By MATTHEW L. WALD
THE NEW YORK TIMES

WASHINGTON -- Federal investigators say they are deeply concerned about an engine breakup that nearly destroyed a Boeing 767 on the ground in Los Angeles this month because the failure may be the third recurrence in six years of a problem they thought they had eliminated.

American Airlines mechanics were testing the engine in the June 2 incident after the crew of an earlier flight had reported it was not performing properly. During the test, an internal disc came apart, slicing open a fuel tank in the left wing; the fuel spilled onto the ground, where it caught fire. One piece of metal was thrown more than half a mile from the plane.

There were no injuries, and under the rules of the National Transportation Safety Board the event might not even qualify as an accident because there was no intention to fly the plane. But experts say that such "uncontained failures," so called because the engine cowling does not hold in the debris, resemble a roulette game.

"There's 360 degrees around, and it's really the luck of the draw which way the pieces come out," said John Goglia, a former member of the board and an aircraft maintenance expert. If the parts fly off in flight and hit the wing, where fuel is stored, or the fuselage, he said, "the results could be pretty devastating."

The first such explosion occurred in July 1989, during a flight of a United Airlines DC-10. That engine was mounted in the tail, and the debris disabled the plane's hydraulic system. The crew brought the aircraft down in a field at the airport in Sioux City, Iowa, maneuvering only by varying the thrust on the two surviving engines; 111 people were killed.

The incident in Los Angeles is similar to one in September 2000 involving another Boeing 767, this one owned by USAir in Philadelphia. In both cases, mechanics were testing the engines by revving them toward full power when they broke up, leading to catastrophic fires.

In addition, an Air New Zealand 767 had an uncontained failure at 11,000 feet on a flight from Auckland, New Zealand, to Brisbane, Australia, in December 2002. That plane landed safely. But as a result, in March 2003, the Federal Aviation Administration ordered inspections of the part involved. The agency believed that would solve the problem.

The engine in all the incidents was a variation of the popular General Electric CF6. Rick Kennedy, a spokesman for General Electric, said that about 3,400 of the engines are in service and that two-thirds of them have been inspected, with no problems found. The engine involved in Los Angeles was not due for inspection, investigators said.

The inspection interval is usually set at half the number of flights at which engineers think a problem will develop. The inspection limit now is 11,000 "cycles," or engine start-ups and shutdowns. Aviation experts said that one likely outcome was that the government would require inspections at shorter intervals.

Kennedy said that the engines involved were built between 1982 and 2001; in 2001, the company switched to a stronger disc, he said. The engines are used on a variety of large airliners.

The FAA is investigating the incident in Los Angeles, said a spokeswoman, Laura Brown.

A spokesman for American, Tim Smith, said that the airline's insurance company had not yet determined whether the plane in Los Angeles had been damaged beyond repair. It suffered damage to both engines and the fuselage, he said.

Of greater concern, though, is how to prevent the problem altogether.

"I view these as warning shots. If we don't pay attention and figure out what went wrong, we're going to repeat it," Goglia said.

Source: seattlepi.com