remove fuel from an aircraft tank, the same proce-dures should be followed as are used for fueling. The defueling process must never be conducted in a hangar, but should be done in an area where there is adequate ventilation. The aircraft should be properly grounded to protect against a static e lectricity buildup. The fuel removed from the aircraft should be protected against contamination and identified so it can be returned to the proper storage fac ility.

STUDY QUESTIONS: AIRCRAFT FUELING Answers are on Page 647. Page numbers refer to chapter text.

25. Two bits of information must be marked on the fuel tank for a reciprocating-engine-powered aircraft are:

a. -----------------------------------------b. __________________________________ ___

Page 622

26. If the aircraft is equipped for pressure fuel ing and defueling, two bits of information are displayed at the fueling control panel. These are:

a. -------------------------------------------b. ____________________________________ __

Page 625

27. Water is removed from the fuel carried in a fuel tank truck by passing the fuel through a --------------------------------- before it is pumped into the aircraft. Page 622

28. Before fue l is pumped into an aircraft fuel tank, the fuel nozzle should be electrically connected to the aircraft structure, the fuel truck should be connected to the aircraft, and both the fuel truck and the aircraft should be electrically connected to the . Page 623

29. A fire extinguisher must be readi ly available whe n fueling an a ircraft. The recommended type of extin-guisher uses as the extinguishing agent. Page 622

30. What important precaution should be taken before pumping fuel into a fuel tank by the over-wing method? The fuel nozzle and the a ircraft should be . Page 623

3 1. It _______________________ (is or is not) normally safe to defuel an aircraft in an air-conditioned hangar . Page 626

626 AVIATION M Al TENA;\CE TECIINICIAI': G ENERAL -

Aircraft Movement Because aircraft are designed to fly, their movement on the ground is often awkward and requires careful planning and skill to prevent damage to the aircraft being moved and to other aircraft.

Towing Aircraft When towing an aircraft always use the correct tow bar and attach it the way the aircraft manufacturer recommends. Tail wheel aircraft may be towed by attaching a tow bar to eyes on the main landing gear or by using a smaller tow bar attached to the tai I wheel. The e methods are seen in Figure 10-10. As soon as the movement of the aircraft has stopped, chocks should be placed in front of and behind at least one of the wheels.

A

c

GROU:\'D O PERATIC:-. A:-.D SER\' ICI:\G

Figure 10-JO A. To11 bar .for mming a tailll'heel

aircraft from the main landing gear 8. Toll' barfor mming a wi/11heel

aircraft f rom the tai!ll'heel C. Tow bar for mming a small tricYcle

gear aircrajf by hand

Chapter 10 627

I I I I I

I I I I I

I / ' I

1// ',1 t Taxi signalman -----;J Figure 10-11. When directing an aircrqfl moving into a parking area, the taxi signalman should be in a position that allows him to be seen by the pilot and allows him to see the 1ring tip.

628

When towing a tricycle-gear airplane, the nosewheel scissors should be ei-ther disconnected or set so they will go into full swivel operation (whichever the aircraft manufacturer recommends). If this is not done, there is a good possibility that the tow bar can turn the nosewheel enough to break the steer-ing stops.

Moving large aircraft normally requires a power tug or tractor, and ex-treme caution must be used when starting, stopping, and turning an aircraft with such a power device to assure that no damage is done to the aircraft.

Taxiing When taxiing an aircraft in close quarters such as on a crowded ramp, al-ways have a taxi signalman stationed in such a position that allows a clear view of the nose of the aircraft, the wing tip, and the person in the cockpit or the tug operator. This position is shown in Figure I 0-11. Standard hand sig-nals such as those seen in Figure I 0- 12 should be thoroughly familiar to all those involved in moving the aircraft and should be used to prevent any mis-understanding.

When moving an aircraft at night, the tax i signalman should use lighted wands. Since it is difficult, when using wands, to distinguish between the signal for "stop" and "come ahead," the signal for stop at night is the signal for "emergency stop" made by crossing the wands to form a lighted X above and in front of the head.

When it is necessary to taxi an aircraft into the flight area, radio contact must be established with the ground controller in the control tower, or at some airports, it is permissible to fol low light signals from the tower. The light signals and their meaning are seen in Figure 10-13.

Light color

Flashing green Steady red Flashing red Flashil1g white Alternating red

and green

Meaning

Cleared to taxi Stop Taxi clear of the runway in use Return to starting point

Exercise extreme caution

Figure 10-13. Light signals used to control taxiing aircraft

AVIATION MAINTENANCE TECHNICIAN GENERAL

..

Flagman directs pilot to signalman if traffic conditions require

Stop Come ahead

Start engines Pull chocks

All clear (O.K.) Left turn

Signalman's position

Emergency stop

Insert chocks

Right turn

Figure 10-12. Standard FAA hand signals used for directing an aircraft on the ground

GROCND O PERATJO\ Ai'D S cR\ 1C1:--.c

~>::::1 ....... Signalman directs towing

..

Cut engines

Slow down

Night operation

Chapter 10 629

Start engine

Move back

Take off

Swing tail to right

Engage rotor

Move forward

Landing direction

Swing tail to left

Stop rotor

Move right

Go up

Figure 10-14. Standard hand signals used for directing a helicopter

630 A VIATION M AINTENANCE T ECHNICIAN

Stop

Move left

Go down

-

G ENERAL

Helicopter Movement When directing a helicopter into or out of a parking area, use the standard hand signals seen in Figure 10-14. Be sure to stand in a location that is clearly visible to the pilot and use exaggerated movements that are clear to the pilot.

STUDY QUESTIONS: AIRCRAFT MOVEMENT Answers are on Page 647. Page numbers refer to chapter text.

32. Refer to the figure below. Identify the meaning of each of these signals. a. SignalA: ____________________________________ ___ b. Signa!B: ____________________________________ ___ c. Signa!C: ____________________________________ ___ d. SignalD: ____________________________________ ___

Page 629

..

A 8 c

33. Refer to the figure below. Identify the meaning of each of these signals. a. Signal A: ____________________________________ ___ b. SignalB: ____________________________________ ___ c. SignalC: ____________________________________ ___ d. SignalD: ____________________________________ ___

Page 630

A 8 c

GROUND 0PERATIO\ A\ D S ER\"ICI\ G

D

D

Chapter 10 631

632

Aircraft Tiedown Many aircraft spend almost all of their ground life tied down outside of a hangar. This naturally shortens the life of the aircraft, but in many cases it must be done . It is important that the aviation maintenance technician un-derstand the correct way to secure an aircraft.

Normal Tiedown Most airport flight lines are equipped with either tiedown rings or cables, and the aircraft may be secured with either ropes or chains.

When using ropes, one made of a synthetic material such as nylon or polypropylene is preferred over manila because the synthetics do not shrink when they are wet, as manila does. Use a bowline knot such as the one illus-trated in Figure 10- 15 and do not tie the aircraft to the wing struts, but use the tiedown rings that are installed for that purpose. Allow about an inch or so of movement to avoid straining the aircraft while, at the same time, pre-venting the aircraft jerking against the ropes in the wind.

Figure 10-15. Steps in tying a bowline knot

A VJATION M AINTENANCE T ECHNICIAN G ENERAL -

When using chains and clips to secure the aircraft, do not depend upon the clip, but pass one link of the chai n through another link and use the clip to prevent the link coming out. This procedure is shown in F igure 10-16.

A Correct method 8 Incorrect method

Figure 10-16. \Vhen securing an aircraft ll'ith chains and clips, do not depend upon The clip to susTain a tensile load.

Many airports have two parallel wire cables secured to the flight line ramp. Aircraft are secured to these cables with short lengths of chain that are free to move up and down the cable. This arrangement allows the tiedown chains to always be vertical when the aircraft are tied down.

Figure 10-17. Method of securing aircraft to a 1rire cable on the flight line ramp

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634

Preparation tor Severe Weather When high winds are forecast for the area in which the aircraft is tied down, special precautions should be taken. The aircraft control surfaces should be locked, either from the cockpit or with external locks, as in Figure 10- 18. If a ta il wheel aircraft is tied down facing the wind, the elevators should be secured in the full up position, and if it is facing away from the wind the el-evators should be secured in the full down position . Tricycle gear airplanes should have their elevatOrs secured in a neutral position.

Spoiler boards may be tied to the upper surface of the wing just above the front spar to prevent air flowing over the wing from producing enough lift to strain the tiedowns (see Figure 10-19). These boards can be made of 2-inch by 2-inch lumber with an inch of foam rubber attached to the bottom with waterproof cement. Holes in the boards allow nylon or polypropylene rope to pass through to tie the board to the wing.

Foam rubber

Plywood

Red warning __ .....,, flag

Figure 10-18. Control surface locks should prevent the swface banging in the wind and should have a red streamer attached to help the pilot remember to remove them before flight.

Securing Helicopters If helicopters are to be tied down outside during severe weather, they should be headed into the direction of the strongest forecast wind and positioned at least a rotor-span away from any buildings or other aircraft. The brakes should be set and chocks installed in front of and behind the wheels. The rotor blades should be secured in the manner recommended by the helicopter manufac-turer, and the fuselage should be secured with tiedown ropes or chains to secure ground anchors.

AVIATION M AINTENANCE T ECHNICIAN GENERAL -

2" x 2" Spoiler

1/4" Polypropylene rope

Sponge rubber

Bungee cord

Figure 10-19. A spoiler board tied ro The upper surface of the wing above the front spar will prevent the wind producing enough lift to strain the tiedowns.

STUDY QUESTIONS: AIRCRAFT TIEDOWN Answers are on Page 647. Page numbers refer to chapter text.

34. The proper knot for securing an aircraft to its tiedown with a rope is a _________ _ __ knot. Page 632

35. When a tail wheel airplane is tied down facing the wind, the elevators should be secured in their full __________ (up or down) position. Page 634

36. When a tail wheel airplane is tied down facing away from the wind. the elevators should be secured in their full (up or down) position. Page 634

37. One of the drawbacks for the use of manila rope for tying down an aircraft is the fact that manila rope _________ (shrinks or stretches) when it gets wet. Page 632

GROUi\D OPERATION AND SERVICING Chapter 10 635

Figure 10-20. Jack placement for raising one wheel for wheel or brake maintenance

636

Aircraft Jacking and Hoisting Aircraft Jacking It is sometimes necessary to lift an aircraft on jacks, either a single wheel for brake or wheel maintenance, or the entire aircraft for landing gear mainte-nance or weighing. It is important that any jacking be done in a location where wind cannot rock the aircraft. No one should be allowed inside the aircraft while it is on jacks.

Each type of ai rcraft has specific requirements for jacking, and the manufacturer's instructions must be followed in detail to prevent damage to the aircraft or injury to personnel. Figure 10-21 shows a high-wing, single-engine airplane on jacks. The jack points (A) are aft of the center of gravity of the aircraft and when the ai rcraft is on the jacks, (B) it is nose heavy. To counter this nose-heavy condition, a weighted tail stand (C) must be attached to the tail tiedown ring.

B

c- --

Figure 10-21. Jacking airplanes with the jack points ahead of the aircraft CG requires a weighted Jail stand to be attached to the tailtiedown ring.

AVIATION MAINTENANCE T ECHNICIAN GENERAL -

Ill

Some aircraft require that jack pads such as the one in Figure l 0-22 be in-stalled. In some installations, stress plates must be installed so that the stresses concentrated at the jack pad are distributed through the aircraft structure. Be sure to follow the aircraft manufacturer's recommendations in detail when jacking the aircraft.

All of the jacks used should have some method of locking the strut in its extended position if the hydraulic pressure should leak off. This is normally done with a large nut, or collar, screwed on the threaded jack strut. As the strut is extended, the collar is screwed down to prevent the strut from retract-ing. Some of the smaller jacks have their struts drilled and pins are stuck through the appropriate hole as the strut is extended.

Figure 10-22. Typical jack pad used under the main wing spar of an airplane

Three jacks should be used to raise an aircraft and they should be raised together so it will remain in its level flight position at all times. If it is al-lowed to tilt, there is a possibility that it could slip off of the jacks.

Before lowering the aircraft be sure to remove all work stands and equip-ment that could be struck as the aircraft settles down, and be sure that the landing gear is locked in its down position. Lower all of the jacks together to keep the aircraft level as it comes down.

Aircraft Hoisting It is sometimes necessary to hoist an aircraft rather than lift it with jacks. For example, if an aircraft has been involved in a gear-up landing or if the land-ing gear has collapsed, it is often impossible to get the jacks in the correct position and a crane must be used to raise the aircraft.

When hoisting the aircraft, attach the cables to the hoisting eyes, and if necessary place spreader bars between the cables to keep them directly in line with the hoisting eyes.

STUDY QUESTIONS: AIRCRAFT JACKING AND HOISTING Answers are on Page 647. Page numbers refer to chapter text. 38. It is necessary when installing jack pads on some aircraft that the stress from the pad be evenly distributed

through the structure by the installation of . Page 637

39. A wing jack is prevented from collapsing because of a hydraulic leak by the use of a __________ screwed on the threaded jack strut. Page 637

GROUND OPERATION AND S ERVICI:\G Chapter 10 637

deicing. Removal of ice from an aircraft structure.

ant i-icing. Preventing the formation of ice on an aircraft structure.

638

Aircraft Icing Protection Aircraft operating in winter months are often faced with the problem of tak-ing off in conditions of snow and ice. Test data indicate that ice, snow, or frost formations having a thickness and surface roughness similar to medium or coarse sandpaper on the leading edge and upper surface of a wing can reduce wing lift by as much as 30 percent and increase drag by as much as 40 percent. For this reason all snow, ice, and frost must be removed.

Federal Aviation Regulations prohibit takeoff when snow, ice, or frost is adhering to the wings. It is the responsibility of the aviation maintenance technician to operate the equipment that deices and anti-ices the aircraft.

Small aircraft that have been sitting in the open and which are covered with snow may be prepared for flight by sweeping the snow off with a brush or broom, making very sure that there is no frost left on the surface. Frost, while adding very little weight, roughens the surface enough to destroy lift. An engine heater that blows warm air through a large hose may be used for de-icing, but care must be taken to prevent water that is melted from running down inside the aircraft structure and refreezing.

There are two methods of ice control for large aircraft: deicing and anti-ic-ing, and there are two types of freezing-point depressant (FPD) fluids used: Type I and Type II. Deicing and anti-icing may be accomplished by two pro-cedures: the one-step procedure or two-step procedure.

Deicing is the removal of ice that has already formed on the surface, and anti-icing is the protection of the surface from the subsequent formation of ice. Just before takeoff large aircraft are both deiced and anti-iced.

The FPD fluids used for icing protection are made up of propylene/di-ethylene and ethylene glycols with certain addi tives. These fluids are mixed with water to give them the proper characteristics.

Type I FPD fl uids contain a minimum of 80% glycols and are consid-ered "unthickened" because of their relative low viscosity. Type I fluid is used for deicing or anti-icing, but provide very limited anti-icing protection.

Type II FPD fluids contain a minimum of 50% glycols and are consid-ered "thickened" because of added thickening agents that enable the fluid to be deposited in a thicker fi lm and to remain on the aircraft surfaces until time of takeoff. These fluids are used for deicing and anti-icing, and provide greater protection than Type T fluids against ice, frost, or snow formation in condi-tions conducive to aircraft icing on the ground.

The deicing and anti-icing may be done in either the one-step or the two-step procedure. In the one-step procedure, the FPD fluid is mixed with water that is heated to a nozzle temperature of 140F (60C) and sprayed on the sur-face. The heated fluid is very effective for deicing, but the residual FPD fluid film has very limited anti-icing protection. Anti-icing protection is enhanced

AVIATION M AINTENANCE TECI INICIAN GENERAL -

by using cold fluids. In some instances. the final coat of fluid is applied in a fine mist, using a high trajectory to allow the fluid to cool before it touches the aircraft skin.

For the two-step procedure. the first step is deicing, and heated fluid is used. The second step is anti-icing, and cold fluid is used, so it will remain on the surface for a longer period of time.

STUDY QUESTIONS: ICING PROTECTION Ansll'ers are on Page 647. Page numbers refer to chapter text.

40. Removal of ice after it has formed on an aircraft structure is called __________ _ Page 638

41. Preventing the formation of ice on an aircraft structure is called ___________ . Page 638

42. Deicing is normally accomplished by using _________ (heated or cold) FPD fluid. Page 638

43. The FPD fluid that is best suited for anti-icing is Type ___________ (I or II). Page 638

Engine Operation The Powerplant section of the Aviation Maintenance Technician Series cov-ers the operation of both reciprocating and turbine engines, but in this Gen-eral section we will cover the most important points of starting both types of engines and discuss some of the safety precautions that should be observed during the engine runup.

Reciprocating Engines By far the greatest number of aircraft in the General Aviation fleet are pow-ered by reciprocating engines. While their operation has been simplified over the years, there are still certain procedures and precautions that must be observed when operating them. In this section we will discuss the proce-dure for starting engines equipped with both float carburetors and fuel injec-tion systems.

GROU:\D OPERATION AND SER\'IC!';G

reciprocating engine. A form of heat e ng ine in which the crankshaft is turned b) the linear action of pistons reciprocating. or moving back and fort h. inside the cylinde rs.

Chapter 10 639

hydra ulic lock. A condition that can exist in an inverted reciprocating engine or in the lower cylinders of a radial engine, in which oil leaks past the piston rings in the lower cylinders and fills the combus-tion chambers. If the engine is forced to rotate, the oil-filled cylinders wil l be seriously damaged.

640

Almost all modern aircraft reciprocating engines are of the horizontally op-posed type, and these are the ones we consider in the starting procedures. But there are still some radial and inverted inline or V-type engines fl ying, and these engines require a special procedure for starting.

Radial and inverted engines have some cylinde rs below the engine centerline, and when these engines are shut down oil may seep past the pis-ton rings and into the combustion chambers of the lower cylinders. Before starting these engines that have been shut down for a period of time, the pro-peller should be rotated by hand for at least two revo lutions to be sure that sufficient oil has not seeped into any combustion chamber to form a hydrau-lic lock.

Since oil is essentially noncompressible, if the engine fires when there is an appreciable quantity of oil in any of the combustion chambers, the engine will sustain major structural damage. If there is o il in any of the cylinders, remove one of the spark plugs from the affected cylinder and rotate the pro-peller in the direction of normal rotation to force out all of the oil.

Starting Engines Equipped with Float Carburetors When starting an aircraft engine, first check the fuel and o il supply, and then make sure that there are no obstructions in the inlet air ducts and that the cowling is securely in place. Chock the wheels and set the parking brake, then follow this starting procedure :

Place the fuel selector valve to the tank that you desire to use for the engine run.

Turn the master switch ON to supply power to the starter and the neces-sary instruments.

Check to be sure that the avionics master switch is turned OFF so none of the electronic equipment wi ll be damaged by spikes of induced voltage when the starter is used.

Place the carburetor heat control in the COLD position so the air that enters the engine will be f iltered. When it is in the HOT position, ai r bypasses the air filter and flows around part of the exhaust system to pick up heat.

Place the mixture control in the FULL RICH position since no fuel can flow from the carburetor until air is flowing through the venturi.

Prime the engine to introduce raw gasoline into the cylinders. This fuel allows the engine to start f iring and draw enough air through the carburetor venturi to start the fuel flowing through the carbureto r. Be careful not to over prime it because the excessive gasoline can cause an induction system fire and can wash oil from the cylinder walls and pistons.

Visually check the area around the propel ler to be sure that there is no one in the way, and assure that the area remains clear by calling out the word "Clear."

When you are sure that there is no one in the way of the propeller, place the ignition switch in the BOTH position and engage the starter.

A VIATION M AINTENANCE T ECHXICIAN G E ERAL -

When the engine starts, check for an indication of oil pressure. If there is no pressure indicated on the oil pressure gage within 30 seconds, shut the en-gine down and determine the cause.

If the engine fails to start and you determine that it is flooded. clear it of excessive fuel by placing the mixture control in the CUTOFF position to shut off all flow of fuel to the cylinders. Turn the ignition OFF, open the throttle. and crank the engine with the starter or by hand until the fuel charge in the cylinders has been cleared.

If an induction system fire occurs. try to keep the engine running or keep it turning with the starter to pull the fire into the cylinders. If it cannot be kept running or turning, discharge a carbon dioxide (C02) fire extinguisher into the carburetor air inlet. co~ does not damage the engine. nor does it leave any residue to clean up.

Starting Engines Equipped With a Fuel Injection System Many modern horizontally opposed aircraft engines are equipped with con-stant-flow fuel injection systems. Starting these engines is somewhat differ-ent from starting one equipped with a float carburetor. The prestarting procedure of chocking the wheels. setting the parking brake. checking the fuel and oil. selecting the proper fuel tank. and turning on the master switch and checking that the avionics master switch is OFF, are the same as for an engine with a float carburetor. The differences are seen in these steps:

Place the mixture control in the FULL RICH position and turn the boost pump ON unti l there is an indication of flow on the fuel now meter: then place the mixture control in the IDLE CUTOFF POSITION. This procedure puts gasoline into the cylinders for star1ing but prevents flooding the engine. The flowmeter indicates only when fuel is actually flowing through the in-jector nozzles.

Visually check the area around the propeller to be sure that there is no one in the way, and assure that the area remains clear by calling out the word clear.

When you are sure that there is no one in the way of the propeller. place the ignition switch in the BOTH position and engage the starter.

When the engine starts on the fuel in the cylinders. place the mixture control in the FULL RICH position and check for an indication of oil pres-sure. If there is no pressure indicated on the oi I pressure gage within 30 sec-onds. shut the engine down and determine the cause.

If the engine fails to start and there is a steady flow of fuel from the in-ternal supercharger drain valve. there is a probability that the mixture con-trol was left in the FULL RICH position. rather than being returned to IDLE CUTOFF after the engine was primed. When the mixture control is in its FULL RICH position, fuel flows into the induction system and drains down into the supercharger section and out the drain valve.

GROUND OPER\TIQ\; .-\\D SERVICI"G

flooded engine. A reciprocating engine that has too much fue l in its cylinder~ for it to stm1. or a turbine engine that has so much fuel in its combw,tor~ that it would create a fi rc hazard or a hot

FOD (Foreign Object Damage). This is a common acronym for damage caused by debris such as nuts, bolts, safety wire. small parts. or tools being sucked into an operating aircraft turbine engine. Intlight damage caused by the ingestion of ice or birds is also considered to be FOD.

642

Hand Cranking a Reciprocating Engine All modern aircraft engines have starters, but sometimes the batteries may be dead and the engine must be cranked by hand. Small engines can be safely cranked by hand if certain precautions are observed. but large engines should be left to someone who is experienced in "propping" these engines. It is al-ways far better to charge the battery than to hand crank large engines.

To safely prop a small engine, follow these steps: 1. Move the aircraft to an area where you can stand on level ground with no

rocks or wet grass that could cause your foot to slip. Place chocks in front of and behind the wheels.

2. Place a responsible person in the cockpit to operate the ignition switch and throttle. This person should turn the fuel ON, the ignition switch OFF, prime the engine, set the parking brake, and crack the throttle slightly.

3. Stand close enough to the propeller that you are not leaning into it, and place the palms of your hands on the blade. Don't grip the blade o r curl your fingers over it. This prevents the propeller pulli ng you into it if the engine should kick back or start to run in the opposite direction.

4. When you are ready, call "Contact." The person in the cockpi t checks to be sure that everything is as it should be and replies "Contact" and then turns the ignition switch to the BOTH position.

5. Move the propeller blade down sharply, and with a smooth follow-through action, swing your body away from the propeller. If the engine does not start on the f irst try, do not touch the propeller until you have called "Switch off ' and the person in the cockpit has turned the switch OFF and has replied "Switch is off."

Turbine Engines Turbojet, turboshaft, and turboprop engines are far simpler in principle than reciprocating engines, but far more complex in their actual operation. For this reason, much of the starting procedure is programmed and is automatic in its operation. The steps listed here for starting turbine engines are purely generic. When actually starting these engines, be sure to fo llow the instruc-tions of the aircra ft manufacturer in detail.

Turbine Engine Starting Before starting a turbine engine, be sure that all of the inlet duct and exhaust covers have been removed and that there are no foreign objects in the inlet ducts. Turn the compressor over by hand to ascertain that the engine rotates freely. Make sure that a power source of the proper capacity is connected and ready to supply compressed air or electricity as needed.

AVIATION M AINTENANCE TECIINICIAN G ENERAL -

Be sure that there are no loose objects on the ground ahead of the engine and that the area behind the engine is clear of anything that could be damaged by the hot blast. Figure I 0-23 show the danger areas both ahead of and behind operating turbojet engines.

Distance in feet 200

150

Exhaust

100

125 40K

150 60K 50

200 100K

0

Air intake

Idle

Velocity in knots = K Temperature in F 125 60K

150 100K

200 200K

300 300K

500 500K

Air intake

Takeoff

Figure 10-23. Turbojer engine inrake and exhausrlw::.ard areas (shaded)

G ROUND O PERATION AND SERVICING Chapter 10 643

hot star t. A start of a turbine engine in which the exhaust gas temperature exceeds the allowable li mits.

hung star t. The malfunctioning start of a turbine engine in which the engine starts, but fails to accelerate to a self-sustaining speed.

644

When the start switch is placed in the START position, a series of events takes place that starts the compressor turning. When it reaches the proper speed, the ignition is energized, and then fuel is sprayed into the combus-tors. A proper start is indicated by an indication of oil pressure and an in-crease in exhaust gas temperature within a specified number of seconds after the start switch is closed. The engine should accelerate smoothly to the cor-rect idling speed and stabilize at this RPM.

Improper Starts The sta1ting sequence for a turbine engine is automatic, but it is possible for faulty starts to occur, and when they do, immediate action should be taken to prevent damage to the engine.

No Oil Pressure If there is no oil pressure indication after a turbine engine has reached a speci-fied speed, turn the fuel and ignition off, discontinue the start, and make a thorough investigation to find the cause of the problem.

Hot Start If the exhaust gas temperature (EGT) or turbine inlet temperature (TIT) rises above its allowable limit, the engine is experiencing a hot start. Turn the fuel and ignition off and discontinue the start. An engine can be seriously dam-aged by a hot start, so make a careful investigation to f ind the cause and to determine if any damage has been done. Hot starts are usually caused by too rich a fuel-air mixture. This is the result of too much fuel for the amount of air being moved through the engine by the compressor.

Hung Start A hung, or false, start of a turbine engine is a start in which the engine lights off as it should, but does not accelerate to a speed that allows it to operate without help from the starter. If you encounter a hung start, shut the engine down and determine the reason it did not attain the required speed.

A hung start is often caused by insufficient power to the starter or the starter cutting off before the engine reaches its self-accelerating speed.

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STUDY QUESTIONS: ENGINE OPERATION Answers are on Page 647. Page numbers refer to chapter text.

44. When starting an aircraft engine equipped with a float-type carburetor, the carburetor heat control should be in the (hot or cold) position. Page 640

45. The most satisfactory fire-extinguishing agent for putting out an induction fire in an aircraft engine is - - - - --- - ----- ----.Page 641

46. Oil collected in the lower cylinders of a radial engine can cause a problem known as _ _ _ ______________________ .Page640

47. A horizontally opposed engine equipped with a fuel injection system is primed by placing the mixture control in the position and turning on the boost pump. Page 641

48. A flooded reciprocating engine using either a float carburetor or a fuel injection system can be cleared of excessive fuel by placing the mixture control in the position. Turn the ignition off, open the throttle. and crank the engine with the starter or by hand until the fuel charge in the cylinders has been cleared. Page 641

49. As soon as a reciprocating engine is started, you should check for an indication of _____________ _ .Page641

50. The mixture control of a float-type carburetor should be placed in the-------- -----position for starting the engine. Page 640

51. A turbine engine start in which the engine lights off but does not accelerate to a speed that allows it to operate without help from the starter is called alan start. Page 644

52. A turbine engine start in which the engine lights off but its temperature exceeds the allowable limits is cal led alan start. Page 644

53. The hazard area extends out ahead of an idling turbojet engine for about __________ feet. Page 643

54. The hazard area extends out behind an idling turbojet engine for about _ _ _ _ ___ ___ feet. Page 643

55. A hot start of a turbojet engine is often caused by an excessively------------(rich or lean) mixture. Page 644

GROU '0 OPERATION A:--:D SERVICING Chapter 10 645

Answers to Chapter 1 0 Study Questions I. a. fuel

b. oxygen c. heat

2. A 3. B 4. c 5. D 6. green triangle 7. red square 8. blue circle 9. yellow star

10. more 11. a. Lead deposits form on the

turbine blades. b. A vgas does not have the

lubricating properties of jet fuel.

12. detonation 13. higher 14. a. red

b. green c. blue

15. performance number 16. tetraethyllead 17. ethylene dibromide 18. greater

19. detonation 20. readily 21. high

22. do not 23. lean 24. will not 25. a. the word "A vgas"

b. minimum permissible grade of fuel

26. a. maximum fueling pressure b. maximum defueling

pressure 27. water separator

28. ground 29. C02 30. grounded 31. is not 32. a. stop

b. come ahead c. emergency stop d. cut engines

33. a. go up b. start engine c. stop the rotor d. engage the rotor

34. bowline

G ROU:"\D OPERATION AND SERVICING

35. up 36. down 37. shrinks 38. stress plates 39. collar 40. deicing 4 1. anti-icing

42. heated 43. II 44. cold 45. C02 46. hydraulic lock 47. FULL RICH 48. CUTOFF 49. oil pressure 50. FULL RICH 51. hung 52. hot 53. 25 54. 100 55. rich

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Chapter 10 647