Alaska Airlines Flight 261
Encyclopedia
Alaska Airlines
Flight 261, a McDonnell Douglas MD-83 aircraft, experienced a fatal accident on January 31, 2000 at the Pacific Ocean
about 2.7 miles (4.3 km) north of Anacapa Island
, California
. The two pilots, three cabin crewmembers, and 83 passengers on board were killed and the aircraft was destroyed. It was the highest ever death toll of any aviation accident involving a McDonnell Douglas MD-83. Alaska 261 was a scheduled international passenger flight from Lic. Gustavo Díaz Ordaz International Airport
in Puerto Vallarta
, Mexico, to Seattle-Tacoma International Airport
in Seattle, Washington
, with an intermediate stop planned at San Francisco International Airport
in San Francisco, California
.
The subsequent investigation by the National Transportation Safety Board determined that inadequate maintenance led to excessive wear and catastrophic failure of a critical flight control system during flight. The probable cause was stated to be "a loss of airplane pitch control resulting from the in-flight failure of the horizontal stabilizer
trim system jackscrew
assembly's acme
nut
threads. The thread failure was caused by excessive wear resulting from Alaska Airlines
's insufficient lubrication of the jackscrew assembly."
Of the occupants, at least 35, including 12 employees, were connected to Alaska Airlines or Horizon Air
in some manner, leading many airline employees to mourn for the losses in the crash. Alaska Airlines stated that, during slower traveling days, it was common for employees to fill seats that would have otherwise been empty. Bouquets of flowers started arriving at the company's headquarters in SeaTac, Washington
the day after the crash occurred.
310 (31,000 ft). Approximately 2 hours into the flight, the flight crew, consisting of captain Ted Thompson, 53 and first officer William "Bill" Tansky, 57, first contacted the airline's dispatch and maintenance control facilities in SeaTac, Washington
, and on a shared company radio with operations and maintenance facilities at Los Angeles International Airport
(LAX) discussed a jammed horizontal stabilizer and a possible diversion to LAX. The jammed stabilizer prevented operation of the trim system, which normally would make slight adjustments to the flight control surfaces to keep the plane stable in flight. At their cruising altitude and speed the position of the jammed stabilizer required the pilots to pull on their controls
with approximately 10 pounds (44N) of force to keep level. Neither the flight crew, nor company maintenance, were able to determine the cause of the jam. Repeated attempts to overcome the jam with the primary and alternate trim systems were unsuccessful
During this time the flight crew had several discussions with the company dispatcher about whether to divert to Los Angeles, or continue on as planned to San Francisco. Ultimately the pilots chose to divert. Later the NTSB found that while "the flight crew's decision to divert the flight to Los Angeles...was prudent and appropriate", nonetheless "Alaska Airlines dispatch personnel appear to have attempted to influence the flight crew to continue to San Francisco...instead of diverting to Los Angeles." Cockpit Voice Recorder
(CVR) transcripts indicate that the dispatcher was concerned about the effect on the schedule ("flow") should the flight divert.
Alaska 261 informed air traffic control
(ATC) of their control problems. After the flight crew stated their intention to land at LAX, ATC enquired if they wanted to proceed to a lower altitude in preparation for approach. The captain replied: "I need to get down to about ten, change my configuration, make sure I can control the jet and I'd like to do that out here over the bay if I may." Later, during the public hearings into the accident, the request by the pilot not to overfly populated areas was specifically commended by NTSB board members. During this time the flight crew considered, and rejected, any further attempts to correct the runaway trim. They proceeded to descend to a lower altitude and started to configure the aircraft for landing at LAX.
airliner reported "He's, uh, definitely out of control" Although the CVR captured the co-pilot saying "Mayday
", no radio communications were received from the flight crew during the final event.
The CVR transcript reveals the pilots' continuous attempts for the duration of the dive to regain control of the aircraft. At one point, unable to raise the nose, they attempted to fly the aircraft "upside-down". However the aircraft was beyond recovery; it descended inverted and nose-down about 18,000 feet in 81 seconds, a descent rate exceeding 13,300 feet per minute, before hitting the ocean at high speed. At this time, pilots from aircraft flying in the same area reported in, with one SkyWest Airlines
pilot saying, "and he's just hit the water," meaning the plane had crashed into the ocean. Another reported, "Yeah sir, he, uh, he, uh, hit the water, he's, uh, down." Everyone on board died when the plane struck the water, and the aircraft was destroyed upon impact.
Using side-scan sonar
, remotely operated vehicle
s, and a commercial fishing trawler, workers recovered about 85% of the fuselage (including the tail section) and a majority of the wings. In addition, both engines, as well as the Flight Data Recorder
(FDR) and CVR were retrieved. All wreckage was unloaded at Port Hueneme, California for examination and documentation. Both the horizontal stabilizer trim system jackscrew (also referred to as "acme screw"), and the corresponding acme nut, which the jackscrew turns through, were retrieved. As the jackscrew rotates it moves up or down through the (fixed) acme nut. This up and down motion moves the horizontal stabilizer for the trim system. The jackscrew was found with metallic filaments wrapped around it; these were later determined to be remnants of the threads from the acme nut.
Later analysis estimated that 90% of the threads in the acme nut had been previously worn away, and that they were then completely sheared off during the accident flight. Once the threads failed, the horizontal stabilizer assembly was then subject to aerodynamic forces that it could not withstand, and ultimately failed. Based on the time since the last inspection of the jackscrew assembly, the NTSB determined that the wear had occurred at a much faster than average rate (0.012 inch per 1,000 flight hours, when the expected wear was 0.001 inch per 1,000 flight hours). The NTSB considered a number of potential reasons for this excessive wear, including the substitution by Alaska Airlines (with the approval of the aircraft manufacturer Boeing
) of Aeroshell 33 grease instead of the previously approved lubricant, Mobilgrease 28. The use of Aeroshell 33 was found not to be a factor in this accident. Insufficient lubrication of the components was also considered as a reason for the wear. Examination of the jackscrew and acme nut revealed that no effective lubrication was present on these components at the time of the accident. Ultimately, the lack of lubrication and resultant excessive wear of the acme nut threads were determined to be the direct causes of the accident.
NTSB Animation: Longitudinal Trim System Description and Failure Sequence (.wmv file)
In order to monitor wear on the jackscrew assembly a periodic maintenance inspection called an "end play check" was used. The NTSB examined why the last end play check on the accident aircraft in September 1997 did not uncover excessive wear. The investigation found that Alaska Airlines had fabricated tools to be used in the end play check that did not meet the manufacturer's requirements. Testing revealed that the non-standard tools ("restraining fixtures") used by Alaska Airlines could result in inaccurate measurements, and that it was possible that if accurate measurements had been obtained at the time of the last inspection, these measurements would have indicated the excessive wear and the need for the replacement of the affected components.
(FAA). Since each lubrication or end play check subsequently not conducted had represented an opportunity to adequately lubricate the jackscrew or detect excessive wear, the NTSB examined the justification of these extensions. In the case of extended lubrication intervals, the investigation was not able to determine what information, if any, was presented by Alaska Airlines to the FAA prior to 1996. Testimony from an FAA inspector regarding an extension granted in 1996 was that Alaska Airlines submitted documentation from Boeing as justification for their extension.
End play checks were conducted during a periodic comprehensive airframe overhaul process called a "C-check". Testimony from the director of reliability and maintenance programs of Alaska Airlines was that a data analysis package based on the maintenance history of five sample aircraft was submitted to the FAA to justify the extended period between C-checks. Individual maintenance tasks (such as the end play check) were not separately considered in this extension. The NTSB found that "Alaska Airlines' end play check interval extension should have been, but was not, supported by adequate technical data to demonstrate that the extension would not present a potential hazard."
Systematic problems were identified by the investigation in the FAA's oversight of maintenance programs, including inadequate staffing, its approval process of maintenance interval extensions, and the aircraft certification requirements.
" provisions were needed.
In order for this design component to be approved ("certified") by the FAA without any fail-safe provision, a failure had to be considered "extremely improbable". This was defined as "having a probability on the order of 1 x 10-9 or less each flight hour." However the accident showed that certain wear mechanisms could affect both sets of threads, and that the wear might not be detected. The NTSB determined that the design of "the horizontal stabilizer jackscrew assembly did not account for the loss of the acme nut threads as a catastrophic single-point failure mode."
During the course of the investigation, and later in its final report, the NTSB issued a total of 24 safety recommendations, covering maintenance, regulatory oversight, and aircraft design issues. More than half of these were directly related to jackscrew lubrication and end play measurement. Also included was a recommendation that pilots were to be instructed that in the event of a flight control system malfunction they should not attempt corrective procedures beyond those specified in the checklist procedures, and in particular in the event of a horizontal stabilizer trim control system malfunction the primary and alternate trim motors should not be activated, and if unable to correct the problem through the checklists they should land at the nearest suitable airport.
In NTSB board member John J. Goglia's statement for the final report, which was concurred with by all three other board members, he wrote:
management said that it hoped to handle the aftermath in a manner similar to that done by Swissair
after the Swissair Flight 111
accident, as opposed to the manner that TWA
handled the aftermath of TWA Flight 800
; in other words, to provide timely information and compassion to the families of victims.
The families of the victims approved the construction of a memorial sundial
that was placed at Port Hueneme. The sundial was designed by Santa Barbara artist Bud Bottoms to cast a shadow on a memorial plaque at 4:22 p.m. each January 31.
For their actions during the emergency, Captain Ted Thompson and First Officer Bill Tansky were awarded the Airline Pilots Association Gold Medal for Heroism, the only time the award has been given posthumously.
Both Boeing and Alaska Airlines eventually conceded liability for the crash, and all but one of the lawsuits brought by surviving family members were settled out-of-court before going to trial. Candy Hatcher of the Seattle Post-Intelligencer
said "Many lost faith in Alaska Airlines, a homegrown company that had taken pride in its safety record and billed itself as a family airline."
Two victims from Alaska 261 were falsely named in paternity suits as the fathers of children in Guatemala in an attempt to gain insurance and settlement money. DNA testing revealed these claims to be false.
This crash was featured in a 2004 episode of Discovery Channel (Canada)
's Mayday
television program (also known as Air Crash Investigation and also known as Air Emergency), titled Cutting Corners or Fatal Error.
The Ted Thompson/Bill Tansky Scholarship Fund was named after the two cockpit flight crew members.
Many residents of the City of Seattle had been affected by the disaster. As part of a memorial vigil in the year 2000, a column of light was beamed from the top of the Space Needle
. Students and faculty at the John Hay Elementary School in Queen Anne, Seattle held a memorial for four Hay students who died in the crash. In April, 2001, John Hay Elementary dedicated the "John Hay Pathway Garden" which stands as a permanent living memorial to these students and their families. The City of Seattle public park Soundview Terrace was renovated in honor of the 4 Pearson and the 6 Clemetson family members, all Flight 261 victims from the same Seattle neighborhood of Queen Anne. The park's playground was named "Rachel's Playground" in honor of 6 year old Rachel Pearson who lived nearby and often played at the park.
The Alaska Airlines flight 261 crash has appeared in various advance fee fraud
("419") email scams. In these scams, a scammer uses the name of someone who died in the crash to lure unsuspecting victims into sending money to the scammer by claiming the crash victim left huge amounts of unclaimed money in a foreign bank account. The names of Morris Thompson
and Ronald and Joyce Lake were used in schemes unrelated to them.
As of November 2011, Flight 261 no longer exists. The flight route designation for this route is now Flight 221. Alaska Airlines continues to operate the Puerto Vallarta-San Francisco-Seattle/Tacoma route; the airline also operates the Puerto Vallarta-Seattle/Tacoma route nonstop as Flight 203. The airline also retired all of its MD-80s in 2008 and
now operates all Boeing 737 aircraft.
Alaska Airlines
Alaska Airlines is an airline based in the Seattle suburb of SeaTac, Washington in the United States. The airline originated in 1932 as McGee Airways. After many mergers with and acquisitions of other airlines, including Star Air Service, it became known as Alaska Airlines in 1944...
Flight 261, a McDonnell Douglas MD-83 aircraft, experienced a fatal accident on January 31, 2000 at the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
about 2.7 miles (4.3 km) north of Anacapa Island
Anacapa Island
Anacapa Island is a small volcanic island located about off the coast of Port Hueneme, California, in Ventura County. The Island is composed of a series of narrow islets six miles long, running in a mostly east-west orientation, five miles east of Santa Cruz Island...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. The two pilots, three cabin crewmembers, and 83 passengers on board were killed and the aircraft was destroyed. It was the highest ever death toll of any aviation accident involving a McDonnell Douglas MD-83. Alaska 261 was a scheduled international passenger flight from Lic. Gustavo Díaz Ordaz International Airport
Lic. Gustavo Díaz Ordaz International Airport
Licenciado Gustavo Díaz Ordaz International Airport is an international airport located at Puerto Vallarta, Jalisco in Mexico. Located at the Pacific Ocean coast, it receives thousands of tourists all year. It handled 2,645,300 passengers in 2009 and 2,735,300 in 2010...
in Puerto Vallarta
Puerto Vallarta
Puerto Vallarta is a Mexican balneario resort city situated on the Pacific Ocean's Bahía de Banderas.The 2010 census reported Puerto Vallarta's population as 255,725 making it the sixth-largest city in the state of Jalisco...
, Mexico, to Seattle-Tacoma International Airport
Seattle-Tacoma International Airport
The Seattle–Tacoma International Airport , also known as Sea–Tac Airport or Sea–Tac , is an American airport located in SeaTac, Washington, at the intersections of State Routes 99 and 509 and 518, about west of Interstate 5...
in Seattle, Washington
Seattle, Washington
Seattle is the county seat of King County, Washington. With 608,660 residents as of the 2010 Census, Seattle is the largest city in the Northwestern United States. The Seattle metropolitan area of about 3.4 million inhabitants is the 15th largest metropolitan area in the country...
, with an intermediate stop planned at San Francisco International Airport
San Francisco International Airport
San Francisco International Airport is a major international airport located south of downtown San Francisco, California, United States, near the cities of Millbrae and San Bruno in unincorporated San Mateo County. It is often referred to as SFO...
in San Francisco, California
San Francisco, California
San Francisco , officially the City and County of San Francisco, is the financial, cultural, and transportation center of the San Francisco Bay Area, a region of 7.15 million people which includes San Jose and Oakland...
.
The subsequent investigation by the National Transportation Safety Board determined that inadequate maintenance led to excessive wear and catastrophic failure of a critical flight control system during flight. The probable cause was stated to be "a loss of airplane pitch control resulting from the in-flight failure of the horizontal stabilizer
Tailplane
A tailplane, also known as horizontal stabilizer , is a small lifting surface located on the tail behind the main lifting surfaces of a fixed-wing aircraft as well as other non-fixed wing aircraft such as helicopters and gyroplanes...
trim system jackscrew
Jackscrew
A jackscrew is a type of jack which is operated by turning a leadscrew. In the form of a screw jack it is commonly used to lift heavy weights such as the foundations of houses, or large vehicles.-Advantages:...
assembly's acme
Acme thread form
Trapezoidal thread forms are screw thread profiles with trapezoidal outlines. They are the most common forms used for leadscrews . They offer high strength and ease of manufacture. They are typically found where large loads or high accuracy are required, as in a vise or the leadscrew of a lathe...
nut
Screw thread
A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread...
threads. The thread failure was caused by excessive wear resulting from Alaska Airlines
Alaska Airlines
Alaska Airlines is an airline based in the Seattle suburb of SeaTac, Washington in the United States. The airline originated in 1932 as McGee Airways. After many mergers with and acquisitions of other airlines, including Star Air Service, it became known as Alaska Airlines in 1944...
's insufficient lubrication of the jackscrew assembly."
Passengers
50 people on board the plane were bound for Seattle. They were 47 passengers and the three crew members. Of the remaining 36 passengers and the remaining two crew members, most of them were headed for San Francisco. Of the passengers, 1 was Mexican and 1 was British; the rest were US citizens.Of the occupants, at least 35, including 12 employees, were connected to Alaska Airlines or Horizon Air
Horizon Air
Horizon Air Industries, Inc. is a regional low-cost airline based in SeaTac, Washington, United States. It is the eighth largest regional airline in the USA, serving 52 cities in the United States, Canada and Mexico....
in some manner, leading many airline employees to mourn for the losses in the crash. Alaska Airlines stated that, during slower traveling days, it was common for employees to fill seats that would have otherwise been empty. Bouquets of flowers started arriving at the company's headquarters in SeaTac, Washington
SeaTac, Washington
SeaTac is an American city in southern King County, Washington, and an outlying suburb of Seattle, Washington. Incorporated in February 1990, the City of SeaTac is ten square miles in area and has a population of 26,909 according to the 2010 census...
the day after the crash occurred.
Notable passengers
- Jean Gandesbery, author of Seven Mile Lake, died with her husband Robert Gandesbery
- Morris ThompsonMorris ThompsonMorris Thompson was an Alaska Native leader, American businessman and political appointee working on matters related to Alaska Natives.-Early life and career:...
, Commissioner of the Bureau of Indian AffairsBureau of Indian AffairsThe Bureau of Indian Affairs is an agency of the federal government of the United States within the US Department of the Interior. It is responsible for the administration and management of of land held in trust by the United States for Native Americans in the United States, Native American...
from 1973 to 1976, died with his wife Thelma and daughter Sheryl. - Tom Stockley, wine columnist for The Seattle TimesThe Seattle TimesThe Seattle Times is a newspaper serving Seattle, Washington, US. It is the largest daily newspaper in the state of Washington. It has been, since the demise in 2009 of the printed version of the rival Seattle Post-Intelligencer, Seattle's only major daily print newspaper.-History:The Seattle Times...
. - Cynthia Oti, a financial talk show host at San Francisco's KSFO-AM.
Initial flight segment
Alaska 261 departed from Puerto Vallarta at 1:37 p.m. PST, and climbed to its intended cruising altitude of flight levelFlight level
A Flight Level is a standard nominal altitude of an aircraft, in hundreds of feet. This altitude is calculated from the International standard pressure datum of 1013.25 hPa , the average sea-level pressure, and therefore is not necessarily the same as the aircraft's true altitude either...
310 (31,000 ft). Approximately 2 hours into the flight, the flight crew, consisting of captain Ted Thompson, 53 and first officer William "Bill" Tansky, 57, first contacted the airline's dispatch and maintenance control facilities in SeaTac, Washington
SeaTac, Washington
SeaTac is an American city in southern King County, Washington, and an outlying suburb of Seattle, Washington. Incorporated in February 1990, the City of SeaTac is ten square miles in area and has a population of 26,909 according to the 2010 census...
, and on a shared company radio with operations and maintenance facilities at Los Angeles International Airport
Los Angeles International Airport
Los Angeles International Airport is the primary airport serving the Greater Los Angeles Area, the second-most populated metropolitan area in the United States. It is most often referred to by its IATA airport code LAX, with the letters pronounced individually...
(LAX) discussed a jammed horizontal stabilizer and a possible diversion to LAX. The jammed stabilizer prevented operation of the trim system, which normally would make slight adjustments to the flight control surfaces to keep the plane stable in flight. At their cruising altitude and speed the position of the jammed stabilizer required the pilots to pull on their controls
Yoke (aircraft)
A yoke, alternatively known as control column, is a device used for piloting in most fixed-wing aircraft.- Principle :The aviator uses the yoke to control the attitude of the plane, usually in both pitch and roll. Rotating the control wheel controls the ailerons and the roll axis...
with approximately 10 pounds (44N) of force to keep level. Neither the flight crew, nor company maintenance, were able to determine the cause of the jam. Repeated attempts to overcome the jam with the primary and alternate trim systems were unsuccessful
During this time the flight crew had several discussions with the company dispatcher about whether to divert to Los Angeles, or continue on as planned to San Francisco. Ultimately the pilots chose to divert. Later the NTSB found that while "the flight crew's decision to divert the flight to Los Angeles...was prudent and appropriate", nonetheless "Alaska Airlines dispatch personnel appear to have attempted to influence the flight crew to continue to San Francisco...instead of diverting to Los Angeles." Cockpit Voice Recorder
Cockpit voice recorder
A cockpit voice recorder , often referred to as a "black box", is a flight recorder used to record the audio environment in the flight deck of an aircraft for the purpose of investigation of accidents and incidents...
(CVR) transcripts indicate that the dispatcher was concerned about the effect on the schedule ("flow") should the flight divert.
First dive and recovery
At 4:09 p.m., the flight crew was able to unjam the horizontal stabilizer with the primary trim system, however, upon being freed, it quickly moved to an extreme "nose-down" position, forcing the aircraft into a dive. Alaska 261 went from about 31,500 feet to between 23,000 and 24,000 feet in around 80 seconds. Both pilots struggled together to regain control of the aircraft, and only by exerting a pulling force of 130 to 140 pounds (59.1 to 63.6 kg) on the controls were the flight crew able to arrest the 6,000 foot-per minute descent of the aircraft and stabilize themselves at approximately 24,400 feet.Alaska 261 informed air traffic control
Air traffic control
Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...
(ATC) of their control problems. After the flight crew stated their intention to land at LAX, ATC enquired if they wanted to proceed to a lower altitude in preparation for approach. The captain replied: "I need to get down to about ten, change my configuration, make sure I can control the jet and I'd like to do that out here over the bay if I may." Later, during the public hearings into the accident, the request by the pilot not to overfly populated areas was specifically commended by NTSB board members. During this time the flight crew considered, and rejected, any further attempts to correct the runaway trim. They proceeded to descend to a lower altitude and started to configure the aircraft for landing at LAX.
Second dive and crash
Beginning at 4:19 p.m., the CVR recorded the sounds of at least four distinct "thumps", followed 17 seconds later by an "extremely loud noise". The aircraft rapidly pitched over into a dive. Several aircraft in the vicinity had been alerted by ATC to maintain visual contact with the stricken jet and they immediately contacted the controller. One pilot radioed "that plane has just started to do a big huge plunge"; another reported, "Yes sir, ah, I concur he is, uh, definitely in a nose down, uh, position descending quite rapidly." ATC then tried to contact Alaska 261. The crew of a SkywestSkywest Airlines
Skywest Airlines Pty Ltd is a regional airline company based in Perth, Western Australia, Australia; servicing key towns in the state of Western Australia, Darwin, Northern Territory and Melbourne, Victoria; as well as charter flights to Bali, Indonesia....
airliner reported "He's, uh, definitely out of control" Although the CVR captured the co-pilot saying "Mayday
Mayday (distress signal)
Mayday is an emergency procedure word used internationally as a distress signal in voice procedure radio communications. It derives from the French venez m'aider, meaning "come help me"....
", no radio communications were received from the flight crew during the final event.
The CVR transcript reveals the pilots' continuous attempts for the duration of the dive to regain control of the aircraft. At one point, unable to raise the nose, they attempted to fly the aircraft "upside-down". However the aircraft was beyond recovery; it descended inverted and nose-down about 18,000 feet in 81 seconds, a descent rate exceeding 13,300 feet per minute, before hitting the ocean at high speed. At this time, pilots from aircraft flying in the same area reported in, with one SkyWest Airlines
Skywest Airlines
Skywest Airlines Pty Ltd is a regional airline company based in Perth, Western Australia, Australia; servicing key towns in the state of Western Australia, Darwin, Northern Territory and Melbourne, Victoria; as well as charter flights to Bali, Indonesia....
pilot saying, "and he's just hit the water," meaning the plane had crashed into the ocean. Another reported, "Yeah sir, he, uh, he, uh, hit the water, he's, uh, down." Everyone on board died when the plane struck the water, and the aircraft was destroyed upon impact.
Wreckage recovery and analysis
Side-scan sonar
Side-scan sonar is a category of sonar system that is used to efficiently create an image of large areas of the sea floor...
, remotely operated vehicle
Remotely operated vehicle
A remotely operated vehicle is a tethered underwater vehicle. They are common in deepwater industries such as offshore hydrocarbon extraction. An ROV may sometimes be called a remotely operated underwater vehicle to distinguish it from remote control vehicles operating on land or in the air. ROVs...
s, and a commercial fishing trawler, workers recovered about 85% of the fuselage (including the tail section) and a majority of the wings. In addition, both engines, as well as the Flight Data Recorder
Flight data recorder
A flight data recorder is an electronic device employed to record any instructions sent to any electronic systems on an aircraft. It is a device used to record specific aircraft performance parameters...
(FDR) and CVR were retrieved. All wreckage was unloaded at Port Hueneme, California for examination and documentation. Both the horizontal stabilizer trim system jackscrew (also referred to as "acme screw"), and the corresponding acme nut, which the jackscrew turns through, were retrieved. As the jackscrew rotates it moves up or down through the (fixed) acme nut. This up and down motion moves the horizontal stabilizer for the trim system. The jackscrew was found with metallic filaments wrapped around it; these were later determined to be remnants of the threads from the acme nut.
Later analysis estimated that 90% of the threads in the acme nut had been previously worn away, and that they were then completely sheared off during the accident flight. Once the threads failed, the horizontal stabilizer assembly was then subject to aerodynamic forces that it could not withstand, and ultimately failed. Based on the time since the last inspection of the jackscrew assembly, the NTSB determined that the wear had occurred at a much faster than average rate (0.012 inch per 1,000 flight hours, when the expected wear was 0.001 inch per 1,000 flight hours). The NTSB considered a number of potential reasons for this excessive wear, including the substitution by Alaska Airlines (with the approval of the aircraft manufacturer Boeing
Boeing
The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...
) of Aeroshell 33 grease instead of the previously approved lubricant, Mobilgrease 28. The use of Aeroshell 33 was found not to be a factor in this accident. Insufficient lubrication of the components was also considered as a reason for the wear. Examination of the jackscrew and acme nut revealed that no effective lubrication was present on these components at the time of the accident. Ultimately, the lack of lubrication and resultant excessive wear of the acme nut threads were determined to be the direct causes of the accident.
NTSB Animation: Longitudinal Trim System Description and Failure Sequence (.wmv file)
Identification of passengers
Crash victims were identified using fingerprints, dental records, tattoos, personal items, and anthropological examinations.Inadequate lubrication and end play checks
The investigation then proceeded to examine why scheduled maintenance had failed to adequately lubricate the jackscrew assembly. In interviews with the Alaska Airlines SFO mechanic who last performed the lubrication it was revealed that the task took about 1 hour, whereas the aircraft manufacturer estimated the task should take 4 hours. This and other evidence suggested to the NTSB that "the SFO mechanic who was responsible for lubricating the jackscrew assembly in September 1999 did not adequately perform the task." Laboratory tests indicated that the excessive wear of jackscrew assembly could not have accumulated in just the 4 months period between the September 1999 maintenance and the accident flight. Therefore, the NTSB concluded that "more than just the last lubrication was missed or inadequately performed."In order to monitor wear on the jackscrew assembly a periodic maintenance inspection called an "end play check" was used. The NTSB examined why the last end play check on the accident aircraft in September 1997 did not uncover excessive wear. The investigation found that Alaska Airlines had fabricated tools to be used in the end play check that did not meet the manufacturer's requirements. Testing revealed that the non-standard tools ("restraining fixtures") used by Alaska Airlines could result in inaccurate measurements, and that it was possible that if accurate measurements had been obtained at the time of the last inspection, these measurements would have indicated the excessive wear and the need for the replacement of the affected components.
Extension of maintenance intervals
Between 1985 and 1996 Alaska Airlines progressively increased the period in between jackscrew lubrication as well as end play checks with the approval of the Federal Aviation AdministrationFederal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...
(FAA). Since each lubrication or end play check subsequently not conducted had represented an opportunity to adequately lubricate the jackscrew or detect excessive wear, the NTSB examined the justification of these extensions. In the case of extended lubrication intervals, the investigation was not able to determine what information, if any, was presented by Alaska Airlines to the FAA prior to 1996. Testimony from an FAA inspector regarding an extension granted in 1996 was that Alaska Airlines submitted documentation from Boeing as justification for their extension.
End play checks were conducted during a periodic comprehensive airframe overhaul process called a "C-check". Testimony from the director of reliability and maintenance programs of Alaska Airlines was that a data analysis package based on the maintenance history of five sample aircraft was submitted to the FAA to justify the extended period between C-checks. Individual maintenance tasks (such as the end play check) were not separately considered in this extension. The NTSB found that "Alaska Airlines' end play check interval extension should have been, but was not, supported by adequate technical data to demonstrate that the extension would not present a potential hazard."
FAA oversight
A special inspection conducted by the NTSB in April 2000 of Alaska Airlines uncovered widespread significant deficiencies that "the FAA should have uncovered earlier." The investigation concluded that "FAA surveillance of Alaska Airlines had been deficient for at least several years." The NTSB noted that in July 2001, an FAA panel determined that Alaska Airlines had corrected the previously identified deficiencies. However several factors led the Board to question "the depth and effectiveness of Alaska Airlines corrective actions" and "the overall adequacy of Alaska Airlines' maintenance program."Systematic problems were identified by the investigation in the FAA's oversight of maintenance programs, including inadequate staffing, its approval process of maintenance interval extensions, and the aircraft certification requirements.
Aircraft design and certification issues
The jackscrew assembly was designed with two independent threads, each of which was strong enough to withstand the forces placed on it. Maintenance procedures such as lubrication and end play checks were to catch any excessive wear before it progressed to a point of failure of the system. The aircraft designers assumed that at least one set of threads would always be present to carry the loads placed on it, therefore the effects of catastrophic failure of this system were not considered, and no "fail-safeFail-safe
A fail-safe or fail-secure device is one that, in the event of failure, responds in a way that will cause no harm, or at least a minimum of harm, to other devices or danger to personnel....
" provisions were needed.
In order for this design component to be approved ("certified") by the FAA without any fail-safe provision, a failure had to be considered "extremely improbable". This was defined as "having a probability on the order of 1 x 10-9 or less each flight hour." However the accident showed that certain wear mechanisms could affect both sets of threads, and that the wear might not be detected. The NTSB determined that the design of "the horizontal stabilizer jackscrew assembly did not account for the loss of the acme nut threads as a catastrophic single-point failure mode."
Jackscrew design improvement
In 2001, NASA recognized the risk to its hardware (such as the Space Shuttle) attendant upon use of similar jackscrews. An engineering fix developed by engineers of NASA and United Space Alliance promises to make progressive failures easy to see and thus complete failures of a jackscrew almost impossible.Conclusions
In addition to the probable cause, the NTSB found the following contributing factors:- Alaska Airlines' extension of its lubrication interval for its McDonnell Douglas MD-80 horizontal stabilizer components, and the FAA's approval of that extension, the last of which was based on Boeing's extension of the recommended lubrication interval increased the likelihood that a missed or inadequate lubrication would result in excessive wear of jackscrew assembly acme nut threads and, therefore, was a direct cause of the excessive wear and contributed to the Alaska Airlines flight 261 accident.
- Alaska Airlines's extended end play check interval and the FAA's approval of that extension, which allowed the excessive wear of the acme nut threads to progress to failure without the opportunity for detection
- The absence on the McDonnell Douglas MD-80 of a fail-safe mechanism to prevent the catastrophic effects of total acme nut loss
During the course of the investigation, and later in its final report, the NTSB issued a total of 24 safety recommendations, covering maintenance, regulatory oversight, and aircraft design issues. More than half of these were directly related to jackscrew lubrication and end play measurement. Also included was a recommendation that pilots were to be instructed that in the event of a flight control system malfunction they should not attempt corrective procedures beyond those specified in the checklist procedures, and in particular in the event of a horizontal stabilizer trim control system malfunction the primary and alternate trim motors should not be activated, and if unable to correct the problem through the checklists they should land at the nearest suitable airport.
In NTSB board member John J. Goglia's statement for the final report, which was concurred with by all three other board members, he wrote:
Aftermath
After the crash occurred, Alaska AirlinesAlaska Airlines
Alaska Airlines is an airline based in the Seattle suburb of SeaTac, Washington in the United States. The airline originated in 1932 as McGee Airways. After many mergers with and acquisitions of other airlines, including Star Air Service, it became known as Alaska Airlines in 1944...
management said that it hoped to handle the aftermath in a manner similar to that done by Swissair
Swissair
Swissair AG was the former national airline of Switzerland.It was formed from a merger between Balair and Ad Astra Aero , in 1931...
after the Swissair Flight 111
Swissair Flight 111
Swissair Flight 111 was a Swissair McDonnell Douglas MD-11 on a scheduled airline flight from John F. Kennedy International Airport in New York City, United States to Cointrin International Airport in Geneva, Switzerland...
accident, as opposed to the manner that TWA
Twa
The Twa are any of several hunting peoples of Africa who live interdependently with agricultural Bantu populations, and generally hold a socially subordinate position: They provide the farming population with game in exchange for agricultural products....
handled the aftermath of TWA Flight 800
TWA Flight 800
Trans World Airlines Flight 800 , a Boeing 747-131, exploded and crashed into the Atlantic Ocean near East Moriches, New York, on July 17, 1996, at about 20:31 EDT, 12 minutes after takeoff, killing all 230 persons on board. At the time, it was the second-deadliest U.S...
; in other words, to provide timely information and compassion to the families of victims.
The families of the victims approved the construction of a memorial sundial
Sundial
A sundial is a device that measures time by the position of the Sun. In common designs such as the horizontal sundial, the sun casts a shadow from its style onto a surface marked with lines indicating the hours of the day. The style is the time-telling edge of the gnomon, often a thin rod or a...
that was placed at Port Hueneme. The sundial was designed by Santa Barbara artist Bud Bottoms to cast a shadow on a memorial plaque at 4:22 p.m. each January 31.
For their actions during the emergency, Captain Ted Thompson and First Officer Bill Tansky were awarded the Airline Pilots Association Gold Medal for Heroism, the only time the award has been given posthumously.
Both Boeing and Alaska Airlines eventually conceded liability for the crash, and all but one of the lawsuits brought by surviving family members were settled out-of-court before going to trial. Candy Hatcher of the Seattle Post-Intelligencer
Seattle Post-Intelligencer
The Seattle Post-Intelligencer is an online newspaper and former print newspaper covering Seattle, Washington, United States, and the surrounding metropolitan area...
said "Many lost faith in Alaska Airlines, a homegrown company that had taken pride in its safety record and billed itself as a family airline."
Two victims from Alaska 261 were falsely named in paternity suits as the fathers of children in Guatemala in an attempt to gain insurance and settlement money. DNA testing revealed these claims to be false.
This crash was featured in a 2004 episode of Discovery Channel (Canada)
Discovery Channel
Discovery Channel is an American satellite and cable specialty channel , founded by John Hendricks and distributed by Discovery Communications. It is a publicly traded company run by CEO David Zaslav...
's Mayday
Mayday (TV series)
Mayday, also known as Air Crash Investigation in the United Kingdom, Australia and Asia and Air Emergency and Air Disasters in the United States, is a Canadian documentary television programme produced by Cineflix investigating air crashes, near-crashes and other disasters...
television program (also known as Air Crash Investigation and also known as Air Emergency), titled Cutting Corners or Fatal Error.
The Ted Thompson/Bill Tansky Scholarship Fund was named after the two cockpit flight crew members.
Many residents of the City of Seattle had been affected by the disaster. As part of a memorial vigil in the year 2000, a column of light was beamed from the top of the Space Needle
Space Needle
The Space Needle is a tower in Seattle, Washington and is a major landmark of the Pacific Northwest region of the United States and a symbol of Seattle. Located at the Seattle Center, it was built for the 1962 World's Fair, during which time nearly 20,000 people a day used the elevators, with over...
. Students and faculty at the John Hay Elementary School in Queen Anne, Seattle held a memorial for four Hay students who died in the crash. In April, 2001, John Hay Elementary dedicated the "John Hay Pathway Garden" which stands as a permanent living memorial to these students and their families. The City of Seattle public park Soundview Terrace was renovated in honor of the 4 Pearson and the 6 Clemetson family members, all Flight 261 victims from the same Seattle neighborhood of Queen Anne. The park's playground was named "Rachel's Playground" in honor of 6 year old Rachel Pearson who lived nearby and often played at the park.
The Alaska Airlines flight 261 crash has appeared in various advance fee fraud
Advance fee fraud
An advance-fee fraud is a confidence trick in which the target is persuaded to advance sums of money in the hope of realizing a significantly larger gain...
("419") email scams. In these scams, a scammer uses the name of someone who died in the crash to lure unsuspecting victims into sending money to the scammer by claiming the crash victim left huge amounts of unclaimed money in a foreign bank account. The names of Morris Thompson
Morris Thompson
Morris Thompson was an Alaska Native leader, American businessman and political appointee working on matters related to Alaska Natives.-Early life and career:...
and Ronald and Joyce Lake were used in schemes unrelated to them.
As of November 2011, Flight 261 no longer exists. The flight route designation for this route is now Flight 221. Alaska Airlines continues to operate the Puerto Vallarta-San Francisco-Seattle/Tacoma route; the airline also operates the Puerto Vallarta-Seattle/Tacoma route nonstop as Flight 203. The airline also retired all of its MD-80s in 2008 and
now operates all Boeing 737 aircraft.
External links
- Archive of Alaska Airlines news reports about 261
- Main NTSB Alaska Airlines Flight 261 investigation page
- The NTSB's full report
- Families of Alaska Airlines Flight 261
- "Navy expands search for debris at Alaska Airlines Flight 261 crash scene," United States NavyUnited States NavyThe United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
- Applying Lessons Learned from Accidents, Alaska Airlines Flight 261 - Informative analysis at faa.gov, with technical diagrams and photos
- Seattle Post-Intelligencer special report