Washington (CNN) -- The federal government is ordering airlines to perform more frequent inspections on certain Boeing 767 aircraft after cracks were found on engine pylons on two planes, saying undetected cracks could lead to engines separating from the wings.
The Federal Aviation Administration first ordered repetitive inspections of the pylons, which connect engines to the wings, in 2005, specifying inspections at intervals between 1,500 flights and 16,000 flights.
But since that order, the agency says, cracks were found on two planes, one of which had flown only 408 flights since its last inspection, and another that had flown 830 times.
Under the new order, operators must inspect planes every 400 flights, or replace the fittings.
Some 138 planes are affected in the United States, out of 314 planes worldwide. Major U.S. operators are American Airlines, Continental, Delta, FedEx, United, UPS, US Airways and ABX, the aviation agency said.
The agency said the new order applies only to B-767s having the original pylon design. Boeing has improved the pylon in newer planes, it said.