In a statement, Qatar Airways said it had been monitoring the degradation under the paint on the aircraft’s fuselage for some time. It described the issue as “a significant condition” without elaborating.

“Following the explicit written instruction of its regulator, 13 aircraft have now been grounded, effectively removing them from service until such time as the root cause can be established and a satisfactory solution made available to permanently correct the underlying condition,” the airline said in its statement.

Qatar Airways has a fleet of 53 Airbus A350s in both its 1000 and 900 series. The airline has another on order with the Toulouse based aircraft manufacturer. It has ordered a total of 76 aircraft – the largest order of any airline in the world.

In June, Qatar Airways said it would not take any more A350s until the issue was resolved. Airbus declined to comment specifically on the grounding of Qatar Airways. “As a leading aircraft manufacturer, we always communicate / work with our customers,” the statement said. “We keep those conversations confidential. We have no further comment on our customer operations.”

Currently, Singapore Airlines is the world’s largest operator of the A350, of which 56 are now in its fleet. The airline did not respond to a request for comment. In the United States, Delta Airlines has 15 fleets. The Atlanta-based carrier did not immediately respond to a request for comment.

The A350 has a list price of $366.5 million, although buyers often get discounts on bulk deals. Akbar Al Baker, CEO of Qatar Airways, is known for his tough, confrontational approach to conversations with manufacturers and others.