Pins Blamed For 737 Accident -- Safety Board To Call For Engine- Mount Replacement

DALLAS - Faulty engine mounts on 737-200 jetliners - a problem authorities thought they had resolved four years ago - are being blamed for an engine falling off another aircraft.

The National Transportation Safety Board is expected to ask that all airlines replace the engine mounts on Boeing 737-200s, in the wake of a Jan. 7 accident at Dallas-Fort Worth International Airport.

Boeing spokesman Steve Smith said the company would have no comment "until we see something in writing."

Although the NTSB does not consider the current hardware unsafe, it found in investigating the Dallas-Fort Worth incident that "there's ways to make it better," said NTSB investigator Hector Casanova.

Given the thousands of flights that 737s make nationwide each year, four incidents in a five- or six-year period hardly pose a hazard, he said.

Casanova said the NTSB will probably recommend that some of the hardware be changed and that the bolts used in conjunction with it be enlarged.

A Delta Air Lines 737-200 twinjet had climbed to about 200 feet after takeoff when breakaway safety bolts, called cone pins, that secure the right engine to the wing sheared under stress, Casanova said. The engine bounced into the grass on the right side of the runway, and the airplane returned safely.

Engine mounts on Boeing jetliners are a major safety issue. In 1988, the Federal Aviation Administration ordered cone pin engine mounts inspected and beefed up on all 737-100s and 737-200s after a series of accidents in which engines fell off 737s. Boeing 727 tri-jets also use the cone pin system.

Other Boeing models - 747s, 767s, 757s, 737-300s, 737-400s and 737-500s - use different types of breakaway bolts, called fuse pins, which are suspected of contributing to two fatal 747 crashes in the past year.

Casanova said the right engine mount on the Delta jet failed even though it had a secondary support structure ordered by the FAA in 1988.

Before that, a safety cable was supposed to hold the engine on in emergencies, Casanova said.

"Then we came up with this secondary support structure, which was supposed to be the cat's meow," he said. "But in this case, the hardware that was supposed to hold the secondary support structure also broke."

Not only did a main mounting bolt fail, but so did the bolts holding the secondary support structure to the wing.

The improvement was triggered by a December 1987 incident in which an engine separated from a USAir 737 shortly after the flight departed from the Philadelphia airport. Inspectors found cracks caused by metal fatigue in one of the three bolts holding the engine in place.

A subsequent report by the NTSB showed that once the rear bolt separated, the two forward bolts and a support cable broke because of added stress.

The board said that a similar bolt failed on a Southwest Airlines Boeing 737 on Jan. 3, 1986, after it took off from Dallas' Love Field airport, but that the two forward bolts kept the engine from falling off. The plane returned safely.

Then on Jan. 20, 1989, the right engine fell off a Piedmont Airlines 737-200 as it took off from Chicago. The aircraft did not yet have the secondary support installed.

Boeing will manufacture kits for replacing the engine mounting hardware, if the FAA orders the changes recommended by the NTSB. Boeing's Smith said he could not comment on how much the improvements would cost.