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Monday, September 9, 1991 - Page updated at 12:00 AM

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Boeing Tells 757 Owners To Replace Part -- Faulty Thrust-Reverser Valve Blamed In 767 Accident That Killed 223

Boeing Commercial Airplane Group today advised its 757 customers to replace a flawed valve in thrust-reverser systems of planes powered by Pratt & Whitney engines.

The action came as Thai authorities pinpointed the thrust reverser as the cause of the crash of a Lauda Air 767-300ER in Thailand last spring.

In early August, Boeing alerted airlines worldwide that more than 1,600 late-model 747s, 757s, 737s and 767s had reverser systems common to the one now implicated in the May 26 Lauda tragedy, which killed all 223 on board.

So far, Boeing apparently has not advised airlines to do anything outside of routine maintenance on 747s and 737s. Reverser systems on 82 767s that use Pratt & Whitney PW4000 engines, as the Lauda jet did, continue to be banned from use.

Replacement of the valves on 757s eliminates the chance that a worn O-ring seal could cause the valve to inadvertently deploy a reverser in flight, as Boeing discovered in tests a few weeks ago.

However, authorities are still conducting tests to determine whether a stray electrical signal, vibration or some other phenomena could also cause the valve to deploy a reverser in flight, sources said.

The latest developments focus on the potential hazard to millions of people flying every day on newer Boeing jets that a reverser could deploy during flight, and possibly throw the twin jet into an uncontrollable dive.

Today's service bulletins may be followed as early as tomorrow by orders from the Federal Aviation Administration to replace the valve. In the most serious cases, the FAA generally issues such "airworthiness directives" after bulletins from airplane manufacturers.

Today's confirmation by a Thai official that the thrust reverser caused the Lauda crash is expected to be followed Sept. 18 by a formal announcement from the U.S. National Transportation Safety Board and Thai authorities. They apparently have ruled out sabotage, explosions and fire as causes.

The confirmation comes as the same time as the FAA is preparing orders for thrust-reverser inspections and changes not only to Boeing 757s, the 767's sister ship, but also to hundreds of other jetliners manufactured by Airbus Industrie and McDonnell Douglas. Other Boeing jets likely will be scrutinized, as well, before the thrust-reverser issues are settled.

"New (FAA) orders for these planes will come quickly, maybe as early as this week," David Duff, FAA spokesman in Seattle, said last night. "People will be surprised how comprehensive and broad they will be."

The FAA earlier ordered operators of 767s equipped with Pratt & Whitney 4000 engines to lock their thrust reversers and not use them until they can be redesigned.

The Boeing service bulletins were sent today to customers who bought 174 757s equipped with Pratt & Whitney engines. Steve Smith, Boeing spokesman, said last night that the planes are flown by Northwest, United, Delta Air Lines, American Trans Air (a charter operator) and United Parcel Service in the U.S., and by foreign carriers Royal Air Maroc, Condor, Ethiopian, Shanghai and Ladeco of Chile.

The operators are being asked by Boeing to inspect the wiring to their thrust-reverser systems and to replace valves that use O-rings with ones that have a seamless design. Airlines had the option of using two valves, one with and one without the O-rings, said Bob Kelley-Wickemeyer, chief engineer for technical issues and certification in Boeing's Renton division, where the 757 is produced.

The changes are being ordered as result of bad wiring found in checks of reverser systems in Boeing 767s, required after the Lauda crash.

Kelley-Wickemeyer said no thrust reverser has ever failed on a 757. Thrust reversers help planes brake on the runway by reversing the air flow in the engines.

Models equipped with Rolls-Royce engines are not affected by today's service bulletin, Kelley-Wickemeyer said. General Electric, the other major engine manufacturer, does not supply the 757.

Today's announcement from Bangkok follows new details reported Saturday by one of the FAA's top officials, Anthony Broderick. He told the Washington Post that wind-tunnel and other tests conducted on the 767 showed that the plane became almost impossible to control if a thrust reverser deploys in flight.

Crash investigators found that the left-engine thrust reverser on the Lauda jet had deployed in flight. A complex monitoring system is supposed to notify the pilot and immediately send the engine into idle if such a situation occurs.

Although Boeing and other officials said earlier the pilot should have been able to control the plane, industry sources told The Post that the new tests showed that a plane at the same power settings as the Lauda jet would roll sharply, yaw to the left and pitch down out of control.

Boeing has refused to discuss its findings.

Broderick, associate FAA administrator for regulation and certification in Washington, D.C., stressed that there is no reason not to fly the airplanes, that the latest actions represent "an abundance of caution."

Boeing has teams of about 100 engineers studying the problem, asking "what if" questions that apparently never were considered when the twin-engine 767 and 757 were certified by the FAA about 10 years ago. Some thrust-reverser deployments have occurred in older planes with different engine arrangements, such as the Boeing 727 trijet and Boeing four-engine 747 jumbo jet.

Broderick said all engine thrust reversers on twin-engine jets in the future must be certified as 100 percent fail-safe.

Kelley-Wickemeyer termed the latest actions short-term solutions, agreeing that more work is needed for long-term protection.

-- Material from Reuters was included in this report.

Copyright (c) 1991 Seattle Times Company, All Rights Reserved.

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