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