Fort Worth, Texas American Airlines canceled about 325 flights Wednesday so its crews could inspect some wire bundles aboard its MD-80 aircraft.
The canceled flights represent about 14 percent of the estimated 2,300 flights that the nation's biggest airline had scheduled for the day. The highest concentrations of the cancellations were in the airline's hubs at Dallas-Fort Worth and Chicago O'Hare international airports.
American's entire fleet of MD-80s was being inspected, spokesman Tim Wagner said.
Separately, Delta Air Lines said it was voluntarily reinspecting wiring on 133 MD-88 and MD-90 airplanes. However, it had no estimate Wednesday on how many flights it might need to cancel, a spokeswoman said.
At American, the need for the new inspections became known during an audit of the carrier by a joint team of inspectors from the Federal Aviation Administration and the Fort Worth-based airline.
The inspection involves proper spacing between two bundles of wires in the plane's auxiliary hydraulic system, Wagner said. It must be installed "exactly according to the directive," he said.
Of the 80 planes that the airline decided needed modification, about 20 have returned to flying, Wagner said. He said no flights for today had been canceled as of Wednesday evening.