American Airlines said it was canceling up to 500 flights Tuesday, perhaps 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.

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.

The Fort Worth-based airline, a unit of AMR Corp., is doing the work in Chicago, Dallas and a handful of other locations. The airline said it would put displaced travelers on other American flights or those operated by competitors.

American operates about 2,300 daily flights.