Twenty of the more than 60 Airbus A380s in service worldwide are affected by the European Aviation Safety Agency’s (EASA) airworthiness directive (AD) to inspect the aircraft for potential cracks of wing rib-feet.

The AD, issued today, requires A380s with 1,800 flight cycles or more to undergo a detailed visual inspection within four days or 14 flight cycles, whichever occurs first. For aircraft with 1,300-1,800 flight cycles, the inspection has to take place within six weeks or 84 flight cycles, according to EASA.

Singapore Airlines (SIA), the first A380 operator, is affected, as is Emirates Airlines, the largest customer for the aircraft. Air France’s first A380 also has to undergo checks.

SIA, which started examining an A380 before even receiving the AD, says it does not expect the inspections to disrupt its day-to-day operations. A carrier spokesman says SIA has 15 A380s in service, which is one or two more than it needs to maintain its current A380 flight schedule, so taking one out of service for inspections will not cause disruptions.

Emirates said Friday it had inspected aircraft and had another one under examination. Like SIA, Emirates does not expect the AD to have an impact on its operations.

The inspection regime involves draining the wing tanks and opening an access panel. Depending on local rules, the process takes a day or more. A repair action, if deemed necessary, would take several days.

At issue is an L-shaped bracket that attaches the wing skin to the ribs. Each wing has about 2,000 L-shaped brackets (30-40 per rib, with 60 ribs per wing), so the failure of one bracket is not seen as a safety issue. EASA says, “This condition, if not detected and corrected, could potentially affect structural integrity of the aeroplane.”

An Airbus wing expert insists that the cracking is not a flight safety issue and that a short-term fix has been identified in cases where cracks are detected. A longer-term fix to prevent the stress cracks from occurring in the future also has been identified.

Where cracks are found, the bracket has to be unbolted and a new one spliced into the section. Whether that is a permanent fix or an interim measure is still being assessed.

As part of the root cause analysis, Airbus instrumented one of its own aircraft to assess whether it had erroneously estimated the loads the wing would bear, leading to the cracks. But the aircraft maker determined that was not the case. Instead, it found that the likely culprit is the assembly process, which places too much stress on 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 for the long-term solution.

EASA notes that this AD “is considered to be an interim action to immediately address this condition.” But, it adds, “further mandatory actions might be considered” as a result of the ongoing investigation.

The 20 A380s identified in the AD as needing inspection are likely to be the only aircraft affected by the AD because Airbus and EADS are working on a long-term strategy for the fleet and none of the other A380s are due to reach 1,300 flight cycles in the next six weeks, says an EASA official.