European safety regulators have ordered inspection of 20 Airbus A380s to check for wing rib-foot damage, following the discovery of two different forms of cracks in the structure.
The aircraft affected are early-delivery airframes comprising 10 with Singapore Airlines, seven with Emirates, one with Air France and two Airbus test A380s.
In an airworthiness directive the European Aviation Safety Agency has ordered operators to conduct a detailed visual inspection of "certain" wing rib feet, and to report findings to Airbus.
The inspections are required within four days, if the A380 has already carried out 1,800 flights, and within six weeks if it has performed over 1,300 flights.
Any operator discovering cracks in the rib feet are required to contact Airbus for instructions.
EASA's directive follows the initial discovery of rib-foot cracks in a Qantas A380 - the aircraft involved in the November 2010 engine failure - and the subsequent discovery of a "more significant" and "new form" of rib-foot crack in a different aircraft, said the authority.
While the earlier rib-foot cracks originated from the rib to skin panel attachment holes, EASA said, the new form of crack originates from the forward and aft edges of the L-shaped rib foot's vertical section.
"It has been determined that the [new type of] cracks may develop on other aeroplanes after a period of time in service," the directive states. The inspections are an "interim" measure, it adds, and further mandatory actions "might be considered".
EASA's directive takes effect on 24 January. It has not been classified as an emergency action.