There are several causes for the wing-component cracking problem. One is the use of a specific aluminum alloy (7449) and its heat treatment. The alloy saves weight, but it rendered the component more brittle, causing cracking. Another is in attaching the wing skin to the ribs, where excessive loads were placed on components during assembly. The situation was compounded by a failure to properly account for the temperature-induced material expansion and contraction during operations.
EASA still has to sign off on the fix. That will require validating the proposed repair during flight trials using an instrumented Airbus A380 test aircraft, which Williams expects will fly in the fall.
To avoid future problems, Airbus will make changes beyond those immediately needed. For instance, ribs 48 and 49, at the outer end of the wing, will be replaced even though no cracks have been found in them, because they are made with 7449 aluminum alloy. The ribs will be replaced with ones made with a more traditional alloy (7010).
Airbus is discussing with airlines how to phase-in the retrofit on aircraft in operation. Options include parking aircraft for several weeks to fully install the fix or making enhancements through several C checks. The fix comes with a relatively modest 90-kg (198-lb.) weight penalty.
Some airlines may defer aircraft delivery until the permanent repair is installed.
The retrofit entails replacing all of the 23 hybrid ribs (made of a mix of 7449 aluminum and composite) with all-metallic ribs made of 7010 alloy. The rib feet will also be redesigned to strengthen them, and an inspection manhole in the area where the cracking occurs will be strengthened.
The fix should be available on newly built wings in early 2013, which means that aircraft entirely unaffected by the problem will exit the Toulouse final assembly line in 2014.
Meanwhile, Airbus is gradually seeing improvements in dispatch reliability of the A380, although it is still below that of other Airbus products. Reliability since service entry now stands at 97.6%; it rose to as high as 98.6% in March. “It is going in the right direction,” says Airbus COO for customers, John Leahy, of the dispatch reliability. He hopes to book 30 A380 orders this year, but he says that will be “a stretch.”
Next year, the aircraft maker expects to deliver the first A380 to Emirates Airlines with a maximum takeoff weight (MTOW) of 575 metric tons and range boosted to 8,500 nm.
Also becoming available is a version with an MTOW of 490 metric tons, which helps it comply with airport requirements for a Quota Count (QC) 1 noise level on takeoff and QC 0.5 on landing. Emirates is lobbying to operate into slot-constrained London Heathrow Airport in early morning hours, and the lower noise footprint is expected to be part of that push.