737 classic

AIRCRAFT OWNER’S & OPERATOR’SGUIDE: 737-300/-400/-500

i) Aircraft specifications, page 6ii) Production & fleet analysis, page 8iii) Major modification & upgrade programmes, page 10iv) Maintenance requirements & analysis, page 14v) Values, lease rates & aftermarket activity, page 24

6 I AIRCRAFT OWNER’S & OPERATOR’S GUIDE

The second generation 737-300/-400/-500 family is one of themost popular short-haulworkhorses, particularly for the

growing number of low-cost carriers. Thevarious combinations of gross weight,range and engines of the 737 –300, -400and –500 are detailed in this section.

In total, 1,988 737-300/-400/–500swere built between January 1984 andDecember 1999. Of these, 1,113 were the–300 variant, 486 were the larger –400and the remaining 389 were the smallest–500. The last aircraft built was a -400for CSA Czech Airlines.

The family was launched with entryinto service (EIS) in November 1984 witha -300 for US Airways: line number1001. The airframe shares 80%commonality of spare parts with theearlier 737-200. Other internal changescompared to the -200 include materialsand systems improvements first developedfor the 757 and 767, including an earlygeneration EFIS flightdeck (with fourcolour CRT screens). Soon demand for alarger capacity aircraft, partly as a 727replacement with family commonalitywith the 737–300, led to the introductioninto service in January 1988 of the

stretched –400, which added ten feetaccommodating three extra seat rows.This increased capacity by 19 seats.

The –500 was launched by Southwestand entered service in 1990 to serve someof its less dense point-to-point routes. Ithad almost the same fuselage length asthe -200, which gave it three seat rowsand 18 seats fewer than the -300. The -500’s main appeal is for operators oflarge 737-300 and -400 fleets. Althoughthe -500 is a shortened development ofthe -300, the -500 still carries much of thestructural weight needed for the largermodels. This makes the -500 less efficientthan if it was designed specifically for itssize category. The -500’s extensivecommonality benefits more thancompensate for this, however.

A variety of engine options wereintroduced by CFMI for the -300/-400/-500. The CFM56-3 was launched on the737-300 in its –3B1 variant, initiallyrated at 18,500 lbs thrust. It had thecharacteristic “squashed” engine cowl toaccommodate the fact that it was a high-bypass ratio engine, with a significantlylarger fan diameter compared with thePratt & Whitney JT8D on the earlier737-100 and –200. Two other main

CFM56-3 variants are available atvarious thrust ratings: the –3B2 and the–3C1. There is a degree ofinterchangeability across the family.

There is also an option to installintegral forward airstairs on all 737-300/-400/-500 models.

Specifications

-300 seriesThe –300 model can accommodate

140 passengers in an all-economy six-abreast configuration at a 32-inch seatpitch. This increases to 149 at a higherdensity 30-inch pitch. Major USoperators, like the launch-customer USAirways, configured the aircraft with atwo-class cabin, with eight first class four-abreast seats and 120 six-abreasteconomy seats, totalling 128 passengers.

The initial –300 model has amaximum take-off weight (MTOW) of124,500lbs and fuel capacity of 5,311USG (see table, page 6). This is poweredby the CFM56-3B1 rated at 20,000 lbsthrust. There are two other MTOWvariants for this engine variant. These arethe 130,000lbs MTOW with fuelcapacity of 5,701USG (which is achievedwith a 390USG Boeing-installed auxiliaryfuel tank in the aft cargo compartment)and the 135,000lbs MTOW with fuelcapacity of 6,121USG (using an 810USGBoeing-installed auxiliary tank in the aftcargo compartment).

With the CFM56-3B2 engine variant,rated at 22,000lbs thrust, MTOWsincrease as do fuel capacities, again usingauxiliary fuel tanks in the aft cargo hold.These are MTOWs of 137,000lbs,138,500lbs and 139,500lbs with fuelcapacity of 5,803USG (500USGRogerson-installed auxiliary tank), and6,295USG (1000USG Rogerson-installedauxiliary tank) for the two higher weights(see table, page 6). A derated CFM56-3C1 was also introduced with theseMTOWs in 1988 after the -400 wasmade available.

Range with 128 passengers andstandard fuel is 1,815nm, while rangewith 128 passengers and maximum fuel is2,685nm. The high gross weight versionhas maximum range of 3,400nm with140 passengers.

737-300/-400/-500specificationsThe 737-300/-400/-500 is available with threedifferent engine variants and multiple MTOW &fuel tank options.

There are three main variants. Each can bepowered by engines with two different thrustratings. More than 1,100 aircraft are the -300variant, and nearly 500 are the largest -400variant.

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-400 seriesThe larger –400 model can

accommodate 159 passengers in an all-economy layout at a 32-inch seat pitch.This is achieved with a six-feet fuselageplug insertion forward and another four-feet plug insertion rear of the wing. Seatcapacity increases to 168 at a higherdensity 30-inch pitch. Some major USairlines operate with a two-class cabinlayout, with eight first class four-abreastseats and 138 six-abreast economy seats.

The initial basic –400 model has anMTOW of 138,500 lbs and fuel capacityof 5,311 USG. This is powered by theCFM56-3B2 rated at 22,000lbs thrust,the same engine as the high weight -300.

There are two other MTOW variantsfor this particular 22,000lbs enginevariant. These are the 142,500lbsMTOW with fuel capacity of 5,701USG(which is achieved with a 390USGBoeing-installed auxiliary fuel tank in theaft cargo compartment) and the150,000lbs MTOW with fuel capacity of6,121USG (using a 810USG Boeing-installed auxiliary tank in the aft cargocompartment). The higher gross weightaircraft have strengthened undercarriages.

The higher thrust CFM56-3C1 enginevariant, which entered service inSeptember 1988, and is rated at

23,500lbs thrust, allows MTOWs andfuel capacities to increase. Higher fuelcapacity is again achieved using auxiliaryfuel tanks in the aft cargo hold. Thedifferent versions are MTOWs of142,500lbs, 143,500lbs and 150,000lbs.The first has a fuel capacity of 5,803USG(500USG Rogerson-installed auxiliarytank), and the two higher weights have a6,295USG fuel capacity (Rogerson-installed 1,000USG auxiliary tank).

The CFM56-3C1 can also be de-ratedfor use on the 737-300 and –500. The–3C1 is the most numerous of theCFM56-3 family and superseded the–3B2 and –3B1.

The -400’s standard range withmaximum payload is 2,160nm, whiletypical range with 146 passengers is1,960nm. Their range of the high grossweight option with 146 passengers is2,080nm. Its transcontinental US rangemade it an ideal 727 replacement.

-500 series Originally designated as the 737-

1000, the smaller –500 model is a directreplacement for the 737-200 and canaccommodate 122 passengers in an all-economy configuration at 32-inch seatpitch. This increases to 132 at a higherdensity 30-inch pitch. In a two-class

cabin layout, with eight first class four-abreast seats and 100 six-abreasteconomy seats, but airlines rarely use thisaircraft in this configuration.

The initial basic –500 model has anMTOW of 115,500lbs and fuel capacityof 5,311USG. This is powered by theCFM56-3B1 rated at 18,500 lbs thrust,the same engine as the low weight 737-300. There are two other MTOWvariants for this thrust rating of the –3B1.These are the 124,500lbs MTOW withfuel capacity of 5,701USG (which isachieved with a 390USG Boeing-installedauxiliary fuel tank in the aft cargocompartment), and the 133,500lbsMTOW with fuel capacity of 6,121USG(using an 810USG Boeing-installedauxiliary tank in the aft cargocompartment).

With the same CFM56-3B1 engine,up-rated at 20,000lbs thrust, there aretwo further MTOWs available. The124,500lbs MTOW has a fuel capacity of5,803USG with the 500USG Rogerson-installed auxiliary tank, and the133,500lbs MTOW has a fuel capacity of6295USG with the 1,000USG Rogerson-installed auxiliary tank.

Standard range with maximumpassengers is 1,520nm, while the highergross weight option has a range of2,400nm with maximum passengers.


737-300/-400/-500 SERIES SPECIFICATIONS

Variant -300 -300 -300 -300 -300 -300

MTOW lbs 124,500 130,000 135,000 137,000 138,500 139,500

Fuel volume USG 5,311 5,701 6,121 5,803 6,295 6,295

Engine CFM56-3B1 CFM56-3B1 CFM56-3B1 CFM56-3B2 CFM56-3B2 CFM56-3B2

/-3C1 /-3C1 /-3C1

Engine thrust rating lbs 20,000 20,000 20,000 22,000 22,000 22,000

Seats 128/140 128/140 128/140 128/140 128/140 128/140

Variant -400 -400 -400 -400 -400 -400

MTOW lbs 138,500 142,400 150,000 142,500 143,500 150,000

Fuel volume USG 5,311 5,701 6,121 5,803 6,295 6,295

Engine CFM56-3B2 CFM56-3B2 CFM56-3B2 CFM56-3C1 CFM56-3C1 CFM56-3C1

Engine thrust rating lbs 22,000 22,000 22,000 23,500 23,500 23,500

Seats 138/159 138/159 138/159 138/159 138/159 138/159

Variant -500 -500 -500 -500 -500

MTOW lbs 115,500 124,500 133,500 124,500 133,500

Fuel volume USG 5,311 5,701 6,121 5,803 6,295

Engine CFM56-3B1 CFM56-3B1 CFM56-3B1 CFM56-3B1 CFM56-3B1

Engine thrust rating lbs 18,500 18,500 18,500 20,000 20,000

Seats 108/122 108/122 108/122 108/122 108/122

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Of the 1,988 737-300s, -400sand –500s built, more than1,872 are still in service.Analysis of the fleet shows

that there are a good number of qualityaircraft in operation.

Of the nearly two thousand aircraftbuilt, 1,113 were the –300, 486 were thelarger –400 and 389 were the smallest–500. There are 1,045 -300s active, 467 -400s active and 360 -500s active.

Of the stored aircraft, 50 are -300s,only five are -400s and 26 are -500s.Most of the stored -300s are UnitedAirlines aircraft, with between 40,000 to45,000 flight hours (FH) and 26,000 to30,000 flight cycles (FC). They are allCFM56-3C1 powered and have amaximum take-off weight (MTOW) of130,000lbs. The stored -400s have a totaltime of about 35,000FH and 20,000FCand are lessors’ aircraft. The stored -500sare mainly United aircraft again, and aresimilarly CFM56-3C1 powered. Theyhave an average time of 35,000FH and25,000FC, and are the 123,500lbsMTOW variant.

The largest fleets of all variants (-300/-400/-500) belong to America West,China Southern Airlines, ContinentalAirlines, Delta, EasyJet, KLM, Lufthansa,

Garuda, Southwest Airlines, THYTurkish Airlines, United Airlines, USAirways and Varig.

Some airlines have already begun toreplace their 737-300/-400/500s with737NGs or A320 family types, althoughthe global 737-300/-400/500 fleet showsno real sign of decline overall. There issome activity in conversion of some olderaircraft to freighters, but there has been asurge in demand for passenger-configuredaircraft over the past year and supply hasdiminished.

-300 series Of the 1,113 737-300 series aircraft

built, 1,045 remain in service. Fifth of theremainder are stored. Most are ex-UnitedAirlines aircraft.

The first -300 built was line number1001, built for USAir, in January 1984.The last to be manufactured was for AirNew Zealand in November 1999: linenumber 3130.

Southwest Airlines has the largestfleet, with 194 aircraft built between1984 (line number 1037) and 1997 (linenumber 2932). The fleet is predominantlypowered by the CFM56-3B1 and has a130,000lbs MTOW and 6,291 US

Gallons (USG) fuel capacity. About halfof these have accumulated more than40,000FH, with the oldest at 65,140FHand 63,612FC. The remainder averageabout 30,000FH and 29,000FC. They areall configured with 137 seats in aneconomy layout.

Half of all active -300s are poweredby the CFM-3B1, with 23% (256aircraft) equipped with the -3B2 and just27% (294 aircraft) with the higher rated -3C1. In terms of seat configurations, 576are in a two-class 120- plus eight-seatconfiguration. Another 288 are in normaleconomy 134- to 140-seat configuration,and 186 are in ultra-high density 148-seatlayout.

The 67 highest gross weight aircraftat 139,500lbs MTOW, powered by -3C1s, are operated largely by Aegean, AirNew Zealand, America West, EasyJet,Southwest and Garuda. These aircraftwere mainly produced after 1990 andinclude some of the first -300QCconversions. Most -300s have lowerMTOW of 130,000lbs to 135,000lbs.

There are large fleet operators andmid-sized secondary operators likeAirasia, bmiBaby, Comair, DBA, FrontierAirlines, GOL, Hainan, Jetconnect,Norwegian Air Shuttle, Pace Airlines,PIA, Philippine Airlines, Rio Sul,Shangdong Airlines and ShenzhenAirlines. There is also a plethora of smallscheduled airlines and charter operators,or airlines with small sub-fleets.

-300 Freighter By 2005, 52 737-300s had been

converted to freighters, but the numberbeing converted is increasing. Theyoungest aircraft converted was built in1997, and operates with Air Austral.

Pemco completed conversion of thefirst quick change 737-300QC in 2003.Pemco also converts to pure freighters asthe 737-300SF. One major operator isEurope Airpost. Other freighter operatorsinclude Bluebird Cargo (IAI Bedek andPemco -300SF), Channel Express (-300SFfrom IAI Bedek), China Southern/ChinaPost (Pemco -300QC), TNT Airways (-300SF from IAI Bedek) and YangtzeRiver Express Airlines (Pemco -300QC).

Kitty Hawk became the first 737-300SF operator in North America, takingdelivery in early 2005.

737-300/-400/-500fleet analysisMost 737-300/-400/-500s remain in service.Aircraft are in operation with a wide variety ofweight specifications & engine variants.

The majority of 737s are -300s. Half of these arepowered by the CFM56-3B1, while just less than300 are equipped with the -3C1 engine. Many -300s have now reached mature age.

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-400 series Of the 486 737-400 series aircraft

built, 467 are still active. Five of theremainder are stored. The first -400aircraft built was for the now defunctPiedmont Airlines (line number 1487) inJanuary 1988. The last was built almost12 years later in December 1999 for CSACzech Airlines, and remains with it inservice.

USAirways has the largest fleet of -400s. All 46 of these aircraft are CFM56-3B2-powered, have the lower MTOW of142,500lbs, and are equipped with 144seats in a two-class configuration. Theseaircraft represent some of the older -400swith total time exceeding 40,000FH and20,000FC. Malaysian is close behindwith 38 aircraft, all with an average totaltime of 27,000FH and 27,000FC.

Other major -400 operators are AirOne, Alaska Airlines, British Airways,CSA Czech Airlines, Garuda, JapanTransocean Air, KLM, Malaysian AirSystem, Olympic, Qantas and THYTurkish. Most of the -400 fleet are‘middle aged’, with two-thirds of the fleethaving a total time of up to 40,000FHand 20,000FC. About a third of the fleetis the high gross weight 150,000lbsMTOW variant, with the other threelower weight variants being equallyrepresented.

Most -400s are powered by theCFM56-3C1. In detail, 383 -400s havethe CFM56-3C1, and 65 have the -3B2.Only 18 have the -3B1 variant, all ofwhich are operated by Alaska Airlines.Most 737-400s are configured in a two-class 144- to 150-seat layout. Only 50 arein the high-density 170 seat, all-economylayout.

Secondary -400 operators includeAegean Airlines, Aerosvit Airlines, AirAlgerie, Air Europa, Air Gabon, BluePanorama Airlines, China XinhuaAirlines, Hainan Airlines, JAL Express,JAT Airways, Lion Airlines, MNGAirlines, TUI Airlines Belgium, and VirginExpress.

Some carriers have started to phasethe -400. Lufthansa has disposed of all its-400s. BA has phased out six relativelyyoung aircraft. Aer Lingus has two of itsoriginal six, both of which are aircraftwith less than 35,000FH and 25,000FC.Malaysian Airlines has reduced its fleetby three aircraft. Its remaining aircraft

have interesting potential for acquisition. Alaska Airlines is to have four of its

737-400s converted to a fixed 70-passenger/four pallet configuration. Oneaircraft will be retrofitted to full cargoconfiguration. The aircraft will replacethe airline’s retiring 737-200s.

-500 series The smallest of the classic 737s, the -

500, was introduced as the last memberof the family. Of the 389 737-500 seriesaircraft built, 360 are still active. Of theremainder, 26 are stored or inactive.

The first -500 aircraft built was forSouthwest Airlines, line number 1718, inMay 1989. The last was line number3116, built in June 1999. Most -500shave stayed with their original operator.

Because it is a shrink of the original -300, the trip costs of the -500 are thelowest for the family. These make it anattractive aircraft for small operators, orstart-ups, which wish to take a lower riskon filling aircraft on new or thin routes. Itis also a good aircraft to serve point-to-point routes in markets like the US.

The largest fleet of -500s by far isContinental Airlines with 64, all of whichare currently active. Half are fitted withthe lower rated CFM56-3B1 engine andthe remainder have the newer, higherrated CFM56-3C1. They are all the lowgross weight basic version with a MTOWof 115,500lbs, and have a 5,307USG fuelcapacity and 104-seat, two-classconfiguration.

They were all built after December1993 and have an average total time ofabout 30,000FH/23,000FC. Aircraftrange from 16,000FH/9,000FC up to31,500FH/16,500FC.

United has the next largest fleet, with

38 of the heavier 123,501lbs MTOW -3C1 powered variant, again with a 104-seat, two-class layout. These all have atotal time of about 37,000FH/27,000 FC,and six are in storage. Four of United’saircraft have been sold to Canjet Airlines.

Other large -500 fleets are with AirFrance, All Nippon Airways (ANA), BA(all used), China Southern Airlines, CSACzech Airlines, Lufthansa, SAS Norway(Braathens) and Southwest Airlines.

Airlines that have phased them out, orare beginning to phase them out, are SASNorway (Braathens), Maersk andMalaysian.

There are 111 aircraft with the lowestMTOWs between 108,000lbs and115,500lbs. Another 211 aircraft haveintermediate MTOWs between116,500lbs and 124,500lbs. There areanother 62 aircraft with highest MTOWsbetween 127,500lbs and 133,500lbs.

One-third of the -500 fleet areequipped with the lowest thrust CFM56-3B1, and two-thirds with the highestthrust -3C1 variant. Only three ANAaircraft have the CFM56-3B2.

Secondary -500 operators includesmall regional carriers and some start-uplow-cost carriers in Europe. The -500also forms a small part of larger mixed737 fleets. Operators include AerolineasArgentinas, Air Baltic, Bmibaby,Britannia Airways, DBA, Estonian Air,Garuda Indonesian Airways, Hapag-Lloyd Express, LOT Polish Airlines,Luxair, Maersk Air, Royal Air Maroc,VARIG and Xiamen Airlines.

While not many are readily available,there are a number of low- to middle-aged aircraft that would be interesting forstart-up or small airlines increasingaircraft size. CFM56-3C1-poweredaircraft are most attractive.


There are almost 500 active -400s, and most ofthese are powered with the -3C1 engine. The -400 is the variant in highest demand on theused market.

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AIRCRAFT COMMERCE ISSUE NO. 40 • APRIL/MAY 2005


There is a wide range ofmandatory and voluntaryupgrades and modifications forthe 737-300/-400/-500 that

enhances their operatibility and allowscontinued operation. These modificationsinclude several passenger-to-freighterconversions for the -300 and -400.

Besides conversion to freighter, themain modification and upgradeprogrammes for the 737-300/-400/-500family include: performance enhancementkits; auxiliary fuel tank installations;CFM56-3 engine upgrades; and avionicsinstallations.

Performance enhancement

Aviation Partners BoeingSome of the design work that has

been done for the 737NG family (-BBJ/-600/-700/-800/-900) has benefited theclassic family. Aviation Partners Boeing(APB) has certified the Blended Wingletmodification, originally developed for the737-BBJ business jet and the 737-700/-800, for the 737-300. It is not yetavailable for the -400 or -500.

Aircraft modified with BlendedWinglets carry the SP suffix on theirvariant number to designate for specialperformance. Launched by AirPlusComet on the 737-300 programme, theBlended Winglet received FAAcertification on May 30th 2003. “Weanticipate extensive market penetrationwith our Blended Winglets for the 737-300 and -400,” says Sheldon Best, vicepresident of sales at Aviation PartnersBoeing. “Blended Winglets pay off in fuelsavings, performance improvements andenvironmental benefits.”

“The total block fuel saving benefit ofa 737-300SP is up to 4.5%, about half aper cent better than we’ve achieved with737NGs,” says Mike Marino, chiefexecutive officer at APB. “The average737-300, flying 2,900 flight hours (FH)per year with an average flight cycle (FC)time of 1.5FH, will save over 65,000 USgallons (USG) of fuel per year.”

The environmental benefits ofBlended Winglets include reduced noiseon take-off and landing, decreased engineemissions, and reduced enginemaintenance requirements. Installationrequires a revision to the avionics andflightdeck to install the Load Alleviation

System (LAS) controller and LASspeedbrake auto-Stow mechanism. LAS isnot required for aircraft with an MTOWof less than 125,000lbs. A full suite ofmanual supplements is delivered with theBlended Winglet modification.

The modification is estimated to take2,260-2,360 manhours (MH) and has aspan time of eight to 10 days. The listprice is $450,000 for the 737-300.

Operators look at the wingletmodification for a number of economicreasons, but it also improves performancefrom airports with operating limitations.Another benefit comes from reducedengine maintenance costs. Lower thrustlevels extend on-wing life and reduceEGT margin degradation. Take-off thrustlevels typically are reduced by about 3%and cruise thrust levels by about 4%. Thefinal benefit is higher residual value forthe aircraft, since its operational life islonger than an un-modified aircraft’s.

The main purpose of the BlendedWinglet is to reduce wingtip vortice drag,which reduces fuel burn on all phases offlight. The largest fuel savings are madewith the longest stage lengths. Fleetstudies show that average sector lengthsfor the 737- 300 and -400 are 750-980nm. In both cases, the averagereduction in block fuel is about 3.2%.Fuel burn reduction for longer routes isup to 5%. The 737-300’s fuel burn ofabout 1,550USG for a 750nm trip lengthwill be reduced by about 55USG. Annualutilisations for many US and Europeanand other similar operations generate1,800 flight cycles (FC) each year. Atthese rates of utilisation, total fuel burnsaved will be about 100,000USG, equalto $121,000 per aircraft annually (seetable, page 11). This will allow operatorsto realise a payback from installation ofthe kit in five to six years, based onacquiring the kit at list price.

737-300/-400/-500modification programmesThe 737-300/-400/-500 remains viable for passenger operations. A rangeof performance modifications & engine upgrades are available, in additionto mandatory avionic upgrades and freighter conversion programmes.

There are three performance modificationsavailable for the 737-300. These all reduce dragwith the consequence of reducing fuel burn by 3-5%, depending on modification. At current fuelprices, the cost of these upgrades are paid f0rwithin 18-60 months.

AvAero Performance enhancement

modifications do not all involve majorstructural changes. One provider ofenhancements for the 737 classic family isAvAero from Florida, which offers itsFuelMizer modification. Based uponenhancing the aerodynamic effectivenessof the wing, FuelMizer is an FAA-approved modification for the 737classics, including the freighter version ofthe aircraft. AvAero claims the FuelMizeris the only wing modification for the 737-200, -300, -400, & -500 series designedto improve lift and aerodynamicperformance without costly structuralmodifications. FuelMizer enhances theaerodynamic efficiency of the wing byincreasing the aircraft’s lift-to-drag ratio.By reducing induced drag, a by-productof lift, the FuelMizer modification is ableto deliver typical fuel savings of up to4%. The aft segments of the trailing edgeflaps are relocated aft and below theirstandard locations when in the retractedposition. These changes result inincreased wing area, and airfoil camber,and a lengthened wing chord. AvAerocalculates typical fuel savings of between50 and 80 USG per flight, depending onstage length. A 90 minute flight time andannual utilisation of 1,800FC would saveabout 90,000USG and $107,000 per year(see table, this page). The AvAero kit hasa list price of $135,000.

Importantly there is no change tooperational or flight procedures. Onerecent customer is Kitty Hawk, which haschosen to install the AvAero FuelMizersolution for its 737-300SFs inconjunction with a passenger-to-freighterconversion from Bedek.

Based on test flights with otherairlines, Kitty Hawk expects to realise asmuch as a 4% fuel saving. In typical use,the modification can reduce jet fuelconsumption by thousands of gallons peryear per aircraft.

Quiet Wing Technologies Quiet Wing Technologies Inc has

developed a new noise reduction andperformance kit for the 737-200 and737-300/-400/-500 series. Customershave the option of installing just the wingconfiguration changes for addedperformance (performance kit) or theacoustic treatments and wingconfiguration changes (noise andperformance kit), with the additionaloption of adding winglets to eitherconfiguration for further performanceand fuel savings. The overall effect isimproved operating performance andreduced fuel burn, plus a reduction inaircraft noise, which helps the aircraftachieve Stage 4 compliance.

Total list price for the noise,

performance and winglet kit rangesbetween $295,000 and $645,000,depending on options and the originalconfiguration of the aircraft beingmodified. An additional cost isinstallation. The performance kit alonerequires about 1,200MH, which adds$60,000. Installation of the wingletsrequires a further 600MH, addinganother $30,000.

The reduction in drag relates to areduction in fuel burn through all phasesof flight. Savings in fuel burn are 2-3%for modified aircraft without wingletsand 5-6% with winglets installed.

At an annual utilisation of 1,800FC,the performance kit will save about67,000USG of fuel and about $81,000,while adding the winglets will increasethe savings to 112,000USG of fuel and$134,000 (see table, this page).

It is not yet clear what operatingperformance and payload enhancementsthe 737-300/-400/-500 will gain from thekit, but the additional available payloadand revenue generated will reduce thepayback period for investing in the kit.Kits for 737 classics will be available afterFAA flight testing and receiving STC.

Engine upgrades The initial variant of the CFM56-3

was the -3B1, which was rated at20,000lbs thrust and 18,500lbs thrust.The -3B2 was introduced and rated at22,000lbs thrust, and the -3C1 was ratedat 23,500lbs thrust. These could also bede-rated to lower thrusts, and so the -3C1could be rated at all four thrust ratings.

There are three main upgrade kitsavailable on the CFM56-3 series, all ofwhich improve reliability: a major Time-On-Wing (TOW) extension; an EnhancedPerformance kit; and an Enhanced

Durability kit. These kits improvereliability.

Younger CFM56-3C1s reach morethan 25,000 engine flight hours (EFH)before their first shop visit. Expected first-run life of more than 16,000EFH makethese one of the most durable engines inoperation. Older -3C1s, and -3B2s and -3B1s achieve shorter on-wing intervalsthan the youngest -3C1s.

The first major modification CFMIoffers is the TOW; this is a core upgrade,based on CFM56-7B technology, whichCFMI claims will save up to 1% specificfuel consumption. The kit also increasesexhaust gas temperature (EGT) marginsby about 15 degrees centigrade, therebygiving the engine about 1,500-2,500EFH.The TOW package costs about $1.2million.

The kit features the same advancedthree-dimensional high pressurecompressor aerodynamics (3-D aero) andnew high pressure turbine hardware asthe CFM56-7B. The TOW modificationwas launched by Southwest Airlines in2001 with an order for 300 kits.

Earlier build engines had problemswith the HPT nozzle guide vane andother parts like C-clips. Some earlierbuild engines used X40 material for thehigh pressure turbine (HPT) nozzles ofwhich the nozzle areas tended to openduring operation, causing EGT margin toerode. A new material, DSR142, releasedin 1990, made the nozzles more stable sothat EGT margin deterioration was not asrapid. As earlier build engines have gonethrough shop visits, their older hardwarehas been replaced with younger material,thereby improving their reliability andEGT margin deterioration rates.

Operations, average flight cycle time,route network, and ambient temperaturesall have an impact on the rate of EGT


ISSUE NO. 40 • APRIL/MAY 2005 AIRCRAFT COMMERCE

PERFORMANCE UPGRADE PROGRAMMES FOR THE 737-300

Modification APB AvAero QuietWing QuietWingprogramme Blended FuelMizer Performance Performance

Winglet & Winglet

Kit list price $450,000 $135,000 $400,000 $550,000

Install MH 2,000 250 1,200 1,800

Install cost $100,000 $12,500 $60,000 $90,000

Annual FC 1,800 1,800 1,800 1,800

Fuel burn 4.50% 4.00% 3.00% 5.00%

improvement

Annual fuel 100,800 89,600 67,200 112,000

saving USG

(Average 90 minute

flight time)

Annual fuel saving 120,960 107,520 80,640 134,400

(Fuel at $1.2 per USG)

margin deterioration and time on-wingbetween removals.

The need for performance and lifeimprovement modifications on CFM56-3s therefore depends on the enginevariant and build date, type of HPTnozzle guide vanes, and style ofoperation.

Earlier in 2004, CFMI launched twomore upgrade kits: the EnhancedPerformance kit and the EnhancedDurability kit, giving customers moreflexibility in managing maintenance costs.

The Enhanced Performance kitincludes the 3-D aero HPC blades andvanes, and provides increased exhaust gastemperature (EGT) margin that translatesto as much as 40% longer on-wing life,depending on airline operations.

The Enhanced Durability kit reducespart scrap rates by 50%, therebyreducing maintenance costs. This kit isavailable now and CFMI has receivedfour orders to date. KLM has ordered 31Advanced Upgrades and Air China five.

Freighter conversion The 737-300SF/-400SF (Special

Freighter) and QC (Quick Change) areideal successors for the 727-100 and 737-200. The 737-300SF/-400SF have anidentical fuselage cross-section to the727-100/-200, allowing them to use thesame pallets and containers. There arethree main freighter conversionprogrammes for the 737-300/-400. Thereis no freighter conversion available forthe -500. Conversions are offered by BedekAviation in Israel, by Pemco, Alabama inthe US, and by Boeing Airplane Serviceswith the aircraft modified either byGoodrich in the US or InterContinentalAircraft Services (ICAS) in Taiwan.

Bedek Aviation Bedek launched its conversion

programmes for the 737-300 in June2001, with a launch order from GECapital Aviation Services (GECAS) toconvert 15 aircraft to a Special Freighter(-300SF) configuration. Bedek’sadditional 737-300 conversion programis the 737–300QC (Quick Change).

The conversions have received theirSTCs from the leading aviationauthorities (FAA, EASA, UK CAA andothers). The 737-300SF received its STCin September 2003, and the 737-300QC(‘Quick Change’) received its STC inApril 2004. The 737-400SF/QC STC isexpected in the last quarter of 2006. Theprice for standard 737-300 conversionfrom Bedek is less than $3 million.

The 737SF conversion requires a 60-day cycle, and Bedek operates more thanone conversion line. The conversionconsists of removing all passenger-relatedinterior items and associated wiring, andinstalling of freighter liners.

Floor beams are fitted as required tomeet cargo load requirements, includingthe additional pallet (60.4-inch X 79-inchX 64-inch or 60.4-inch X 96-inch X 64-inch) in the rear position.

There are three standard 737-300SFmaindeck cargo configurations. One mainoption is eight 88-inch X 125-inch X 82-inch containers plus one 60.4-inch X 96-inch X 64-inch container (see table, thispage). Each of the main containers has atare weight of 476lbs and internal volumeof 440 cubic feet. The nine containerstherefore have a total tare weight of4,308lbs and volume of 3,672 cubic feet(see table, this page).

The specification weights are:maximum take-off weight (MTOW)

139,500lbs; maximum zero fuel weight(MZFW) 109,600lbs; maximum landingweight (MLW) 113,600lbs; and operatingempty weight (OEW) 66,500lbs. Exactweights will differ for each customisedconfiguration. This gives the aircraft agross structural payload of 43,100lbs. Anallowance of 500lbs for crew weightshould be given.

The aircraft also has a lower deckvolume of 1,068 cubic feet, taking totalvolume for freight to 4,740 cubic feet (seetable, this page). The crew weight andtare weight of containers give the aircrafta net structural payload of 38,562lbs.

This volume allows a maximumpacking density of 8.2lbs per cubic foot.With freight packed at 7.0lbs per cubicfoot, the aircraft has a volumetricpayload of 33,180lbs.

Pemco Pemco World Air Services is the other

main provider of 737-300 passenger-to-freighter modification.

Following Pemco’s modification, theaircraft will have an MZFW of109,600lbs. OEW varies with conversion,with an average weight of 68,298lbs. Thisgives the aircraft a gross structural payloadof 40,802lbs (see table, this page).

The maindeck has capacity for eightstandard containers and a smaller ninthcontainer, with an internal volume of 152cubic feet and tare weight of 230lbs.Total maindeck volume is therefore 3,672cubic feet (see table, this page). Thesenine containers have a combined tareweight of 4,038lbs, which takes the netstructural payload to 36,264lbs (seetable, this page). The aircraft also has1,068 cubic feet of space below themaindeck, taking total freight volume to



PAYLOAD CHARACTERISTICS 737-300SF/-400SFAircraft Pemco Bedek Boeing

Aircraft Bedek Pemco Boeing Boeingtype 737-300SF 737-300SF 737-300SF 737-400SF

MZFW-lbs 109,600 109,600 109,600 113,000

OEW-lbs 66,500 68,298 68,100 71,050

Gross structural payload-lbs 43,100 40,802 41,500 41,950

Crew weight-lbs 500 500 500 500

Number maindeck containers 8 +1 8 + 1 8 9

Type maindeck containers 82/88/125 82/88/125 82/88/125 82/88/125

Unit tare weight maindeck containers-lbs 476/230 476/230 476 476

Unit volume maindeck containers-cu ft 440/152 440/152 440 440

Total tare weight maindeck containers-lbs 4,038 4,038 3,808 4,284

Total volume maindeck containers-cu ft 3,672 3,672 3,520 3,960

Lowerdeck volume-cu ft 1,068 1,068 1,068 1,376

Net structural payload-lbs 38,562 36,264 37,192 37,166

Total volume-cu ft 4,740 4,740 4,588 5,336

Maximum packing density-lbs/cu ft 8.24 7.65 8.10 7.00

Volumetric payload @ 7.0lbs/cu ft 33,180 33,180 32,116 37,352

4,740 cubic feet. The aircraft can thushave a maximum packing density of7.65lbs per cubic foot. Freight packed at7.0lbs per cubic foot generates a volumetricpayload of 33,180lbs.

In October 2003 Pemco completedconversion of the first 737-300QC. “TheQC aircraft is designed to providemaximum utilisation and revenue byallowing passenger use during the dayand cargo operations at night,”comments Hal Chrisman at Pemco WorldAir Services. “China Southern is a majorcustomer for the QC. The first two 737-300 aircraft being delivered to ChinaSouthern will be QCs and the next twowill be all-cargo aircraft. All four 737-300s are leased from GECAS.”

Passenger seats in the 737-300QCaircraft can be removed within 45minutes, so that the aircraft can beavailable for freight operations. Seats canbe quickly locked back into place andready for passenger service.

“Converted aircraft will be equippedwith all of Pemco’s latest upgrades,including the Pemco redesigned maincargo door,” says Chrisman. “Thesefeatures are unique to Pemco, andincrease aircraft dispatch reliability andreduce maintenance costs.” Each QC canaccommodate eight cargo containers witha payload of about 38,000lbs, while the737-300SF can carry nine cargo containerswith a capacity of up to 40,000lbs.

Boeing Airplane Services Boeing has entered the conversion

market in a teaming agreement withGoodrich and ICAS, offeringmodifications for the -300SF and -400SF.

Under the agreement, all threecompanies worked together in apartnership to develop a 737 passenger-to-freighter conversion program. ICAS isan alliance of major Taiwanesecompanies, including Air Asia, ChinaAirlines (25%), Evergreen AviationTechnologies, and Aerospace IndustrialDevelopment Corp. They are alsomembers of Boeing Airplane Services’international network of modificationand engineering facilities. A QC option isalso being evaluated.

Under the agreement, the partnershipis led by Boeing Airplane Services, whichwill provide proprietary data andtechnical expertise. The STC is owned byBoeing, ensuring that customers canobtain round-the-clock support from the

Boeing global network of Field Servicerepresentatives.

ICAS and Goodrich perform aircraftmodifications at their facilities in Taiwanand in Everett in the US.

The -300SF modification carries eightmaindeck 88-inch x 125-inch pallets,providing 3,520 cubic feet of maindeckpalletised volume and 1,068 cubic feet ofbulk volume in the lower cargo hold.This takes total available volume to4,588 cubic feet (see table, page 12).

The specification weights are: MTOW139,500lbs; MLW 116,600lbs; MZFW109,600lbs; and OEW 68,100lbs.Maximum structural payload is41,500lbs. Deducting tare and crewweight, the aircraft has a net structuralpayload of 37,192lbs (see table, page 12).This gives the aircraft a maximumpacking density of 8.10lbs per cubic foot.

For the -400SF, there are ninemaindeck pallets providing a volume of3,960 cubic feet. Combined with 1,376cubic feet of bulk volume in the lowercargo hold, the aircraft’s total availablevolume is 5,336 cubic feet. Thespecification weights are: MTOW143,500lbs; MLW 121,000lbs; MZFW113,000lbs; and OEW of 71,050lbs.Maximum structural payload is41,950lbs. The container tare weightgives the aircraft a net structural payloadof 37, 166lbs (see table, page 12).

Avionic upgrades There are various avionics upgrades

that 737 -300/-400/-500 owners andoperators need to consider.

The following modifications aremandatory on all aircraft in Europe. Twosets of VHF communication transceiversmust be installed an operational with

8.33kHz frequency spacing above FL245. Traffic collision avoidance systems

(TCAS) have already been mandated.Terrain awareness and warning systemsare also mandatory, currently known asenhanced ground proximity warningsystems (EGPWS), but this requirement isexpected to expand with technology.

Reduced vertical separation minima(RVSM) is mandatory in Europe andAtlantic ocean areas to support highertraffic densities.

The basic form of area navigationrequirements (B-RNAV) is mandatory inEurope, with precision (P-RNAV)optional for now, but will soon berequired to fly into major airports in thenear future with preferential slots.

Mode-S transponders are alsomandatory, with the Elementary andEnhanced Surveillance becomingmandatory in 2007.

Requirements differ in NorthAmerica. As with Europe, 8.33kHzfrequency spacing and 25kHz frequencyspacing are mandated. TCAS mandatoryeffectivity was extended to January 2005and EGPWS also became mandatory in2005. Mode-S transponders aremandatory as in Europe.

Requirements vary widely outsideEurope and North America, making itdifficult to generalise. Radio spacing,TCAS and EGPWS are either mandatoryalready or in progress.

Typical costs for mandatory avionicsmodifications per aircraft are as follows:VHF radio spacing requires parts andwiring modification and costs about$110,000 and uses about 50 man-hours(MH), RVSM is typically $30,000 and30MH, EGPWS/TAWS is about $80,000and 100MH, and TCAS and Mode-S is$250,000 and 800MH.



A small number of 737-300s have beenconverted to freighter. STCs will be available for -400 conversions from late 2006. Marketforecasts predict about 250 737-300/-400s willbe converted to freighter over the next 20 years.


The 737-300/-400/-500 wasdeveloped with a maintenancesteering group 2 (MSG2)maintenance programme. Some

airlines have bridged the aircraft on to anMSG3 maintenance programme. The737’s maintenance requirements includeline maintenance, base airframe checks,heavy component repair and overhaul,line replaceable unit (LRU) rotablecomponents, engine maintenance andspare engine support.

This analysis considers the 737-300/-400/-500’s maintenance requirements andoverall maintenance cost budget foraircraft operated at an average flight cycle(FC) time of 1.25 flight hours (FH) and atypical utilisation of 2,500FH and2,000FC per year.

Maintenance programme The 737-300/-400/-500’s line

maintenance programme is standard withall other aircraft types. It has a pre-flightcheck performed before the first flight ofeach day, a transit check prior to allsubsequent flights during the day and a

daily check performed every 24 hours.Most 737s are operated on short-hauloperations during the day and so dailychecks are performed overnight in mostcases.

The 737-300/-400/-500 has a basic Acheck interval of 250FH, and four Acheck multiples of 1A, 2A, 4A and 8Aitems. These can be grouped into blockchecks or equalised.

When grouped into block checks theA8 check is the heaviest and completesthe cycle at an interval of 2,000FH. TheA1, A3, A5 and A7 checks have just the1A tasks, while the A2 and A6 checkshave the 1A and 2A tasks. The A4 checkhas the 1A, 2A and 4A tasks, while theA8 has all four multiples.

Air New Zealand EngineeringServices (ANZES) has a system underwhich it performs its A checks asequalised checks, which are further splitto allow checks to be fitted into overnightmaintenance slots.

The 737-300/-400/-500’s maintenanceplanning document also has a similarblock check system for C check tasks.The basic C check interval is 4,000FH,

and so two A check cycles are completedevery C check interval.

The C check items are packaged intothe 1C, 2C, 4C, 6C and 8C items, as wellas the structural inspection (SI) tasks.“There are two ways these tasks can begrouped into a system of checks,”explains Li Qiang, manager ofengineering subdivision at Ameco Beijing.“There can be a system of eight checks inthe C check cycle, with the 6C and SItasks being performed in the C6 check,and the 8C items in the C8 check. Thismakes two heavy checks. The 1C, 2C and4C tasks are performed at theirappropriate intervals, so that the C1, C3,C5 and C7 checks have the 1C tasks, theC2 check has the 1C and 2C items, andthe C4 has the 1C, 2C and 4C tasks. Thisway the 6C and SI items get out of phasewith all the other tasks, since the 6C andSI items will be performed again at thetwelfth C check, or the fourth C check inthe next C check cycle.

“The other system that can befollowed is that 7C and 8C tasks arebrought forward to the C6 check and thecycle is completed at this check,”continues Qiang. “This sixth checkwould have all the heavy tasks and istermed the ‘D’ check.”

ANZES operates the system ofcompleting the C check cycle with theheaviest check at the C6 check. “Our Ccheck has a basic interval of 4,500FH,4,000FC and 15 months, whichever isreached first,” explains Viv de Beus,customer support manager for ANZES.“Considering that most aircraft achieveabout 2,500FH per year, about 3,000FHare accumulated in the 15-monthinterval. This means the full C check cycleis completed about once every 85-90months (about seven years) and every18,000-19,000FH, rather than themaximum interval of 27,000FH that isallowed by the basic C check’s FHinterval. We operate a block checksystem, so the checks vary in size, withthe C4 and C6/D checks being the largest.The C1, C3 and C5 checks just have the1C items and so are the smallest.”

Some operators have modified theirmaintenance programmes, and evenbridged to an MSG3 system. KLMoperates 14 737-300s and 13 -400s. “Wechanged our fleet to an MSG3 in 2004,”says Ton de Geest, project engineermaintenance programs at KLMEngineering & Maintenance. “We did

737-300/-400/-500maintenance analysisThe 737-300/-400/-500 have competitivemaintenance costs for aircraft in their size class.Careful management of maintenance costs willensure the aircraft remain economic.


The 737-300/-400/-500’s line maintenanceprogramme results in labour and material costsin the region of $290-355 per FH, not includingsupply of LRUs.

this in conjunction with a Boeingworking group. The main difference to anMSG2 programme is that an MSG3system allows the operator to group eachtask into checks that suit its operation.This means tasks with escalated intervalscan keep their escalations, while otherscan be re-grouped into new checks. Wehave pre-flight, transit and overnightchecks in our line maintenanceprogramme like all other operators, aswell as out-of-phase tasks that are eitheradded to overnight checks or performedseparately. We have an A check intervalof 550FH, and basic C check interval of4,000FH, 4,000FC and 18 months.”

“The new MSG3 programme haseffectively re-arranged tasks, deleted someand added others. The MSG2 programmehad separate structural items andcorrosion prevention and controlprogramme (CPCP) items, as well asothers,” explains de Geest. “These havebeen re-arranged and an enhanced zonalprogramme has been added to the MSG3system. The number of tasks overall hasbeen reduced. In the meantime we havetransferred the fleet to a new schedule inthe MSG2 system where we have a basecheck cycle of six C checks. We had aproblem in that some structural tasks haddifferent initial and repeat intervals,which got more frequent as the aircraftgot older. This meant checks weregradually getting heavier and lesspredictable in terms of content. The newsystem has all structural itemsconcentrated in the 3C and 6C checks,and the 1C, 2C, 4C and 5C checks arelight. These four are all similar in content,while all the structural tasks have thesame intervals. The system means thatevery third check is a heavy check, with

an interval of 54 months (four and a halfyears). This system should result in lessoverall MH per heavy-check cycle thanthe previous block-check system whichwas more complicated. This is becauserepetition of access required duringlighter checks is avoided, and is onlyrequired during heavy checks. The 3Cgroup of tasks, however, actually hassome CPCP items that have an interval of48 months. We therefore adjusted the C3interval to 48 months, and the C6interval to 96 months (eight years).”

The 737-300/-400/-500 fleet was builtbetween 1984 and 1999, and so aircraftare now between six and 21 years old.The base check interval of about sevenyears means that most aircraft will nothave had more than two D checks andwill be in either their first or second basecheck cycle.

Line maintenance On the basis of an aircraft operating

for 350 days per year and completingabout 2,000FC, about 350 pre-flight and350 daily checks will be performed eachyear. A further 1,650 transit checks willbe completed annually, and if weeklychecks are included in the maintenanceschedule then about 50 will be performedeach year.

The number of MH used andconsumption of materials andconsumables for all of these checks canbe totalled and compared to annualutilisation to provide a cost per FH forramp checks.

MH and material consumption for Achecks can also be analysed on the samebasis. The length of the A check cycle interms of calendar time will depend on the

A check interval and number in the cycle. As an example, ANZES has a phased

A check interval of 250FH. Because of adaily utilisation of about 7FC, the actualinterval it achieves between A checks islikely to be about 125FC. On this basisthe number of ramp and line checksperformed in the complete A check cycleis similar to the number completed in ayear.

Estimations of MH used during rampchecks vary widely between operators.This is due to variations in how linemechanics’ hours are recorded, howextensively the aircraft are cleaned andhow defects are addressed. The MH usedto have the most influence on the totalnumber of MH consumed in the completeA check cycle. “Pre-flight and transitchecks consume a similar number of MH,which total about 2.0,” says de Beus.“This is enough for 1.0MH for routineitems and another 1.0MH to coverdefaults arising during operation. Alsoincluded in these MH are generalservicing requirements. The cost ofmaterials and consumables covers itemssuch as oil and water.” An amount whichcan be used for budgeting purposes isabout $15 per check.

“A daily check requires 2.0-3.0MHfor engineering items, and again generalservicing requirements. This is theevaluation of dealing with technical logitems. Cleaning and cabin work will addMH, although this can be done by a thirdparty,” continues de Beus.

Michael Keller, manager ofproduction of engineering and planningat Ameco Beijing estimates that a dailycheck can consume up to an average of13.5MH. Again, the cost for materialsand consumables will be relatively light.Operators can use $50 per check as abudget for material and consumableconsumption for daily checks.

Keller says that material andconsumable cost overall for pre-flight,transit and daily checks can total about$7 per FH.

Some operators include weekly checksin their line maintenance schedules tocomplete out-of-phase tasks. These taskscan also be added to the content of dailychecks.

Over the course of a year, a 737-300/-400/-500 will consume 8,000-10,000MHfor the 2,300-2,400 ramp checkscompleted. This will be equal to aconsumption of 3.2-4.0MH per FH. With



While most operators have retained an MSG2maintenance programme for the 737, KLM hasrecently bridged its fleet to an MSG3 programme.This effectively rearranges tasks and the totalnumber in the programme has overall beenreduced. The system is expected to make thework content of base checks more predictable,and result in less man-hours consumed.

labour for line maintenance charged at anindustry standard of $70 per MH, this isequal to a cost of $220-275 per FH.Consumption of materials andconsumables adds $7-20 per FH, takingtotal cost to $230-295 per FH (see table,page 22).

A checks vary in size and so does theuse of MH and materials. “The blockcheck system we operate has MHconsumptions of about 85MH for A1,A3, A5 and A7 checks,” says Keller. “Thelarger A2 and A6 checks use about125MH, the A4 check consumes about235MH and the largest A8 uses about325MH.”

Ameco’s schedule of an A check cycleof eight checks has an interval of2,000FH, although the actual intervalachieved is likely to be close to 1,600FHconsidering the utilisation of the A checkinterval achieved by most operators. MHconsumption for all eight checks totalsabout 1,150. This is equal to about0.7MH per FH. A labour rate of $70 perMH takes labour cost per FH to $50.Keller estimates the average material andconsumable cost for A checks at about$1,500, totalling $12,000 for the cycleand equal to another $8 per FH. Thistakes total cost per FH for cost of Achecks to about $60 per FH (see table,page 22).

de Beus explains that under ANZES’s1/2 A check system, each half uses anaverage of about 40MH and about $200-500 in materials and consumables.

Although line replaceable units(LRUs) are exchanged during linemaintenance, the capital cost of theseparts and additional charges for repairsand management are accounted for as aseparate item.

Base maintenance checks As described, there are several ways a

base maintenance programme can beorganised. ANZES follows the system ofblock checks, with the cycle beingcompleted at the C6 check. “The totalnumber of MH used in each check in theseries depends on how the programme isstructured, as well as the content,”explains de Beus. “Besides routineinspections and non-routine tasks thatarise as a consequence, several otheritems have to be added. These areairworthiness directives (ADs), servicebulletins (SBs), modifications andengineering orders (EOs), componentchanges such as landing gear or thrustreversers, non-routine repairs tocomponents, interior work, and thesupplemental structural inspectiondocument (SSID) and CPCP. The heavier

checks towards the end of the cycle willhave a higher level of interior work forrefurbishment of panels, lavatories andgalleys. They will also include strippingand painting.”

ANZES manages Air New Zealand’sfleet of 12 737-300, as well asFreedomair’s four aircraft, andJetconnect’s domestic fleet of nine aircraftin New Zealand. “These are aircraft builtbetween the late 1980s and 1999, manyof which are still in or have completedtheir first C check cycle, but have not gotto their second D check,” says de Beus.

Based on a review of severalmaintenance providers, the industryaverage for C1, C3 and C5 checks isabout 5,000MH for the whole content.Only about 1,200-1,500MH of this isused for the MPD element and interiorwork. The remainder is used for ADs,SBs, modifications, EOs and componentchanges and all non-routine maintenance.The check uses about $125,000 formaterials, consumables and somecomponent repair activity.

A C2 check is slightly heavier anduses about 6,500MH when all items areconsidered and in the region of $150,000or materials, consumables and somecomponent repair activity. The C4 checkis one of the heavier checks experiencedby operators, and consumes an average of8,000MH when all items are considered,plus about $200,000 in materials,consumables and component repairs.

Depending on the operator, theC6/C7 or D check is the largest check,and can include some significantmodification packages. A lot of SBs andADs are often completed in these checksso that the aircraft is clear until the nextC check. Average consumption for a firstD check is about 13,000MH plus another1,500MH for stripping and re-painting.The cost of materials, consumables andsome component repairs can vary widely,since the degree to which interior partsand items in the interior are eitherrefurbished or replaced also varies widely.The cost of component repairs is alsohighest in this check, since items such asflap tracks are repaired during thesechecks. A typical range is $300,000-800,000, with an average of $550,000.These checks are also often required foraircraft at the end of a lease agreement,when bridging maintenance and changesto avionics and components are required.

Total MH consumption for basechecks over the first C check cycle isabout 45,000. Charged at an industryaverage labour rate of $50 per MH, totallabour cost is $2.3 million. Total cost ofmaterials, consumables and componentrepairs is about $1.3 million. This totalcost for labour and materials amortisedover the interval of 18,600-20,000FHworks out at an average of 2.4MH perFH, and total cost for base maintenance



checks is $180-195 per FH (see table,page 22).

Ameco Beijing’s C check programmeis similar to that of ANZES. “A total ofabout 15,000MH are consumed for thefirst D check, which includes labour forMPD tasks, engineering orders andmodifications and component repairs,”says Torsten Kurznack, managersubdivision of aircraft overhaul at AmecoBeijing. “Material consumption for thecheck is about $300,000 which is formaterials and consumables, but does notinclude the cost of component repairs.The MH consumed for the second Dcheck will rise over the first, mainlybecause of an increase in the non-routineratio. About 8,000MH will be requiredfor routine and CPCP tasks, aboutanother 5,000MH for non-routine tasks,about 4,000 for EOs and modifications,2,300MH for component repairs andanother 1,600MH for stripping and re-painting. This would be a total of about21,000MH. Total material cost for theseheavier checks has averaged about$550,000.”

Total MH for the second base checkcycle is about 52,000, depending on thenon-routine ratio. This increase, plus arise of total material costs to about $1.6million over the cycle will take totalcharge for the base maintenance cycle toabout $3.9 million. This will be equal toabout $210 per FH.

Heavy components Heavy components fall into four

categories: landing gear, thrust reverser,wheels and brakes, and auxiliary powerunit (APU). These four component typeshave independent maintenance schedules.Apart from the landing gear, all are

maintained on an on-condition basis. Most operators now opt for exchange

programmes for landing gears, which willhave to be used for small airlinesacquiring used aircraft. Maintenanceintervals are 8-10 years and up to32,000FC, and exchange programmes area single cost to cover exchange fee andoverhaul cost. “Exchange costs varywidely depending upon availability, butthey normally include a fixed cost ofoverhaul, “ explains Steve Hodgkiss,managing director of FlyerTech. “Anoverhaul fee of $150,000 is reasonabledepending on condition of the landinggear. Exchange fee will be about $40,000.”

A total cost of $190,000 incurredevery eight years will be equal to a cost of$10 per FH (see table, page 22).

Costs for wheels and brakes arerelated to FC intervals. Wheels requiretyre remoulds and replacement, as well aswheel rim inspections. Tyre removal andre-tread intervals will be affected bylanding weight, which will vary byaircraft variant. Average intervals of250FC for main wheels and 200FC fornose wheels can be expected, and tyresare remoulded an average of three timesbefore being replaced at the fourthremoval. This would make the total life cycleof main and nose tyres 1,000FC and 1,200FC

Re-tread of main wheel tyres has anaverage cost of $400, while nose tyreswill be about $350. New main and nosetyres cost about $1,400 and $800. Totalcost for remould and replacement for acomplete shipset of four main wheel tyreswould be about $10,400, and about$3,700 for a shipset of two nose wheeltyres. Amortised over the replacementinterval, this results in a rate of $13 perFC (see table, page 22).

Wheel inspections are made at tyre

removal and have an average cost of$650 for main wheels and $600 for nosewheels. This results in a cost of $12 perFC (see table, page 22).

Brake repairs are made on averageevery three wheel removals, and so aboutevery 900FC. The average cost for abrake repair is about $11,000, and thecost per FC for all four main wheel brakeunits is $49 (see table, page 22).

Thrust reversers for mature aircrafthave an average removal interval ofabout 8,000FC. A cost of $190,000 foran average shop visit can be used for athrust reverser shipset. The total cost forboth reverser shipsets amortised over theremoval interval is about $48 per FC (seetable, page 22).

The 737-300/-400/-500 uses theGTCP 85-129 auxiliary power unit(APU). Many operators will use the APUwhile taxiing to the gate beforeconnecting to a ground power unit, andthen use the APU again during enginestart. The APU thus gets used twice ineach FC for an average of 45 minutes,and will therefore accumulate about1,500 hours per year. The average timebetween shop visits is about 3,500 APUhours, equal to more than two years ofaircraft operation. An average shop visitcost of $150,000 is equal to $32 per FC(see table, page 22).

Line replaceable components The 737-300/-400/-500 is now

widespread in the global fleet, and thereis a plentiful supply of rotable LRUs onthe used market. Prospective operators of737-300/-400/-500s have several choicesfor sourcing LRUs. Many maintenanceproviders offer LRUs, as do specialistcomponent providers.

The standard practice would be for anoperator to be supplied with a home-basestock and given access to a componentpool for the remainder of the items onceit had established the confidence level itrequired in its operation, what the failurerates of the components are likely to be,as well as the structure of its operation.

Ralf Aljes, manager subdivisioncomponent services at Ameco Beijing saysa small operator can be supplied with anLRU contract at a rate of $110-120/FHto cover the cost of repair andmanagement of the parts, and a further$40-50/FH for access or lease costs of thematerial. “Total cost is $180-220 per FH



The base checks in an MSG2 programmeconsume in the region of 50,000 man-hours forthe second base check cycle. This, and materialcosts, result in an overall cost in the region of$210 per FH.

for the airline if it joins the access pool(see table, page 22). This cost includes therepair and management of parts andaccess to all LRUs. This compares to aprobable cost of $300/FH if an airlinewere to lease its own stock and managethe repair by itself,” says Aljes.

Every rotable supply contract isdifferent, and Hodgkiss says it is possibleto get a contract for about $110 per FH.“This would be the rate for the supplyand repair of all LRUs, without includingwheels and brakes, interior parts andlarge insurance items. It does not includethe cost of shipping all items sent forrepair. The $110 per FH rate includes thesupply of a minimal home-base stockworth about $500,000 for one or twoaircraft,” says Hodgkiss. “Another $50per FH could be added to cover allmiscellaneous and unknown items, suchas cabin items, oil and unscheduledproblems and accidents.”

Engine maintenance There are three variants of the

CFM56-3: the -3B1, -3B2 and -3C1. The-3B1 is rated at 18,500lbs and 20,000lbs,and powers the 737-300 and -500. The -3B2 can be rated at 22,000lbs andpowers all three family members. The -3C1 is the most numerous and can berated at 23,500lbs and all lower thrust

ratings for all three 737 variants. The lower-rated engines have installed

exhaust gas temperature (EGT) marginsin the region of 135-140 degreescentigrade, while those rated at 20,000lbshave margins of about 110 degrees, thoserated at 22,000lbs rated at 70 degreesand the highest powered models havemargins of about 50 degrees.

These margins and the rate of EGTmargin erosion generally allow longremoval intervals between shop visits.Most CFM56-3s built have been throughtheir first shop visit and are on theirsecond or subsequent on-wing runs. Thelowest maintenance cost per engine flighthour (EFH) contributes to lower overallaircraft maintenance costs. Low rates perEFH are achieved by optimising removalintervals, shop visit workscopes and LLPreplacement timing. LLPs can generallybe divided into three groups: in the highpressure (HP) section, the low pressureturbine (LPT); and fan and boostersection. Most HP system LLPs have livesof about 20,000EFC, although a few arerestricted at 15,000-17,000EFC. The listprice for LLPs in this section is about$650,000. LPT LLPs have lives of25,000EFC, and have a list price of about$410,000. Fan/booster LLPs have lives of30,000EFC and list price of $263,000.

The high EGT margins of the lowestrated engines allow on-wing intervals to

average about 18,500 engine flight cycles(EFC). This compares to an annual rateof utilisation of about 2,000EFC, and sois equal to about nine years of operation.HP and LPT LLPs should be replaced atthis stage, since the restored EGT marginafter the shop visit will allow a secondremoval interval of 11,000-12,000EFC.Besides HP LLP replacement, the engineshould require a performance restorationon the core engine and a workscope onthe LPT. This will have an approximatecost of $1.1 million, not including LLPs.

The second run of about 11,000EFCwill be followed by another core engineperformance restoration and workscopeon the fan and booster section, as well asreplacement of fan and booster LLPs.This will incur a cost in the region of$950,000, not including LLPreplacement. The third removal intervalwill be 500-1,000EFC less than thesecond and will be followed by a shopvisit workscope similar to the first atwhich HP and LPT LLPs would bereplaced. This would have a cost of about$1 million, not including LLPs. By thisstage the engine will have accumulatedabout 40,000EFC on-wing, equal toabout 20 years of operation.Maintenance reserves, including LLPamortisation, up to the first removal willbe in the region of $90 per EFH. This willincrease to $110-115 per EFH for the





second removal intervals (see table, thispage) and increases again to about $130per EFH for the period up to the thirdremoval. Subsequent intervals areexpected to be in the region of 9,000-11,000EFC, given the high EGT margin,and $130-145 per EFH should beallowed for maintenance reserves.

Mid-rated engines have planned first-run removal intervals of about11,000EFC, and can be expected to havea subsequent on-wing time of 9,000EFC.It is therefore not necessary to replace anyLLPs at the first shop visit. The first shopvisit workscope is usually a coreperformance restoration, since the LPTand fan/booster sections can remain on-wing until the second removal. The costof this first workscope will be in theregion of $900,000.

The second removal interval of9,000EFC takes total time to about20,000EFC, equal to about 10 years ofoperation, at which point HP and LPTLLPs should be replaced. The shop visitworkscope at this stage is a corerefurbishment and LPT workscope. The

cost for this shop visit, not includingLLPs, is about $1 million. The third andsubsequent on-wing intervals will be inthe region of 8,500EFC.

Maintenance reserves, including LLPamortisation, are in the region of $105per EFH up to the first removal, $125 perEFH up to the second removal, and $135per EFH up to the third removal and asimilar rate thereafter (see table, thispage).

The highest-rated engines naturallyhave the shortest on-wing removalintervals, which are about 8,500EFC forthe first interval. At this point the enginehas a core engine performance restorationworkscope, but no LLPs are replacedsince the engine is capable of a secondremoval interval of about 6,500EFC. Thefirst shop visit workscope is a coreperformance restoration, which will costabout $900,000 not including LLPs.

The second removal interval will beabout 6,500EFC and the engine will havea heavy core workscope, sinceaccumulated time on-wing will notnecessitate work on the fan/booster or

LPT sections. Total accumulated time atthis stage will be about 15,000EFC, andso HP LLPs should be replaced, althoughfan/booster and LPT LLPs can remain forthe third on-wing run. The second shopvisit will cost about $950,000, notincluding LLPs.

Mature intervals to subsequent shopvisits will be 6,000-6,500EFC. Total timeto the third shop visit will be about21,500EFC and the engine will require afull workscope on the core engine andLPT section, as well as LPT LLPreplacement. The cost of this workscopewill be in the region of $1.1 million, notincluding LLPs. Maintenance reserves tothe first shop visit will be about $135 perEFH, climbing to about $180 per EFH atmaturity (see table, this page).

Maintenance cost summary The total direct maintenance costs for

the 737-300/-400/-500 vary between$1,050 and $1,270 per FH (see table, thispage). The actual cost per FH isinfluenced by all elements of maintenancecost, but ramp and line checks, repair ofheavy components, LRU rotablecomponent support and enginemaintenance vary widely. Despite theirmagnitude and attention they attract, thecosts of base airframe checks arerelatively predictable.

The eventual cost per FH for rampchecks will be affected by efficiency oflabour, but also how labour for linemaintenance is recorded and allocated, aswell as an airline’s maintenance practices.

This goes partly in-hand with the costof LRU rotable support, which is alsohighly variable. The ultimate cost per FHfor this element can vary by more than$100 per FH. Engine maintenance costswill be most affected by thrust rating, andconsequently by aircraft variant and grossweight.

The 737-300/-400/-500 are stillpopular, and many are operated byoriginal users, although more aircraft arenow being acquired by secondary usersand are becoming mature. The lastmanufactured aircraft is now six yearsold, and most engines are mature, havingbeen through their first and second shopvisits. Tight control of all these elementscan keep maintenance costs stable.

Spare engine support Operators also have to consider the

costs of spare engine provisioning.Removal intervals for mature engines arein the 7,500-12,000EFH range,depending on thrust rating and style ofoperation. This is equal to three to fiveyears of operation in most airlines’ cases,but will be 30-55 months onceunscheduled removals are taken intoaccount. Typical shop turn times of three

DIRECT MAINTENANCE COSTS FOR 737-300/-400/-500

Maintenance Cycle Cycle Cost per Cost perItem cost $ interval FC-$ FH-$

Ramp checks $600,000-700,000 1 year 230-295

A check $60,000-90,000 1,300-1,600FH 60

C & D checks $3,600,000 18,500-20,000FH 180-195

Heavy components:

Landing gear $190,000 16,000FC 13 10

Tyre remould & $12,000 800FC/1,400FC 13 10

replacement

Wheel inspections $3,800 200FC/250FC 12 10

Brake inspections $44,000 900 49 39

Thrust reverser $340,000 8,000 48 38

overhauls

APU $150,000 4,700 32 26

Total heavy components 167 133

LRU component support 180-220

Total airframe & component maintenance $785-910/FH

Engine maintenance:

High rated (mature) $180/EFH X 2

Mid rated (mature) $135-150/EFH X 2

Low rated (mature) $130-145/EFH X 2

Total direct maintenance costs:

Aircraft with high rated engines $1,145-1,270/FHAircraft with medium rated engines $1,055-1,210/FHAircraft with low rated engines $1,045-1,200/FH

Annual utilisation:2,500FH 2,000FCFH:FC ratio of 1.25FH:1.0FC



to four months mean that one spareengine will support 10-15 installedengines, or a fleet of five to seven aircraft.

This is a small fleet, and airlines withat least this number of aircraft would findit economic to own a spare engine thathad full utilisation in covering forremoved units going through shop visits.Demand for the 737-300/-400/-500 hasincreased over the past year to 18months, following a surplus. A number ofaircraft were repossessed from UnitedAirlines and USAirways. Some werebroken for parts and engines, whichtemporarily brought down values ofaircraft and the CFM56-3s. “The lastpeak in CFM56-3 values was in 1998,and they then reached a trough in 2000-2002,” says Tom MacAleavey, senior vicepresident of sales and marketing at WillisLease Finance Corporation. “CFM56-3values have gone up by 20-25% andthere is now a shortage of them. Theengine is also no longer built and this hasexacerbated the problem. Values mainlydepend on the maintenance status. It cancost nearly $3 million to put an enginethrough a heavy shop visit and replace acomplete set of LLPs. Core values ofcompletely run-out engines are $600,000-700,000. Values of -3C1s fresh from anoverhaul that have LLPs with at least10,000EFC remaining have a value of$3.5-4.0 million. Values of -3B2s are

slightly less at about $3.2 million.” Andrew Pearce, director at Macquarie

Aviation Capital puts values for -3C1sand -3B2s in a good maintenancecondition at a similar level. “A -3B2 freshfrom a shop visit and with fairly goodLLP status has a market value of $3.2-3.45 million. A -3C1 in the samecondition has a value of about $4.0million.”

These values have to be considered inrelation to long-term lease rates thatairlines would alternatively have to pay ifthey did not own spare engines.Maintenance reserves would also have tobe paid with lease rentals. “More airlinesare now taking engines on long-termleases,” says MacAleavey. “Long-termlease rentals have now risen to $40,000-44,000 per month for -3C1s, and areslightly lower for -3B2s.”

Pearce confirms that lease rates havefirmed up to this level over the past 12months. “Maintenance reserves also haveto be paid, and these are about $120 perEFH and $70-80 per EFC,” says Pearce.This equates to a total reserve of $184per EFH for an engine operated at anaverage EFC time of 1.25EFH.

MacAleavey puts reserves at $115 perEFH and $71 per EFC for -3C1s, $84 perEFH and $62 per EFC for -3B2s, and $98per EFH and $62 per EFC for -3B1s.

Most airlines also have to consider

short-term leases for coverage in the eventof unscheduled failures and engineremovals, and emergency requirements.“Short-term lease rentals are in the rangeof $1,800-2,000 per day, plusmaintenance reserves, although they dodrop by about $400 per day in off-peakseasons when airlines are not so busy, “comments Pearce.

Technical support Besides direct maintenance costs,

airlines have to consider having theinfrastructure in place for the technicalmanagement of their aircraft. “This willbe expensive for small and start-upoperators to consider,” says Hodgkiss atFlyertech. “We specialise in providing thistechnical management and can sourcemaintenance providers, set a maintenancecontrol department, and manage thewhole range of technical managementaspects for airlines. This includesmanaging the aircraft’s maintenanceprogramme, determining maintenancetask workscopes, deciding which ADsand SBs to perform, monitoring reliabilitydata, keeping maintenance records, and awhole range of other tasks. The cost forproviding all of these services for a smallfleet will be in the region of $2,500-3,500per aircraft month, and will reduce withfleet growth.”



The 737-300/-400/-500 are tootechnologically advanced toenter a state of decline. Theaircraft are simple to operate

and have been used by the majority ofairlines around the world. There is alsothe fact that there are more than 1,000MD-80s in service that will decline priorto the 737, as well as the overridingfactor that there are few good qualityaircraft in storage.

The age of the 737-300/-400/-500fleet ranges between six and 20 years.The majority of aircraft would thus beconsidered to be at a ‘mature’ age. Themedian age of the fleet and theiraccumulated flight hours and flight cycles,and the presence of the more advanced737NG and A320 families, has putpressure on the market values of 737-300/-400/-500s. Most aircraft haveentered the phase where values havebegun to decline more rapidly.

Values of 737-300/-400/-500sdropped after 9/11 with the ensuing glutof aircraft. “While the values of olderaircraft types have dropped through thefloor, values of good quality 737 classics

have gone up by 30-40% since the post-9/11 trough,” says Doug Jaffe, chiefexecutive officer at Jetran International.There was a surplus of 737-300/-400safter 9/11, mainly because a large numberof ex-United and ex-USAirways aircraftwere parked.

“The supply of 737-300/-400/-500s isnow tight. This is because airlines areswapping out older aircraft, like the 737-200 and MD-80, for younger types. Thisprocess has been intensified because ofthe rise in fuel prices. The price of fuelhas driven 737-300/-400/-500 values upbecause they are the most fuel efficient ofolder generation aircraft,” continuesJaffe. “The 737-300/-400/-500 is alsomuch easier to trade worldwide thansome types. It is hard to get an airoperator’s certificate (AOC) for the MD-80 in Romania, for example. There arestill problems when trading 737-300/-400/-500s across continents, however.Some avionics are mandatory in Europe,but not in the US. This can result in someexpensive modifications being required.”

Jaffe makes the point that if a majoroperator, for example USAirways, were

to cease operations or merge withanother carrier, it might release 40-50aircraft onto the market. “It would stillnot be too difficult to place these aircraftwith airlines, given the demand for them,although it would pull values downagain,” he comments.

The problem with 737-300/-400/-500values is that the CFM56-3 is anexpensive engine to overhaul. “This ismainly because of the price of parts. Anoverhaul can go to as high as $1.5million, which compares to about $1.0million for a JT8D. The maintenancestatus of the engines therefore has themost influence over values of 737-300/-400/-500s. Older -300s, which are mid-life in maintenance terms, have values ofabout $7 million, while younger aircraftbuilt between 1990 and 1999 have valuesin the $9-11 million range,” says Jaffe.This compares to engine values, whichare $3-4 million each, depending onmaintenance status and lives of lifelimited parts. Engines can thus accountfor up to 90% of an older aircraft’s value,and up to 80% of a mid-life aircraft’s.

“Values of -400s are not much higher,with older aircraft being in the $7-8.5million range and mid-age aircraft being$9-12 million,” continues Jaffe. “The -500s are not that popular, but values arenevertheless close to the -300/-400 at $8-10 million. Lease rates are also close forthe three variants, and are $85,000-105,000 per month for earlier buildaircraft and $110,000-140,000 foryounger aircraft.”

While the supply of aircraft has beensoaked up, values have not increased asmuch as lease rates. There are few cashbuyers of aircraft, and most airlinesprefer to lease when liquidity is low.

The 737-300/-400/-500 benefits fromthe fact that the CFM-56s havepredictable on-wing intervals, andalthough they are expensive to maintainthey make the aircraft’s overallmaintenance costs stable.

The rise in values will causeuncertainty in the freight conversionmarket. The accepted market lease ratefor a 737-300SF is in the region of$100,000-110,000, and a lease ratefactor of 1.25% puts the total cost foracquisition and conversion to freighter atno more than $9 million. “This meansthe market for an aircraft can be no morethan about $6 million for someonebuying a used machine and speculativelyconverting it,” says Jaffe. “A lessor thathas fully or nearly depreciated its aircraftcan justify conversion, however.”

737-300/-400/-500values, lease rates &the aftermarketValues of 737-300/-400/-500s have reboundedfollowing a surge in demand.

Demand for 737-300/-400/-500s has liftedmarket values by as much as 40%. Supply ofaircraft is now tight and values are in the regionof $7-11 million, depending on age, variant andmaintenance status.

737 classic

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