How Planes Get Their Pink Slips

Light­ning strikes, ex­treme tem­per­a­tures and en­gine fail­ures: for a pas­sen­ger plane to be able to with­stand all that, ev­ery five years it has to spend a month at the world’s big­gest re­pair garage. World of Knowl­edge watched one be­ing put through its paces

World of Knowledge (Australia) - - Contents -

Why pas­sen­ger planes must be re­built ev­ery five years

The last rays of day­light flicker through one of the big­gest garage doors on Earth. Be­hind this por­tal – more than 200 me­tres long and fully glazed from top to bot­tom – sit three wide-body air­craft, among them a Boe­ing 747, for more than four decades the largest pas­sen­ger plane in the world.

Parked in Bay 10 is an Air­bus A330. The ten-and-a-hal­fyear-old pas­sen­ger plane has ex­actly 50,795 fly­ing hours un­der its wings – equiv­a­lent to it spend­ing 5.8 years in the sky. Over a sim­i­lar pe­riod a car man­ages about 4,000 driv­ing hours – af­ter which, in spite of reg­u­lar ser­vices, it might be ready for the scrap­yard.

This Air­bus, how­ever, only has be­tween a third and a half of its ex­pected use­ful life be­hind it. But can a pas­sen­ger plane re­ally re­main safe and air­wor­thy for such a long pe­riod of time?

“No other mode of trans­port is ser­viced so reg­u­larly,” ex­plains Marc Ladewig from Lufthansa Tech­nol­ogy, the world’s largest aero­plane main­te­nance out­fit. His com­pany car­ries out 1,700 checks a day and en­joys a 10% mar­ket share of this lu­cra­tive mar­ket. “A ba­sic check is per­formed be­fore ev­ery flight, a more thor­ough ser­vice takes place roughly ev­ery two months and a de­tailed in­spec­tion last­ing days or even weeks hap­pens ev­ery other year,” he goes on. “But the crown­ing glory is the D-check, a com­plete over­haul that takes place ev­ery five years: we spend 35,000 man­hours check­ing and re­pair­ing more than 10,000 parts over 32 days. After­wards the plane is like new again. Or even bet­ter than new, be­cause we al­ways in­cor­po­rate the lat­est tech­nol­ogy.”

Why is a car ready for the junk­yard af­ter ten years, while an aero­plane can fly for 25 years and longer?

Ladewig and his col­leagues work on the 60-me­tre wingspan Air­bus around the clock. De­pend­ing on the work re­quired, the cost of its D-check will run to seven fig­ures but de­lays could re­sult in a six-fig­ure penalty. So the ap­point­ment must be seam­lessly ac­com­mo­dated in the works sched­ule. The plane with a list price of $320 mil­lion de­liv­ers the last pas­sen­gers and their lug­gage to Hamburg in the evening and then makes its way to the garage where it is parked and scaf­folded.

Today, on day ten of the check, sev­eral kilo­me­tres of ca­bles wind their way through the skele­ton of the fuse­lage. Some cable har­nesses con­tain hun­dreds of in­di­vid­u­ally num­bered wires. Ev­ery flight-rel­e­vant sys­tem, such as those con­trol­ling the di­rec­tion of flight, must be in­de­pen­dently checked three times. “There are hun­dreds of com­put­ers in the server room un­der the cock­pit, which all con­trol the same flight sys­tems,” ex­plains Ladewig. “Be­cause of this they’re not al­lowed to come from the same man­u­fac­turer in case any soft­ware up­dates prove to be faulty. These could com­pro­mise the sys­tems and put the plane in dan­ger.”

The en­gi­neers even clam­ber into the emp­tied tanks on the wings to in­spect the wiring there.

In around 23 days time the Air­bus will be put through its fi­nal in­spec­tion. En­gi­neers will spend ten hours test­ing all op­er­at­ing and back-up sys­tems. This is fol­lowed by a three-hour con­trol flight in which two pi­lots and two en­gi­neers act out crit­i­cal sit­u­a­tions like a stall or an en­gine fail­ure and ob­serve whether the emer­gency sys­tems re­act. Only once these are com­pleted can the air­craft re­ceive its stamp and be dis­charged.

“In the­ory a plane main­tained in this way can fly for­ever,” ex­plains test en­gi­neer Ste­fan Hansen. “But at some point the re­pairs be­come too ex­pen­sive. And the new, op­ti­mised mod­els sim­ply fly more ef­fi­ciently.”

How do you test a plane crash?

IN­SPEC­TION VISIT Lufthansa tech­ni­cian Marc Ladewig (right) ex­plains how his team checks around 10,000 in­di­vid­ual parts over the course of just 32 days.

SANDBLASTER

Dur­ing ser­vic­ing an en­gine re­veals its past: for ex­am­ple, if the ma­chine has flown reg­u­larly over deserts, stirred-up sand abrades the me­tal. It also dulls the cock­pit win­dow.

POWER UNIT

Each en­gine sucks in around 800 cu­bic me­tres of air per sec­ond (equiv­a­lent to the vol­ume of a large de­tached house). This helps gen­er­ate the enor­mous for­ward thrust.

EX­HAUST

A plane is not a rocket: while the lat­ter is pro­pelled as a re­sult of blow­back dur­ing gas com­bus­tion, the gi­ant ro­tors (left im­age) in an aero­plane en­gine gen­er­ate thrust that pow­ers the plane for­ward. The round open­ing here serves as a dis­charge point for ex­haust gases, and less for propul­sion. Once a month the en­tire en­gine must be in­ter­nally flushed.

EN­DURANCE ATH­LETE

Us­ing a mini-cam­era, en­gi­neers also ex­am­ine the in­te­rior of the 14 ro­tors in the en­gine. De­spite tem­per­a­tures of 1,200ºc in the com­bus­tion cham­ber, and com­pres­sor blades ro­tat­ing at close to the speed of sound, the en­gine man­ages 20,000 fly­ing hours un­til it needs its first over­haul. That’s equiv­a­lent to 2.3 years of con­tin­u­ous op­er­a­tion.

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