WASHINGTON – Shabby maintenance performed on American Airlines' planes posed a safety risk to passengers and, left unfixed, could have eventually caused an accident.

That's the view of federal regulators, who blamed American for failing to correct how electrical wires on its McDonnell Douglas MD-80 fleet were secured against damage.

American didn't concur – just one of the disagreements that American and the government still have a month after the carrier canceled 3,300 flights in one week.

In its most complete accounting of the cancellations, American said the FAA sent mixed signals about the way to handle the work required by a federal airworthiness directive.

The FAA initially accepted the carrier's work plan before "events unfolded rapidly and unpredictably," the airline wrote in a letter to Transportation Secretary Mary Peters.

Regulators twice threatened to ground the fleet before American did so itself on April 8, according to the airline.

"American Airlines clearly now understands the FAA has made a fundamental shift in the manner in which it's conducted inspections for the past 25 years," said Tim Wagner, an airline spokesman.

The FAA says the rules haven't changed. In its own report to Ms. Peters, it said American had several chances to inspect and repair the wire bundles before the planes were grounded.

The Transportation Department released the reports Friday while announcing other measures to target congestion and improve disclosure of airline delays.

"We want to avoid a situation where a month later, there is still significant disagreement about virtually every fact, virtually every element of what happened," said Brian Turmail, a spokesman for Ms. Peters.

In her own response, Ms. Peters directed the FAA and airlines to improve their communications "when safety inspection disputes are raised."

Although Ms. Peters wrote that she didn't want to assign blame, American could face a civil penalty for the period during which it didn't comply with the directive.

The FAA assessed a $10.2 million penalty against Southwest Airlines in February for flying planes that should have been grounded for inspections required by an airworthiness directive.

Because American owns so many MD-80s, it was involved in writing a 2005 Boeing service bulletin that preceded the issuance of the FAA directive. The FAA noted that compliance with its order wasn't required until March 5, suggesting that American had plenty of time to resolve questions about how work should be done.

On Friday, the FAA released a series of photographs that documented what it called "serious and unacceptable failures" found in late March, during an audit of American and other U.S. carriers. American responded to the audit by canceling 457 flights to make fixes.

That audit was a response to Southwest's highly publicized lapses, which prompted a congressional hearing featuring some of the FAA inspectors who criticized their agency's loose oversight of Southwest.

In its report, American's executive vice president for operations, Robert Reding, suggested the audit was cosmetic.

"We were told repeatedly, 'This audit has nothing to do with safety of flight issues; this is about compliance,' " he wrote.

But similar problems were found in early April when FAA inspectors returned to American's maintenance bases.

"At this point, American had failed to demonstrate its ability to comply with the AD [airworthiness directive] on several occasions," the FAA wrote.

FAA officials declined on Friday to say whether American might face a civil penalty for the way it handled the work.

"We believe then and we believe today we've always been in compliance with that AD," said Mr. Wagner, the airline spokesman.

Separately, American said it's talking to the FAA about its procedures for checking planes for lightning-strike damage. The agency sent a letter to the airline last fall after a mechanic reported concerns about the carrier's revised inspection procedures.

"We think that the way some of the guidance is written could be confusing," said Laura Brown, an FAA spokeswoman.

FAA officials said the inquiry isn't as serious as an enforcement investigation, which could lead to a fine.

Lightning can hit airplanes, sometimes as much as several times a year, but "the airplanes are designed to discharge that electricity and to keep planes flying," Mr. Wagner said.