Screws missing from second Boeing 737 Absence of tail vTC fasteners is not a hazard, FAA says

January 14, 1998|By SEATTLE TIMES

SEATTLE -- Sheet-metal fasteners have been discovered missing on a second Boeing 737 over the weekend during a mandatory inspection of horizontal stabilizers on newer models of the airplane, the government says.

A Continental Airlines 737, assembled in Renton, Wash., and delivered in August, was missing four consecutive screws on the top leading edge of the horizontal stabilizer, the Federal Aviation Administration and the airline said Monday.

A horizontal stabilizer is a small wing at the back of a plane that enables climbs, descents and level flight.

The screws were replaced -- "a five-minute job," said Continental spokesman David Messing in Houston -- and the plane was returned to service.

Meanwhile, the 737 crash in Indonesia that prompted the scrutiny is vexing investigators, who are focusing on a possible structural failure in the plane's tail, according to Aviation Week and Space Technology, but are faced with myriad other possible causes.

The inspection order was prompted by the discovery of missing fasteners in the wreckage of SilkAir Flight MI-185, a 10-month-old 737 that inexplicably crashed on the island of Sumatra Dec. 19 while en route from Jakarta to Singapore at 35,000 feet.

The crash killed 104 people.

The National Transportation Safety Board, the FAA, Boeing and Australian experts, assisting Indonesian and Singaporean authorities, could not find 26 fasteners on the leading edge of the right-side horizontal stabilizer or one of two bolts attaching one of three elevator-hinge brackets.

An elevator is a flap on the rear of the stabilizer that helps control the vertical direction of flight.

There is no reason to believe the missing fasteners caused the crash, the FAA has said, and it is uncertain at what point the screws might have come off the airplane, or if they were ever there.

But Monday's edition of Aviation Week reported that investigators are focusing on the plane's tail section, which was found on land.

The main wreckage was found in the muddy Musi River.

In its 737 inspection order last week, the FAA said the stabilizer "may have separated from the airplane prior to impact."

The Continental twin jet that was missing the screws was one of three 737s on which minor problems were found as a result of inspections ordered last week by the FAA.

In all, 68 U.S.-registered 737s delivered in about the past two years were checked.

An earlier FAA estimate that 95 U.S. planes were subject to inspection was not correct. In all, 211 planes were cited in the directive, but most are of foreign registry.

Last week, another U.S. plane was found to be missing a single fastener on a stabilizer's leading edge, and a third plane had a slightly loose bolt on a hinge bracket that attaches an elevator to the stabilizer. Both were in the Southwest Airlines fleet.

None of the missing fasteners on the three planes posed a safety hazard, said spokesman Tim Pile at the FAA's Transport Airplane Directorate in Renton.

"It would appear on the surface that would not be a trend," Boeing spokeswoman Susan Bradley said.

It is unclear how fasteners on relatively new jets could come loose. It's conceivable they weren't installed in the first place, as the FAA noted in its inspection order. Or the screws might not have been tightened properly during manufacture or maintenance.

Boeing's Bradley said the four missing fasteners on the Continental twin jet were among 231 screws on each side of the airplane that attach the curved-metal leading edge of the horizontal stabilizer to the top of the main structure.

There also are 231 fasteners attaching the leading edge to the bottom side of the stabilizer. The screws are about 2 inches apart.

If the entire leading-edge piece were to come off the stabilizer on one side of a plane, it would be aerodynamically troublesome, but the plane could fly safely, Bradley said.

Pub Date: 1/14/98

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