The US National Transportation Safety Board says an engine fire on an American Airlines Boeing 767-300ER in February would not have occurred had the Federal Aviation Administration issued an airworthiness directive after a similar problem in 2006.

The NTSB in a 12 July letter is recommending that the FAA issue a new airworthiness directive (AD) forcing operators to correct the potential problem.

American flight 837, departing the John F. Kennedy (JFK) international airport for Port au Prince, Haiti, on 8 February with 201 passengers and 12 crew members, experienced a fire in the right engine while climbing through 9,000ft (2,743m). The pilots declared an emergency and returned to the airport for an overweight, but uneventful landing.

Damage to the General Electric (GE) CF6-80C2 engine, including thermal damage to the interior surface of the right thrust reverser cowl and burns on "numerous" wires and cables, was traced to a fire fuelled by jet fuel that had sprayed from a distorted fuel tube flange. Investigators later determined that the leak had been caused by a bracket and a spray shield that were installed in the reverse order.

The same conclusions were drawn from the aborted mission of a Delta Air Lines Boeing 767-300ER that departed Rio de Janeiro for Atlanta in July 2006. In that case, the left GE CF6-80C2 engine experienced a fire at 3,000ft on climb out resulting in a single-engine, overweight landing in Rio.

Ten years before the Rio failure, GE had issued a service bulletin (SB) that introduced a one-piece spray shield and support bracket, in part to eliminate the potential for installing the two individual parts in the wrong order - the root cause of both the American and Delta failures that would follow.

"The SB was initially issued as a category 7 bulletin, meaning that [GE] recommended operators incorporate the SB at their discretion," says the NTSB. "However, following the Delta Air Lines engine fire at Rio de Janeiro, [GE] elevated the bulletin to category 3 in March 2007, meaning that [GE] recommended operators accomplish the SB at the engines' next shop visit."

The American 767 went to the shop two years after the SB was issued, but the change was not made, nor was American required to do so.

"The [NTSB] notes that, unlike an AD that mandates the accomplishment of a particular task, manufacturer SBs are only recommendations to take certain actions. Accordingly, American Airlines was under no obligation to comply with [the SB], even after [GE] elevated the SB to category 3."

American later told the NTSB that its fleet of CF6-80C2-powered 767s "have been operating with a mix of two- and one-piece bracket and spray shields over the past 20 years" and that until the 8 February 2012 engine fire, "there was no economic reason to replace the two-piece bracket and spray shield with the one-piece bracket and spray shield and, thus, the operator had not."

The NTSB says the FAA should have issued an AD requiring operators to replace the two parts with the combined part after the Delta engine fire in 2006, in part since the 767-300ER is approved for extended operations (ETOPS), and as such, would have to operate on a single engine for as long as three hours had an engine fire occurred mid-flight rather than at takeoff.

"The NTSB concludes that, if the FAA had issued an AD to require installation of the one-piece bracket and spray shield on CF6-80C2 engines (as recommended [in the SB]) following the July 2006 Delta Air Lines engine fire at Rio de Janeiro, the engine fire on American Airlines flight 837 would not have occurred," the agency says.

Source: Air Transport Intelligence news