Sources say that the FAA could hit American with a fine similar to the record $10.2 million penalty assessed in 2008 to Southwest Airlines. Southwest, which was accused of making 60,000 flights on planes that had missed inspection for structure damage, ended up paying a $7.5 million penalty in a settlement with the FAA in March 2009.

An FAA spokesman told the AP that the American Airlines investigation was not finished and that it was too early to speculate on how much the airline might be fined.

The probe into American was launched in 2008 after safety concerns were raised about almost 300 of the company's MD-80 aircraft. Improper bundling of wires in the wheel well of the MD-80 posed a fire hazard.

While the problem in the wheel wells has been fixed, the investigation uncovered other possible irregularities and violations with American's maintenance operations.