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Monday, January 23, 2012

EASA Demands A380 Wing Crack Inspections

The European Aviation Safety Agency (EASA) is ordering inspections of relatively high-cycle A380s to assess the extent to which a new set of wing cracks are affecting the Airbus fleet.
The inspections and potential repairs could impact A380 operations, although so far the damage prompting the EASA airworthiness directive has been found only on two of nine aircraft inspected. The culprit is an L-shaped bracket that attaches the wing skin to the ribs.
An Airbus wing expert insists it is not a flight safety issue and that both a short-term fix has been identified in cases where cracking is detected, as well as a longer-term fix to avoid the stress cracks occurring in the future. The cracks have been found on the center section of the wing between the two engines.
The EASA directive addresses a similar parts fatigue problem with wing rib feet brackets initially found on a Qantas A380 and later seen on other aircraft. Those hairline cracks were deemed manageable and could be fixed at C-checks. Those cracks were found because the Qantas aircraft (MSN14) suffered an uncontained engine failure, giving engineers an opportunity to closely examine the wing.
The new cracking is slightly different and viewed as more significant, though. It has been seen on two A380s that have been more closely inspected. Originally, damage was found when a customer aircraft underwent a C-check around ten days ago. One of the brackets, rather than showing hairline stress cracks, on its vertical part had a more significant crack, prompting Airbus to notify safety authorities and also launch a wider inspection of nine aircraft at which point evidence of cracking was found on a second aircraft.
Each wing has around 2,000 L-shaped brackets (30-40 per rib, with 60 ribs per wing), so the failure of one bracket is not seen as a safety issue.
EASA decided to call for an immediate inspection regime rather than waiting for a regular inspection opportunity. Around a dozen aircraft are likely to be affected. The Airbus official notes that even without the extra attention to the issue caused by the findings on the Qantas aircraft, the cracks would have been found during routine maintenance activity well before becoming a safety issue.
Where cracks are found, the bracket has to be unbolted and a new one spliced into the section. Whether that is a permanent fix, or an interim measure is still being assessed.
The inspection is relatively simple, the wing expert says, requiring drainage of the relevant tanks for a visual inspection. However, the time to drain the tanks likely means an aircraft is out of service at least 24 hours, depending on local safety rules. If a bracket is found to have cracked, it needs immediate replacement, which could take a few days.
As part of the root cause analysis, Airbus instrumented one of its own aircraft to assess whether it had erroneously estimated the loads the wing would see, leading to the cracks. But the aircraft maker determined that was not the case. Instead, it found that the likely culprit is the assembly process, which imparts too much stress on the bracket when the wing skin is attached to the rib. The part itself is not being redesigned, but the assembly process is being changed for the long-term solution.

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