European safety authorities are set to order airlines to carry out checks on almost a third of the current Airbus A380 fleet after the discovery of wing cracks on the world's largest jetliner, aviation sources said Friday.

The one-off inspections are expected to affect superjumbo aircraft operated by Singapore Airlines , Dubai's Emirates and Air France .

The two-speed recommendation will call for urgent checks within a matter of days on a handful of the most heavily used aircraft, the sources said, asking not to be identified.

These have been subjected to at least 1,800 take-offs and landings, the part of the flight where the airframe endures the most stress.

A second category of around 20 aircraft that have carried out 1,300 to 1,799 flight cycles must be checked within six weeks. A flight cycle is one take-off and landing.

No aircraft will be grounded pending the checks, which involve taking an aircraft out of service for about 24 hours.

European safety agency EASA said it would issue its recommendations later Friday.

Airbus declined to comment ahead of the EASA publication but said Thursday it had found a solution to tiny cracks spotted in two sets of inspections and pledged to put safety first.

The second set of cracks on the double-decker aircraft's UK-made wings came to light Thursday, two weeks after the problem first emerged during $130 million of repairs to a Qantas A380 that suffered an engine blowout in November 2010.

The A380 entered service in December 2007 with Singapore Airlines, followed by Emirates and Australia's Qantas .

Other operators include Air France, Korean Air <003490.KS>,

China Southern <600029.SS> and Germany's Lufthansa .

Airbus has sold 253 of the 525-seat aircraft, currently listed at $390 million each, and 68 are currently in service.

South Korea's Asiana Airlines <020560.KS>, which plans to induct six A380s between 2014 and 2017, said it was not changing that schedule as yet, but it could reconsider depending on the outcome of investigations into the cracks.

Aircraft do not necessarily face inspections in the order they were delivered. Qantas, for example, uses the A380 on long Pacific routes with proportionately fewer take-offs and landings than those used on shorter runs.

Air France placed the giant A380 at first on the short hop between London and Paris in order to perfect cabin operations.

An Air France spokeswoman declined to comment ahead of the publication of EASA's airworthiness directive.

Emirates, the largest A380 customer, declined to comment. Singapore Airlines was not immediately available for comment.

In a separate incident, Air France said an A380 bound for Montreal turned back over the Atlantic and returned to Paris with 448 people on board late Thursday after a video screen overheated. A spokeswoman denied a report of smoke in the cabin.

(Reporting by Tim Hepher, Harry Suhartono; Editing by James Regan)

Germany Australia South Korea Qantas