One of Brazil’s most important airlines yanked 11 more Boeing Co. 737s out of service after conducting a search for cracks, creating a situation where one of the U.S. planemaker’s most loyal customers can’t fly 14% of its fleet.

Gol Linhas Aereas Inteligentes SA removed the jets, older models known as Next Generation planes, in a grounding that will affect 3% of its passengers through Dec. 15, the airline said in a statement Wednesday. The U.S. Federal Aviation Administration last week told operators of older 737 NGs to look for cracks in a structure that helps attach the wing to the fuselage.

The grounding piles pressure onto the carrier, which only flies Boeing 737s and is already contending with the absence of the newer 737 Max, which was grounded in March after two deadly crashes. Wednesday’s action now leaves Gol with 18 planes out of commercial service for reasons beyond its control—about one out of every seven planes it flies.

In a separate statement, Boeing said it regretted the impact of the cracks on Gol and other airlines. The Chicago-based planemaker said it’s working to help its customers make repairs.

The FAA has no authority outside the U.S., but its orders are generally heeded by other nations. The regulator took the action last week after reports of cracks in a part called the pickle joint, which helps attach wings to the fuselage of an aircraft. As of late Wednesday, a total of 686 planes had been inspected with 36 showing evidence of cracking, Boeing said.