Airbus has completed modification work on fewer than one-quarter of the in-service A380 fleet, fixes that are required to strengthen wing rib-feet and ribs.

Moving all 122 aircraft through the retrofit program will likely take until the end of 2015.

According to Airbus Executive Vice President-Programs Tom Williams, 27 aircraft have received the permanent fix. Work on another 22 aircraft has begun, but those aircraft are operating with airlines that have chosen to go for a step-by-step approach proposed by Airbus. The aircraft can either be taken out of service for eight weeks to complete the modification in one process, or they can be modified in several smaller steps. Williams says he expects a further 11 aircraft to be completed by the end of June.

All 25 A380s delivered last year initially received the old-design wings that were prone to cracking in some areas, but have had the permanent fix done either in Broughton (where the wings are built) or at the final assembly line in Toulouse before being delivered to airlines. Qatar Airways will be the first airline to receive its A380s with newly designed wings later this spring.

There were several causes for the wing-component cracking problem. One was the use of a specific aluminum alloy (7449) and its heat treatment. The alloy saved weight, but it rendered the component more brittle, causing cracking. Another was in the process of attaching the wing skin to the ribs, where excessive loads were placed on components during assembly. The situation was compounded by failing to account properly for temperature-induced material expansion and contraction during operations.

As part of the retrofit, Airbus is replacing ribs using the more conventional Al 7010, which is well-proven in aerospace applications. The retrofit goes beyond the areas where cracks have been found and also includes ribs 48 and 49 at the outer end of the wing. The retrofit includes 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 have also been redesigned to strengthen them, and an inspection manhole in the area where the cracking occurs is reinforced as well. The wings of the Qatar Airways aircraft are the first that have the new components built in right from the start of production. They are now standard on all A380s.

The permanent retrofit procedure has been approved by the European Aviation Safety Agency (EASA) and returns the aircraft to its full expected service life of 19,000 cycles.

A set of checks and, if needed, interim repairs, is currently required after as few as 500 cycles for aircraft that have not received the retrofit yet. That alone is causing serious operational disruptions for the affected airlines.