Alaska Airlines Flight 261
Date: January 31, 2000
Aircraft Type: McDonnell Douglas MD-83
Location: Pacific Ocean near Anacapa Island, California
Alaska Airlines Flight 261, was scheduled to fly between Lic. Gustavo Díaz Ordaz International Airport (PVR), Puerto Vallarta, Mexico, to Seattle-Tacoma International Airport (SEA), with an intermediate stop planned at San Francisco International Airport (SFO) when it crashed into the Pacific Ocean about 2.7 miles north of Anacapa Island, California, killing all onboard.
Findings from NTSB determined that the probable cause of the crash was as a result of a loss of airplane pitch control resulting from the in-flight failure of the horizontal stabilizer trim system jackscrew assembly’s acme nut threads1.
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|(Video embedded from YouTube on 27 August 2011)|
There was a fundamental flaw in the design of the MD-83 aircraft as there was an absence of a fail-safe mechanism to prevent the catastrophic effects of total acme nut thread loss.
Hence, in this incident, the single point of failure in the excessive wear of the acme nut threads on the airplane's horizontal stabilizer jackscrew assembly resulted in the loss of pitch control and because the jackscrew assembly is an integral and essential part of the horizontal stabilizer trim system, a critical flight system, degradation this assembly contributed to the crash.
In this case, the fundamental flaw in design was exacerbated by the failure to adhere to the proper systemic maintenance and inspection process of the parts of the jackscrew assembly.
Dirty Dozen Contributory Factors
In the aviation maintenance industry, there is immense pressure to rectify, maintain and deliver aircraft in a timely manner to ensure scheduled departure times are met.
In this incident, pressure to make a scheduled return to service date resulted in records to be falsified to ensure that the aircraft passed the inspection. This was evident as initial measurements of the jackscrew showed that it had was on the brink of wearing out and that a new jackscrew needed to be ordered; but because this would delay the departure of the aircraft, the next log in maintenance records found the plane to be airworthy.
Pressure to allow the plane to be able to fly had resulted in deviation in records and allowed the jackscrew assembly to be on the aircraft for a longer amount of time than it should have instead of being replaced and contributed to the crash2.
Pressure from the company in times of financial crisis in economic downturn also results in cutting of costs with the aim of keeping the plane longer in the air to fly more intensively instead of having it longer in maintenance.
In this incident, the company, to save lubrication costs extended the lubrication interval and as a result contributed in excessive wear of the acme nut threads to failure due to inadequate lubrication. The video also mentions that 6/34 of the fleet of jackscrew assembly after facing new inspections in the aftermath of the crash.
- Lack of assertiveness
Maintenance personnel conversant with the types of maintenance needed for the aircraft in terms of lubrication to prevent excessive wear rate did not speak up despite knowing what could possibly happen if proper lubrication and maintenance checks were not done.
This showed a lack of assertiveness as they were probably more worried about safeguarding their job and hence compromised the safety standards they were thought.
- Lack of teamwork
In times of difficulty, teamwork is quintissential. However in this incident, the video clearly depicts maintenance personnel was rather nonchalent in helping out the pilots when they were facing extreme difficulty in controlling the aircraft when they were facing problems troubleshooting and dealing with the horizontal stabilizer problem.
The maintenance personnel did not see the grave situation the pilots and aircraft were in and as such did not go out of his way to help find a possible solution to the problem by checking with other maintenance personnel or even pilots.
Want to know more?
- AviationKnowledge - The Dirty Dozen (human factors issues) in aviation maintenance
- This article provides a comprehensive feature on the Dirty Dozen human factors in aviation maintenance.