American Airlines said it was canceling up to 500 flights Tuesday, potentially more than one-fifth of its schedule, to check the bundling of wires in some planes, the same issue that caused the airline to scrap more than 400 flights last month.

American, the nation's largest carrier, said the cancellations could spill into Wednesday and beyond.

The airline said the Federal Aviation Administration raised more concerns about the recent inspections of the wiring in its approximately 300 MD-80 aircraft.

The inspections will focus on issues including the spacing and direction of cords used to secure bundles of wires in the planes' auxiliary hydraulic systems. The company said they were not safety-of-flight issues.

Tim Wagner, a spokesman for the airline, said an FAA inspector checked several planes Monday and found that some of the work performed last month didn't meet the agency's standards.

American operates about 2,300 daily flights. Wagner said 185 flights had already been canceled by late afternoon at Dallas-Fort Worth International Airport, where American often uses MD-80s.

The FAA has tightened inspections of planes at all U.S. carriers since the agency came under fire for letting Southwest Airlines Co. fly planes that had missed safety inspections. American and Delta Air Lines Inc. both canceled flights in late March to perform wiring-related inspections and repairs.

Wagner said the latest grounding of flights was due to "very detailed and technical compliance" with instructions that American gave its mechanics last month for how to comply with the FAA order on wiring in MD-80s, and the work done by the mechanics.

Wagner said the company started pulling planes out of service in mid-afternoon. The work may last just 10 to 20 minutes per plane but could take longer if wiring needs to be rebundled, he said.

It is "quite possible" that the work - and flight cancellations - could stretch beyond Wednesday, he said.

In a statement issued by the airline, Chief Executive Gerard Arpey said, "We regret and apologize that we are once again causing inconvenience to our customers." He said the company was working in good faith to comply completely with the FAA wiring order.

The Fort Worth-based airline said it would put displaced travelers on other American flights or those operated by competitors.

The cancelations and resulting loss of revenue could hardly come at a worse time for American, which is facing high fuel prices and a weakening economy that could hurt demand for travel.

American's parent, AMR Corp., is scheduled to report first-quarter earnings in two weeks, and analysts are forecasting a loss of more than $300 million, according to a survey by Thomson Financial.

Jamie Baker, an analyst with JPMorgan, said in a recent note to clients that he expects airline revenue to decline significantly beginning in the April-June second quarter due to the one-two punch of costly fuel and a possible recession.