American Airlines, a unit of AMR,Tuesday again grounded planes and canceled hundreds of flights to conduct additional safety inspections of its MD-80 aircraft, the airline said.
American said in a statement that the Federal Aviation Administration (FAA) raised new concerns about recent wiring inspections on the mainly older narrowbody planes that resulted in canceled flights two weeks ago.
The current and previous inspections stem from an industrywide FAA review of airline compliance with agency safety directives.
Several carriers have grounded aircraft as a result of the audit, which was triggered by inspection and maintenance lapses at Southwest Airlines and pressure from government watchdogs and congressional investigators to take action.
American said it had canceled up to 500 flights Tuesday, more than 20 percent of its daily mainline service, and additional cancellations were likely Wednesday.
"We've been working in good faith to ensure that we are in compliance with this airworthiness directive," said Gerard Arpey, AMR's chairman and chief executive.
Arpey apologized to customers for "once again" inconveniencing them.
American operates nearly 300 MD-80 aircraft, about half its overall fleet, mainly on busy routes servicing its Dallas and Chicago hubs.
The case at American relates to a 2006 FAA order to ensure that wiring in MD-80 wheel wells is properly installed and secured.
The FAA said it rechecked a sampling of American's planes in selected locations that were inspected in March as part of the safety audit and found the work on some still did not meet requirements of the original order.
"We will be looking closely over the next several days. We will be checking to make sure that the work has been done correctly," said FAA spokeswoman Alison Duquette.
Any plane that does not conform to detailed technical specifications of the order will not be returned to service until the work is completed, American said.
American reaccommodated passengers on other American flights or those operated by other airlines.
Delta Air Lines , which also canceled flights two weeks ago to recheck wiring on its MD-series fleet, said late Tuesday it was working with the FAA to ensure "continued compliance." No additional action is planned "at this time" nor are there any flight cancellations, Delta said.
The U.S. Senate is planning a hearing on inspection and maintenance lapses on Thursday.
The House Transportation Committee, which exposed missed inspections for fuselage cracks at Southwest, heard testimony last week from whistle-blowers and government watchdogs alleging years of lapsed inspections and weak FAA oversight at that carrier.
American has not detailed the financial impact of the service disruption in March. AMR shares gained 16 cents, or 1.6 percent, to $10.32 in regular trade on the New York Stock Exchange but lost 12 cents after hours.