Safety authorities call for mandatory wing crack checks of A380s
The (EASA) is ordering inspections of relatively high-cycle to assess the extent to which a new set of wing cracks are affecting the fleet.
The inspections and potential repairs could impact A380 operations, although so far the damage that prompted the EASA airworthiness directive has been found on only 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 the situation is not a flight-safety issue and that a short-term fix has been identified in cases where cracking is detected, as has a longer-term fix to avoid the situation entirely. 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 that was initially found on aA380 and, later, on other aircraft. Those hairline cracks were deemed to be manageable ones that could be fixed during C checks. The cracks were discovered when the Qantas aircraft—(MSN14)—suffered an uncontained engine failure over Batam Island, Singapore, on Nov. 4, 2010. Post-incident examinations afforded 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 were being scrutinized. The damage was spotted when a customer aircraft underwent a C check within the last few weeks. One of the brackets—on its vertical part—had a more significant crack than the original hairline stresses, prompting Airbus to notify safety authorities and to launch a wider inspection of nine aircraft; 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 critical.
Though Airbus's stance is that the problem could have been dealt with during regular C checks, EASA opted for an immediate inspection regime rather than waiting for a routine inspecting point. A dozen aircraft are likely to be affected.
Where cracks are found, the offending bracket has to be unbolted and a new one spliced into the section. Whether that is a permanent or interim fix is still being assessed.
The procedure is relatively simple, the wing expert says, requiring drainage of the relevant tanks for a visual inspection. However, draining the tanks likely means an aircraft is out of service at least 24 hr., 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 the company's original wing load estimates were faulty. It was determined that was not the case. The likely cause was found in the assembly process, in which too much stress is applied to 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 as a long-term solution.
Meanwhile, the Australian Transport Safety Bureau, which heads the investigation into the incident over Batam Island, says the final report for the accident investigation is expected in the third quarter. The agency notes that“has conducted a number of major internal investigations into its processes” covering manufacture of oil pipes with reduced wall thickness; management of retrospective concessions of manufactured components; and failure mode, effects and criticality analysis of previous component failures. That has led to several procedural changes to strengthen risk assessment processes in design and manufacturing.
There are 67 A380s in service with seven operators. Singapore and Emirates operate the largest fleets and also the aircraft with the largest number of flight hours.