Going for broke

by Max Kingsley-Jones, commercial aviation editor

The failure last week of an A380 wing during static testing has left many wondering exactly what it means for Airbus and the A380. It was also an interesting case study in how to manage a potentially damaging story about what is a fairly complex engineering exercise.

The failure happened last Tuesday inside a test hangar in Toulouse, but fairly rapidly the bazaars were buzzing with rumours that something had broken during static testing. The share price of EADS - the Airbus majority shareholder - took a tumble as it was unclear just what the impact would be on the ultra large aircraft programme, which is already six months behind schedule.

But some quick thinking by Airbus enabled the manufacturer to take control of the story, making the unusual step of contacting key trade magazines - Flight International included - to offer "instant briefings" before they rang Toulouse to find out what was going on. Without forewarning, we were thrust into a detailed one-on-one telephone brief on "the completion of A380 ultimate load static testing" from Airbus's executive vice president engineering Alain Garcia.

After outlining some of the mundane details of the test effort, Garcia explained that that the wing had suffered a "rupture" just before the test reached the 1.5 times limit load (LL) target required for certification. "This is within 3% of the target, which shows the accuracy of our modelling," he said, declaring the test a success.

Various journals have reported this as successful "test to destruction", but this is not strictly true. Senior, independent structures experts tell Flight that it is normally the intention to complete the ultimate load tests with the wing intact, and then go beyond the 1.5LL requirement until failure occurs. So last Tuesday's rupture at between 1.45 and 1.5LL was not in the original script.

But it is not a disaster either. Engineers tell Flight that the rupture occurred close enough to the target to be considered a success, and that it should be fairly straightforward for Airbus to validate its calculations with analysis from the test and satisfy EASA that the design meets requirements without need for any major re-evaluation or retest.

As Garcia said, Airbus "played the game" with its weight-saving programme and designed the structure to have "no margin at ultimate load". Had the wing sailed past 1.5LL like the 777's did a decade ago (before failing at 1.54LL), then that would have indicated that the modelling had been too conservative, and that Airbus had built too much unnecessary strength (and therefore weight) into the structure.

The failure of a wing below the 1.5LL target is not unprecedented. The A330's wing failed just below the target during static testing in 1992, and on that occasion Airbus managed to prove compliance through analysis combined with the fact that the aircraft's load alleviation system proved more effective than had been envisaged.

More significant was the problem suffered by British Aerospace engineers two decades ago when, according to one structures engineer, the BAe 146 wing ruptured well below the target. The failure is believed to have happened at around 1.3LL and that would have almost certainly required modifications to be validated through a retest. But it didn't stop BAe building 220 146s and another 170 Avro RJs.