Boeing Corp. is recommending that carriers look for a loose bolt in the rudder control system of a 737 MAX aircraft after one of its international operators discovered the defect during routine maintenance, Euronews reports.

Another loose bolt was found in an airplane not yet sold. The aircraft corporation specified that the inspection of the mechanism will take no more than two hours per board.

Operation of the 737 MAX was suspended after two disasters. The aircraft maker admitted that in both cases there was a failure of the maneuverability performance improvement system on board the aircraft. The company corrected the system, after which the U.S. and other countries approved the airliner's return to service.