Airbus Identifies Heat, Humidity As Causes Of A380 Wing-Spar Cracking

Credit: Ovidiu Dugulan/Alamy

FRANKFURT—A phenomenon called hydrogen assisted cracking or hydrogen embrittlement has been identified as the cause of accelerated crack development in certain wing spars of Airbus A380s that have been stored for extended periods of time.

“The biggest driver is temperature; the second is moisture,” Pierre-Henri Brousse, head of the A380 program, told Aviation Week. When aircraft are on the ground and exposed to extreme weather conditions, hydrogen is diffused into the materials and causes embrittlement of the aluminum alloy, which in turn makes the generation of cracks easier.

  • Inspections to include “factored time on ground” 
  • Storage recommendations will not change for A380 and other aircraft types
  • MRO capacity shortage makes repair work challenging

The findings are behind a May 11 airworthiness directive (AD) issued by the European Union Aviation Safety Agency (EASA) that introduced the concept of “factored time on ground” (FTOG) and required inspections and potentially repairs at intervals also linked to actual aircraft age and a maximum takeoff weight (MTOW) threshold of 510 tons.

The affected areas are the top and bottom flanges of the outer rear spar (ORS) between ribs 33 and 49. Previous ADs also included instructions for other parts in which defects had been found—the outer inner front spar (OIFS) between ribs 8 and 14 and the outer front spar between ribs 38 and 49.

EASA and Airbus had determined as early as 2019 that aircraft have to be inspected 15 years after the date of the wingbox assembly.

Following the findings, the maintenance limit was pulled forward twice. EASA published an AD on Aug. 31, 2022, expanding on a 2019 directive. In the AD, EASA said: “Occurrences have been reported of finding cracks in the affected areas of the wing ORS on in-service A380 aeroplanes. This condition, if not detected and corrected, could reduce the structural integrity of the wing.” The 2019 AD, based on Airbus’ service bulletin A380-57-8263, had initially set the 15-year limit. However, “since that AD was issued, it has been determined that additional areas may be affected by the same unsafe condition, and that all MSN (manufacturer serial numbers) must be inspected.” EASA added in December 2022 that “recent inspection results have indicated the need for ORS inspection from 15 years to 12.5 years.” That was later revised to 11.5 years—with the initial date of wing box assembly as the reference point.

But that remained insufficient. “We inspected some aircraft that were younger than the threshold described by the regulator,” Brousse said. “And we had some findings.”

Airbus then launched a deep dive into the data to try to understand why aircraft as young as 10 years (after wing box assembly and therefore with sometimes significantly fewer years in revenue service) were developing the cracks. “We accumulated a sample that became statistically relevant,” Brousse said. Eventually, the research yielded results—namely that storage conditions have an effect on how fast the cracking develops.

Importantly, the findings will not “substantially change” Airbus’ recommendations for storage of the A380 or any other type. The aluminum alloy of the affected spars is no longer used in any other Airbus aircraft and is changed to a different material when parts are replaced during repairs. “We have no concerns for other components,” Brousse said.

Airbus has not disclosed which airlines are most affected by the defects. However, Emirates said in November 2022 that it is dealing with the issue. The airline had parked many of its A380s at the Dubai World Central airport during the coronavirus pandemic, where they were exposed to particularly high temperatures and humidity during summer. Qatar Airways and Etihad are two more Gulf carriers with A380 fleets, though Etihad is only now beginning to return its A380s to service.

According to Aviation Week Network’s Fleet Discovery database, 135 A380s are in active service, with Emirates operating 87 of them. Singapore Airlines and British Airways are flying 11 of the aircraft each. Qatar Airways and Qantas are following with seven and six, respectively. Most current A380 operators are in the process of returning more of the aircraft from storage, given how fast demand has rebounded on long-haul routes.

Emirates has two more aircraft in parked/reserve status, six are parked and 26 are stored.

According to Airbus, wing inspections take about one week. The non-destructive test inspections can typically be performed by airlines in-house. Affected parts can be repaired through local stopholes or reinforcements, or will be replaced. Stopholes can be introduced in one shift, while the more extensive repairs can take one week per area affected.

Finding enough MRO capacity to deal with the repairs is an ongoing issue, Brousse said. However, he described the situation as manageable and now that A380s are being taken out of service because of the cracking, Airbus is trying to find more MRO providers globally that have the needed A380 capability and free capacity. The manufacturer is also helping with repairs of some aircraft that are performed in Airbus hangars in Toulouse. 

Emirates has returned younger aircraft first to avoid running into inspection intervals early. An Emirates spokesperson said the airline is reviewing the inspection requirements outlined in the May 11 EASA AD. “Currently, we see minimal disruption to our scheduled A380 operations,” the spokesperson told Aviation Week. “We are working on the mid-longer term MRO support requirements for our A380 fleet. We expect a large part of the work will be conducted at Emirates’ Engineering Center, and we are also looking at supplementary support from Airbus and our MRO partners.”

Jens Flottau

Based in Frankfurt, Germany, Jens is executive editor and leads Aviation Week Network’s global team of journalists covering commercial aviation.


1 Comment
I am a little bit puzzled that humid air would be sufficient to cause hydrogen embrittlement and be the cause for propagating cracks through the spar. Although hydrogen embrittlement is a well-known engineering issue, it requires the presence of atomic hydrogen, which I don’t believe was the case with the A380s parked by EMIRATES. Did, however, AIRBUS investigate SCC (Stress Corrosion Cracking)? SCC occurs even at a lower stress level. I experienced it on bolted connections and the solution was to reduce the pre-load of the bolted connections to less than 50% of the max allowable elastic stress. SCC occurs everywhere even in nuclear power plants and here again, the solution is to find the right combination of materials and to reduce the stress level.
Shouldn’t AIRBUS consider modifying the mechanical design of the top and bottom flanges of the outer rear spar in order to reduce the stress level in the areas of concern? I would be ready to bet that the main areas of crack propagation are around bolted or highly stressed riveted connections. Wouldn’t higher gauge bolts or rivets and increasing slightly the thickness locally around the connections fix the problem?
Bernard Guillaume
Woluwe Saint-Pierre Belgium