By John Goglia
No accident – when I was a member of the National Transportation Safety Board - what brought home for me the importance of using the proper tools was the crash of Alaska Airlines’ Flight 261.
Eighty-eight lives were lost on Jan. 31, 2000, in the crash of the MD-83 en route from Puerto Vallarta, Mexico to Seattle, WA, with an intermediate stop scheduled in San Francisco. The primary cause of the accident was determined by the NTSB to be lack of lubrication of the jackscrew controlling the horizontal stabilizer. The excessive wear caused premature failure of the jackscrew threads which led to the separation of the horizontal stabilizer from the aircraft. The aircraft lost pitch control because of that separation and the pilots were unable to control the aircraft, resulting in the crash into the Pacific Ocean, killing all aboard.
While not the primary cause, a major contributing factor in the chain of events leading to the accident was the failure to use the manufacturer’s recommended tool for checking the wear between the jackscrew and the nut. Among the significant findings, the NTSB determined that Alaska Airlines’ maintenance department manufactured its own tool rather than purchase the recommended one. Some speculated that because the manufacturer’s tool was expensive that this may have been a cost-cutting measure by the maintenance department. Regardless of why the recommended tool was not used, it had fatal consequences for those aboard this particular flight.
Investigation of the accident located and retrieved the horizontal stabilizer jackscrew and nut from the depths of the Pacific Ocean where the debris had scattered. Testing by the NTSB found that the threads were totally worn out. This led investigators to question why this amount of wear had not been noticed at the last jackscrew inspection. That review included not only a review of Alaska Airline’s paperwork, but an actual review of the process used by the airline’s maintenance workers.
That review led investigators to the nonstandard tool that was used to measure the thread wear. Testing of the nonstandard tool found that its measurement of thread wear was not consistent and repeatable. This means that when the NTSB used the nonstandard tool to test thread wear of a part, it got different readings every time it tested the same part.
The manufacturer’s recommended tool was also tested by the NTSB in the course of determining the cause of Flight 261’s fatal dive. Perhaps not surprisingly, that tool gave repeated and consistent readings every time. It’s not hard to imagine that if that tool had been used to measure the wear at the last jackscrew inspection, its readings would have shown the excessive thread wear and the jackscrew would likely have been replaced.
For me, who as a mechanic had “made do” to get a job done, this crash was a powerful lesson in the importance of always using the right tool for the job. And while it is management’s job to provide mechanics with the correct tools, it’s every mechanics’ responsibility to insist on getting the right tool – or getting engineering approval to use an alternative.
