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FAA Orders Tests for PW4000 Engines


WASHINGTON - As part of the Federal Aviation Administration's (FAA) efforts to reduce engine-related incidents and improve reliability, the agency today proposed to order tests for PW4000 engines to prevent high-pressure compressor surges.

The proposed Airworthiness Directive (AD) is based on reports of surge events during the critical takeoff and climb phases of flight. A surge is a loss of engine power that results from an imbalance in the flow of air through the engine. Excessive clearances -- too much space -- between the engine blade tip and the outer casing of the engine can cause unstable air flow and a subsequent high-pressure compressor surge and stall. Aircraft engines can restart and recover from a stall.

Work by the industry and FAA over the past seven years has significantly reduced the surge frequency of PW4000 engines. The surge rate has decreased from a 1993 fourth quarter high of about one surge per 8,000 flights to about one surge per 32,000 flights during the first quarter of 1998. The surge rate has since remained steady.

"These tests should significantly reduce the possibility of engine surges on the commercial fleet," said FAA Administrator Jane F. Garvey. "Knowing that pilots are well-trained and that the PW4000 engine will automatically recover is not enough. We want to eliminate the possibility of these engine surges altogether."

There are 546 engines in the U.S. fleet affected by this AD out of a total of 2,200 engines worldwide. The total estimated cost to U.S. industry is $8.7 million. The FAA estimates that 192 engines will require annual on-wing tests with an average cost of $2,000 per test, $384,000 per year. An estimated 60 engines will require annual off-wing tests with an average cost of $12,000 per test, $720,000 per year. The agency also estimates that 19 high-pressure compressor overhauls will be performed at a cost of $400,000 each, $7.6 million. About 11 unscheduled engine removals will cost $5,000 each, $55,000 total.

PW4000 engines are installed on certain models of Boeing 747, Boeing 767, McDonnell Douglas MD-11, and Airbus Industrie A310 aircraft. Operators include Delta Air Lines, Northwest Airlines, Trans World Airlines, United Airlines and World Airways.