Did the airplane’s age play a critical role in the way that Germanwings Flight 9525 flew into a mountain, killing 150 people, without the pilots taking any avoiding action?
Looked at in terms of simple numbers, the Germanwings Airbus A320 was nearing the end of its safe operational life. It was more than 24 years old – but years don’t determine how long an airplane is safe to fly. That is measured by what is called flight cycles: the number of times an airplane takes off and lands.
Airbus A320s of the first generation, as Flight 9525 was, were certified to fly for 48,000 cycles, and, according to the Flight Safety Foundation, the Germanwings A320 had reached 46,700 cycles.
There should still have been a considerable safety margin beyond 48,000 cycles, however, because regulators usually insist that a new airplane can retain its structural integrity for at least double the number of cycles they set as the limit. Part of any test program for a new jet involves taking all key parts of the structure to breaking point.
But that newness also, paradoxically, has another side: in the evolutional history of single-aisle jets, the A320 is still a relatively young design (conceived in the 1980s) that may not have been around long enough to reveal some inherent and still undiscovered weaknesses. For example, its principal competitor, the Boeing 737, has evolved from a 1960s airframe that even now, after many improvements, still has a record of structural weaknesses in its fuselage.
So it is only prudent to include some kind of structural-failure scenario in scrutiny of the Germanwings catastrophe.
And, specifically, there is one very unusual feature of this flight—the fact that the A320 suddenly departed from its cruise height and began a rapid descent lasting, according to French investigators, for nearly ten minutes that never for a second deviated from a course heading directly into mountains. This suggests that the airplane’s flight controls—determining the angle of descent, the direction heading and engine power—were in some way locked into an inescapable, fatal setting.
What could make that happen?
You have to go back to 1985 to find the nearest precedent for a catastrophe of this kind, the case of Japan Airlines Flight 123. This involved a Boeing 747 that had been modified to fly high passenger loads on short inter-city routes in Japan. This meant that its frequent and short flights built up its number of flight cycles far faster than would be usual in the 747’s normal role flying international long haul routes.
In August 1985 one of these modified Japanese 747s suffered an explosive decompression in a bulkhead at the rear of the cabin. The explosion took out the hydraulic system that powered the rudder and the horizontal stabilizers. As a result the airplane became uncontrollable and for 32 minutes it descended in a series of circles until it hit a mountain ridge. Five hundred twenty people on board were killed.
Investigators discovered that the structural failure had been caused by metal fatigue that should have been detected in maintenance checks but was not. The 747 had flown only 18,835 cycles but the unusual stresses of its short-haul schedules had fatally weakened the bulkhead that sealed the pressure inside the cabin at a constant level.
Of course, the significant and extremely puzzling difference between this disaster and the Germanwings crash is that the Japanese pilots remained in full contact with controllers during their heroic but ultimately futile attempts to regain control of the 747 by steering it with changes of engine power. The Germanwings pilots were never heard from, suggesting a more comprehensive structural failure.
Unlike that 747, the A320 was designed from the start for frequent daily flights on short- to medium-distance inter-city routes: the Germanwings jet had flown an average of just over five flights a day during its life. This is typical of the high intensity usage required by budget carriers with short turn-around times between flights. Southwest Airlines, for example, the pioneer of the budget business model, gets as many as seven flights a day from its fleet of Boeing 737s.
The reality is that different parts of an airplane’s structure age at different rates and in different ways. The A320 uses a combination of metal and composites in its construction, each with its own characteristics of ageing and fatigue.
This is why maintenance checks, vital at all times, are particularly critical as an airplane ages. And that is why investigators of the Germanwings A320 crash will be taking a very close look at its recent maintenance records, looking for any record of parts that needed replacing because of fatigue or for anything that might explain a situation that we have really never seen before—that it was that simultaneously locked its flight controls and made it impossible for the crew to send any distress call, finally hitting the mountain with such force that the airplane disintegrated instantly into thousands of pieces spread over a wide area.
