Alaska Airlines Flight 261
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| Occurrence | |
|---|---|
| Date | January 31 2000 |
| Summary | Mechanical failure |
| Site | Pacific Ocean near Anacapa Island, California |
| Fatalities | 88 |
| Injuries | 0 |
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|- Template:End frame Alaska Airlines Flight 261 was a flight route operated by Alaska Airlines that provided service between Puerto Vallarta, Mexico, San Francisco International Airport, and Seattle-Tacoma International Airport. On January 31, 2000, the flight crashed into the Pacific Ocean off the coast of Los Angeles, killing all on board.
During the initial climb, the crew realized that there were problems with control of the aircraft. They determined that the horizontal stabilizer had jammed. Thus, the aircrew could not trim the aircraft, which involves making fine adjustments to the positions of the flight control surfaces to keep the plane stable in flight. This left the aircraft flyable, but difficult to keep level. In an effort to correct the problem, the pilots attempted to overcome the jam with the primary and alternate trim systems. At first, their efforts had no effect. After discussions with airline mechanics and dispatchers on the ground, the crew decided to divert the flight to Los Angeles International Airport (LAX).
Meanwhile, the crew continued to troubleshoot the problem. Seven minutes after the decision to divert, the crew was successful in moving the stabilizer. However, the stabilizer moved all the way to a full leading edge up position. This unexpected movement had the effect of causing the aircraft to pitch down suddenly, entering a dive.
Only by exerting large forces on the control columns were the pilots able to regain some control of the airplane and continue flying toward LAX. After consulting with a mechanic on the ground, the pilots debated attempting to adjust the stabilizer trim again. They finally decided to leave the stabilizer as it was. Less than a minute after that decision, about ten minutes after the first dive, an "extremely loud noise" was recorded on the cockpit voice recorder and the aircraft entered a second and final dive. The plane inverted and impacted the Pacific Ocean at high speed. All 83 passengers and five crew members died on impact.
The flight crashed about twenty miles (thirty-two kilometers) northwest of Los Angeles International Airport into the water off Point Mugu, California. The last radio contact with the aircraft occurred while the plane was passing 17,000 feet at a low speed of 119 knots.
A report by the National Transportation Safety Board (NTSB) attributed the crash to insufficient lubrication of the jackscrew that moves the horizontal stabilizer up and down on the MD-80. Because the jackscrew was not properly lubricated, it wore much faster than the designers of the plane had expected it to, and eventually siezed. When the pilots tried to free the stabilizer, threads on the jackscrew sheared completely off, and the stabilizer deflected beyond its design limit. Ten minutes later, a second part of the mechanism that was holding the stabilizer in place failed, causing the leading edge of the stabilizer to deflect even further up, sending the aircraft into a dive from which recovery was impossible.
The board also noted that the designers of the aircraft did not provide for a backup system in the event that the jackscrew threads completely failed. Instead, the designers relied on inspections to determine when the jackscrew had worn enough to warrant replacement. The NTSB noted that it is not appropriate to rely solely on maintenance and inspection to identify impending failure of a single-point critical component.
A possible contributing factor in the crash was the method that Alaska Airlines used to check for wear of the jackscrew assembly. The procedure given by the aircraft manufacturer required a special bracket to be installed on the aircraft. In addition to the manufacturer's bracket, Alaska Airlines fabricated brackets in its own maintenance shops. However, the brackets that they made did not match the specifications required of the bracket.
After the crash, the use of flight number 261 was retired and the route is now known as flight 289.
This crash was featured in National Geographic's Air Crash Investigation.