Airbus establishes approaches to fix A380 wing components
If there is an upside to the 's wing-component cracking saga, it may be that it should enable to avoid an embarrassing misstep on its next big development program, the .
Airbus has scrutinized the design process for the twin-widebody in light of lessons learned in determining why wing rib feet in the A380 were failing. It has upgraded its finite-element models and removed from the A350 potentially dubious parts, made of a particular aluminum alloy, replacing them with ones made of aluminum lithium that should be less susceptible to cracking.
For the first time, Airbus will also have an aircraft-wide finite-element model run before the static test article is worked on. Those models have been refined to close the gaps seen in the A380 work, drawing in part on the greater processing power that is available now but was not in hand when the A380 wing design work was first undertaken.
However, those long-term advantages are overshadowed by the difficulties encountered in identifying the problem's cause and having to retrofit 120 A380s to fix the problem. The retrofit must be applied to the 74 A380s already delivered as well as to another approximately 46 in the production system now.
Airbus has developed two approaches it believes will permanently deal with the cracking of some rib feet, says Tom Williams, executive vice president for programs. The problem has led to an airworthiness directive from the(EASA) requiring enhanced inspection intervals and fixes where component cracking is found.
One approach addresses the retrofit repair and the other focuses on altering the production process to avert the problem. The fixes should restore the aircraft life to 19,000 flight cycles and bring inspection intervals back to normal, Williams says.
Airbus expects repair expenses to top €260 million ($327 million) this year. “It has cost the company dearly,” acknowledges Airbus CEO Tom Enders, referring to both the finances and reputation of aircraft maker. It also highlights the risk of trying to innovate, because some of the material choices were made with good intentions but without fully understanding the risks involved.
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-constrainedin early morning hours, and the lower noise footprint is expected to be part of that push.