The FAA began looking more closely at airlines' compliance with safety directives in recent weeks, after it was criticized for letting Southwest operate planes that had missed inspections for cracked fuselages.
In the past few weeks, the FAA levied a $10.2 million penalty against Southwest and conducted new inspections at all US airlines, leading to flight cancellations at Southwest, Delta and United.
FAA spokeswoman Diane Spitaliere said inspectors found problems with the wiring bundles at 15 of 19 American MD-80s that it checked this week.
The 2006 safety order from the FAA directs airlines in how to pack and stow wiring to a hydraulic pump in the wheel well to prevent the wires from rubbing together.
According to the FAA, shorted wires could ignite fuel vapors and cause a fuel-tank explosion that could destroy a plane.
The explosion of TWA Flight 800 off New York's Long Island that killed all 230 people aboard in July 1996 was blamed on fuel vapors ignited by wiring. But it was a Boeing 747, not an MD-80, and investigators believe the disaster involved different wiring from the bundles now under scrutiny.
Brian Stirm, an aircraft-maintenance expert at Purdue University, said airlines had plenty of time for the inspections and that even an untrained mechanic could spot a problem.
The cancellations could hardly come at a worse time for American. Its parent, AMR Corp., is scheduled to report first-quarter earnings in two weeks, and analysts are forecasting a loss of more than $300 million. High fuel prices and the downturn in the economy are hurting the industry.
American officials said the company would give $500 travel vouchers to anyone stranded overnight. It also paid for hotel rooms and meals for an undisclosed number of passengers.
Bob McAdoo, an airline analyst, said passengers might soon forget the debacle, especially since several other major airlines have canceled flights recently. But he said passengers who missed big events like weddings might avoid American again.
Kathy Neer of Santa Fe, N.M., was caught up in both waves of cancellations to and from a vacation in Paris. She and her husband were stranded in Dallas on Tuesday on the final leg of their journey home. American gave the Neers a voucher for a hotel room and seats on another flight home Wednesday.
"They say our flight is leaving at 3:55 pm, but do you think we trust them?" Neer said. "After being burned twice, we're a little skeptical."