American Airlines engine fire due to unapproved maintenance practices

Safety investigators traced a 2007 American Airlines engine fire to unapproved maintenance practices that eluded the carrier's quality-assurance auditors, the National Transportation Safety Board disclosed now.

The September fire happened shortly after American Airlines Flight 1400 departed Lambert-St. Louis International Airport. The pilots returned to the airport without injuries or fatalities to any of the plane's crew or 138 passengers.

Yet the pilots also prolonged the fire by failing to follow a checklist that leads them through steps during such an emergency, the safety board said. Accident investigators said the crew became distracted and failed to quickly shut off fuel to the damaged engine, causing a loss of hydraulic pressure. That led to problems deploying the front landing gear.

"It was a series of people taking shortcuts that accumulated on this particular day into what could have been a much more catastrophic incident," said board member Kitty Higgins.

American has been under closer regulatory scrutiny since last year, when it grounded hundreds of McDonnell Douglas MD-80 jets following federal safety audits. The Federal Aviation Administration last month started a three-month audit of American's safety procedures.

Safety board members said their review was limited to the engine fire, which occurred on an MD-82.

"There was a host of serious problems that ... when you added them all together could have been extremely catastrophic to the point where life could have been lost," acting board Chairman Mark V. Rosenker said.

During the week before the accident, the jet's left engine failed to start on multiple occasions, the board said. Mechanics repeatedly used an unapproved tool, such as a screwdriver, to open a valve that manually starts the engine, the board found. Boeing warned carriers in 1997 that using the wrong tool could deform a pin on the start valve. The damaged pin triggered a malfunction that sent sparks into the metal cover that contains the engine, where there was probably some kind of fuel leak, the board said.

The safety board determined that American mechanics replaced the start valve six times but missed the cause of the failed engine starts: a worn-out, stainless steel air filter. American's audit team also failed to identify the cause of the problem, the NTSB said.

"Where they have found deficiencies in how our personnel performed, we are going to strengthen our training," said Tim Wagner, an American spokesman.

American has started to replace components of the start valve on all MD-80s and plans to complete the work in 2010, Wagner said. The carrier has also increased staffing on its audit team to monitor more mechanical work.