Alaska Airlines Flight 261
| Alaska Airlines Flight 261 | |
|---|---|
 Animation of Alaska Airlines Flight 261 |
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| Accident summary | |
| Accident type | Mechanical failure due to incorrect maintenance, material fatigue |
| place | in the Pacific Ocean at Anacapa Island Coordinates: 34 ° 3 ′ 30 ″ N , 119 ° 20 ′ 48 ″ W |
| date | January 31, 2000 |
| Fatalities | 88 |
| Survivors | 0 |
| Injured | 0 |
| Aircraft | |
| Aircraft type | McDonnell Douglas MD-83 |
| operator | Alaska Airlines |
| Mark | N963AS |
| Departure airport | Puerto Vallarta |
| Destination airport | Seattle-Tacoma Airport |
| Passengers | 83 |
| crew | 5 |
| Lists of aviation accidents | |
Alaska Airlines Flight 261 was a flight on a McDonnell Douglas MD-83 from Puerto Vallarta with a stopover in San Francisco to Seattle on January 31, 2000. The plane crashed into the sea off Los Angeles, killing all 88 people on board.
The plane
The aircraft was an MD-83 built in 1992 that had more than 26,200 flight hours behind it before the crash.
Flight sequence
Start and first problems
After taking off from Puerto Vallarta at 1:37 p.m. PST, the aircraft climbed to cruising altitude and headed for San Francisco. Shortly thereafter, however, problems arose: The horizontal stabilizer was immobile, so that the automatic trim system, which moves the horizontal stabilizer slightly up or down and keeps the aircraft stable when cruising, did not work. For this reason, the pilots had to pull hard on the control stick to maintain their altitude. Two hours after take-off, Captain Ted Thompson and his co-pilot William "Bill" Tansky contacted the airline's maintenance center in Seattle and considered landing in Los Angeles . Neither the pilots nor the maintenance center could find the exact cause of the problem. Thinking that the modules that move the horizontal stabilizer were not working, the pilots attempted to free the jammed horizontal stabilizer one at a time using both the main and the alternate trim systems. It didn't work, however.
Meanwhile, the pilots discussed with a flight dispatcher whether the plane should land in San Francisco or Los Angeles. The pilots finally decided on the latter. The NTSB later said the pilots' decision was prudent and wise; however, the Alaska Airlines flight dispatchers tried to persuade the pilots to continue to San Francisco. The voice recorder recorded that those flight dispatchers were concerned about the schedule in case the flight went to LA.
First dive and interception
When the pilots manually freed the tailplane together with both trim systems at 4:09 p.m. PST, the tailplane moved extremely sharply downward and forced the machine into a steep dive . The aircraft lost 2.3 km in altitude in 80 seconds. Both pilots had to pull together with about 63 kg on the control stick in order to intercept the airplane from its dive and to stay at an altitude of about 7500 m.
Alaska Airlines Flight 261 told flight control in Los Angeles that they had problems with the controls and were planning to land at Los Angeles International Airport. Approach control then asked if the pilots wanted to lower the altitude, to which Captain Tompson replied that he wanted to descend to about 3000 m and be sure that he could pilot the jet; he wanted to descend over the bay. The pilots did not want to fly over populated areas, which the NTSB later commented as very wise, and began the descent.
Second dive and crash
At 4:19 p.m., the voice recorder registered four clearly audible beats, followed by an extremely loud noise. The plane went into a dive again. Several nearby planes that saw Alaska Airlines Flight 261 immediately notified approach control. As a result, approach control Los Angeles tried to contact the pilots. Although you can hear the co-pilot on the voice recorder “ Mayday! “Hears calling, no radio contact has been made.
On the voice recorder you can hear that the pilots were trying to intercept the aircraft the entire time. However, the MD-83 could no longer be saved and crashed into the sea after 81 seconds (4.3 km north of Anacapa Island ). During this time the machine had sunk 5.4 km and a rate of descent of 67 m / s had been exceeded. The plane was completely destroyed when it hit the sea surface, and everyone on board was instantly dead.
examination
Recovery of the wreck and analysis
With a sonar , the investigators found 85 percent of all parts, including the stern and the flight data recorder . Both the threaded metal rod for the trim system and the nut through which the thread moves were found. The threaded rod is rotated by a motor. When the threaded rod rotates, the attached nut moves it up or down depending on the direction of rotation. This in turn moves the tailplane. The threaded rod was found wrapped in metal threads that were identified as remnants of the thread of the attached nut. Later analyzes showed that even before the flight 90 percent of the thread of the nut had been worn off due to frequent use and the thread had been completely sheared off in places during the accident flight. As soon as the thread failed, the horizontal stabilizer was loose and was jerked upwards by the aerodynamic forces, which triggered the first dive. The threaded rod attached to the horizontal stabilizer was still held in place by a smaller nut which is used to limit the trim. However, this was not able to cope with the load that was now occurring, so that after some time it also gave way. With that the complete height control was lost, which caused the final dive. Based on the time of the last inspection of the aircraft, the NTSB determined that the threads of the elevator adjustment were more worn than normal. The observed wear was 300 micrometers per 10,000 flight hours, but it would have been around 25 micrometers usual. The NTSB was looking for potential possible causes for this severe wear and tear. A change in the grease of the threaded rod from type 28 to type 33 was considered, in accordance with Boeing's permission . However, the NTSB determined that this could not be the cause. Another reason considered was insufficient lubrication of this assembly. After careful examination of the threaded rod and the nut, it turned out that there was no effective lubrication at all. Therefore the complete lack of lubrication and the resulting heavy wear and tear on this assembly was declared to be the cause of the accident.
Lack of lubrication and axial play check
The investigation continued to find the cause of the lack of lubrication. In an interview with the maintenance mechanic who last serviced the aircraft on Flight 261, the latter said the maintenance took an hour, while McDonnell Douglas said the time required was four hours. The NTSB concluded that the mechanic had insufficiently lubricated the parts. Laboratory tests, however, showed that in the four months between lubrication and the plane crashing, the wear couldn't possibly be as severe. So there must have been other causes.
To wear the thread (mainly in the mother ) monitor was regularly Axialspielprüfung (end play check) performed. So the NTSB looked for the reason why the wear and tear had not been noticed during the last end play check . During the investigation, it was found that Alaska Airlines was using tools it had manufactured itself in the end play check that did not meet the manufacturer's requirements. Tests revealed that these tools could lead to inaccurate measurements. If precise measurements had been available at the last inspection, it would have been possible that these measurements would have shown the extreme wear and tear and the affected parts would have been replaced. On September 27, 1997, during the last scheduled inspection, during which an axial play test was carried out, the measurement showed wear at the limit of the tolerance, whereupon a work order was drawn up for the replacement of the nut. Three days later the work had not yet been carried out and a re-measurement now showed values below the tolerance. The replacement was not carried out.
Extension of the maintenance intervals
Between 1985 and 1996 Alaska Airlines, with the permission of the FAA, increased the time between lubrication of the threaded rod and between end play checks. Since from this point on, any lubrication or end play check that was not carried out would also have been a way of applying sufficient lubrication or detecting extreme wear, the NTSB investigated the justification for this expansion. Alaska Airlines had little money at that time and tried to save costs through less maintenance. The NTSB believed that Alaska Airlines should have checked that the increase in the time between maintenance times was not a threat. However, nothing like this was ever done. Additionally, the NTSB said maintenance and service personnel training at Alaska Airlines had been inadequate for several years.
Conclusions
The NTSB found the following additional contributing factors to the likely cause:
- Alaska Airlines' increased lubrication intervals and FAA permission, increasing the likelihood of extreme wear and tear
- Alaska Airlines' lengthening of the interval between end play checks and the permission of the FAA, which allowed the extreme wear and tear on the mother to lead to the failure of the horizontal stabilizer without the possibility of detecting this
- the lack of a fail-safe mechanism on the MD-80 (the MD-83 is one of several versions of this type of aircraft) to prevent the catastrophic consequences of a complete mother failure.
Aftermath
After the crash of flight 261 Alaska Airlines was in Port Hueneme a monument near the crash site build, similar to the Swissair after the crash of Swissair flight 111 and the Trans World Airlines after the explosion of the aircraft on the TWA Flight 800 had done . This sundial, designed by Bud Bottoms, casts a shadow on the memorial plaque of the victims every January 31st at 4:22 pm local time.
For their in-flight achievements, Ted Thompson and Bill Tansky were awarded a gold medal for their heroism by the International Air Line Pilots Association . To date, this is the only case that pilots have received this medal after their death.
The accident on Alaska Airlines Flight 261 was covered and broadcast in an episode of Mayday - Alarm in the cockpit under the episode name "Cutting Corners".
Similar accidents
Individual evidence
- ↑ Alaska Airlines Flight 261: Searchers Hold Out Hope for Possible Survivors; Crash Takes Heavy Toll on Airlines Employees' Families. CNN International , February 1, 2010, accessed September 15, 2010 .
- ↑ HistoryLink Essay: Alaska Flight 261 to Seattle crashes into the sea on January 31, 2000. HistoryLink. Found May 31, 2009.
- ↑ a b c d e f g h i j k l m n o p q r s t u v w Aircraft Accident Report: Loss of Control and Impact with Pacific Ocean Alaska Airlines Flight 261 McDonnell Douglas MD-83, N963AS About 2.7 Miles North of Anacapa Island, California January 31, 2000. (PDF; 2.37 MB) NTSB , December 30, 2002, archived from the original on May 3, 2014 ; accessed on May 29, 2014 .
- ^ A b c d Aviation Safety Network> Accident investigation> CVR / FDR> Transcripts> Alaska Airlines Flight 261 - 31 JAN 2000
- ↑ NSTB Final, S. 51/52
- ↑ Kyung M. Song: Alaska Airlines copes with 'saddest, most tragic day'. The Seattle Times, February 2, 2000, archived from the original August 17, 2000 ; accessed on December 17, 2009 .
- ↑ Rebekah Denn: Memorials quieter today, but Flight 261 grief still hurts. Seattle Post-Intelligencer , January 31, 2000, accessed September 15, 2010 .
- ↑ Sam Howe Verhovek: One Year After Alaska Airlines Crash, Relatives Visit Ocean Site in Mourning. The New York Times, February 1, 2001, accessed February 25, 2015 .
Web links
- Aircraft accident data and report in the Aviation Safety Network (English)
- Aircraft Accident Report: Loss of Control and Impact with Pacific Ocean Alaska Airlines Flight 261 McDonnell Douglas MD-83, N963AS About 2.7 Miles North of Anacapa Island, California January 31, 2000. (PDF; 2.37 MB) NTSB , December 30 2002, archived from the original on May 3, 2014 ; accessed on May 29, 2014 .