American Airlines and Delta Air Lines canceled hundreds of flights Thursday as they pulled aircraft from service to comply with a government directive for maintenance checks.
American, a unit of AMR , said it canceled 132 flights on Thursday. Delta said the inspections would result in about 275 cancellations through Friday.
The checks are part of a Federal Aviation Administration audit to assess airline compliance with agency directives, most of which require aircraft inspections.
Maintenance lapses by Southwest Airlines in 2006-07 that were revealed recently triggered the audit.
AMR canceled 318 flights -- about 10 percent of its schedule -- on Wednesday as it inspected the wiring on 300 MD-80 aircraft. The inspections were meant to ensure that wiring for an auxiliary hydraulic pump was properly installed and secured.
By Thursday morning AMR said 243 planes had been inspected, modified if needed, and returned to service; 47 were being serviced; and nine planes had yet to be inspected.
The checks, which take several hours, were expected to be completed by Thursday evening.
Delta said it was inspecting 117 MD-88 aircraft, which will mean the cancellation of about 3 percent of its schedule. The carrier said it expects operations to return to normal by Friday.
The House Transportation Committee and the Senate Commerce Committee have scheduled hearings next month on airline maintenance and FAA oversight.
Airline shares were broadly weaker Thursday, with AMR down 18 cents, or 2 percent, at $8.43 on the New York Stock Exchange. Delta shares were down 29 cents, or 3.3 percent, at $8.45 on the NYSE.