Alaska Airlines Flight 261

The aircraft involved in the accident was a McDonnell-Douglas MD-83, serial number 53077, and registered as N963AS. The aircraft was manufactured and delivered new to Alaska Airlines in 1992 and had logged 26,584 flight hours and 14,315 cycles before the crash.[2][3]

The pilots of Flight 261 were both highly experienced aviators.[4] Captain Edward (Ted) Thompson, 53, had accrued 17,750 flight hours, and had more than 4,000 hours experience flying MD-80s.[1]^:10–11 First Officer William (Bill) Tansky, 57, had accumulated 8,140 total flight hours, including about 8,060 hours as first officer in the MD-80.[1]^:11 Neither pilot had been involved in an accident or incident prior to the crash.[1] There were three Seattle-based flight attendants on board.[5]

The three flight attendants and 47 of the passengers on board the plane were bound for Seattle.[6] 32 passengers were traveling to San Francisco; three were bound for Eugene, Oregon; and three passengers were headed for Fairbanks, Alaska.[7] Of the passengers, one was Mexican and one was British, with all others being American citizens.[8]

At least 35 occupants of Flight 261 were connected in some manner with Alaska Airlines or its sister carrier Horizon Air, including twelve actual employees,[9] leading many of the airlines' personnel to mourn for those lost in the crash.[10] Alaska Airlines stated that it was commonplace, on less busy flights, for employees to fill seats that would otherwise have been left empty. Bouquets of flowers started arriving at the company's headquarters in SeaTac, Washington, the day after the crash.[11]

Final flight path of Alaska 261

Alaska 261 departed from Puerto Vallarta at 13:37 PST (21:37 UTC), and climbed to its intended cruising altitude of flight level 310 (31,000 feet or 9,400 meters). The plane was scheduled to land at San Francisco International Airport. Some time before 15:49 (23:49 UTC), the flight crew contacted the airline's dispatch and maintenance control facilities in SeaTac, Washington, on a company radio frequency shared with operations and maintenance facilities at Los Angeles International Airport (LAX), to discuss a jammed horizontal stabilizer and a possible diversion to LAX.[1] The jammed stabilizer prevented operation of the trim system, which would normally 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 yokes with approximately 10 pounds (44 N) of force to keep level.[1] Neither the flight crew, nor company maintenance, could determine the cause of the jam.[1] Repeated attempts to overcome the jam with the primary and alternate trim systems were unsuccessful.[1]

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.[1] Later, the NTSB found that while "the flight crew's decision to divert the flight to Los Angeles [...] was prudent and appropriate", "Alaska Airlines dispatch personnel appear to have attempted to influence the flight crew to continue to San Francisco [...] instead of diverting to Los Angeles".[1]^:137 Cockpit voice recorder (CVR) transcripts indicate that the dispatcher was concerned about the effect on the schedule ("flow"), should the flight divert.[1]^:195–197

At 16:09 (00:09 UTC), the flight crew successfully unjammed 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 an almost vertical nosedive. The plane dropped from about 31,500 ft (9,600 m) to between 23,000 and 24,000 ft (7,000 and 7,300 m) in around 80 seconds.[1] Both pilots struggled together to regain control of the aircraft, and only by pulling with 130 to 140 pounds (580 to 620 N) on the controls did the flight crew stop the 6,000 ft/min (1,800 m/min) descent of the aircraft and stabilize the MD-83 at approximately 24,400 ft (7,400 m).[1]

Alaska 261 informed air traffic control of their control problems. After the flight crew stated their intention to land at LAX, ATC asked whether they wanted to proceed to a lower altitude in preparation for approach.[1] 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".[1]^:8 Later, during the public hearings into the accident, the request by the pilot not to overfly populated areas was mentioned.[12]^:6–9 During this time, the flight crew considered, and rejected, any further attempts to correct the runaway trim. They descended to a lower altitude and started to configure the aircraft for landing at LAX.[1]

Beginning at 16:19 (00:19 UTC), the CVR recorded the sounds of at least four distinct "thumps" followed 17 seconds later by an "extremely loud noise", as the overstrained jackscrew assembly failed completely and the jackscrew separated from the acme nut holding it in place. The aircraft rapidly pitched over into a dive.[1] The crippled aircraft had been given a block altitude,[13] and several aircraft in the vicinity had been alerted by ATC to maintain visual contact with the stricken jet. These immediately contacted the controller;[14] 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."[14] ATC then tried to contact the plane. The crew of a SkyWest airliner reported: "He's, uh, definitely out of control."[14] Although the CVR captured the co-pilot saying "mayday", no radio communications were received from the flight crew during the final event.[1]^:9[14]

The CVR transcript reveals the pilots' continuous attempts for the duration of the dive to regain control of the aircraft.[1]^:9 At one point, unable to raise the nose, they attempted to fly the aircraft upside-down in an effort to maintain control.[1] However, the aircraft was far beyond recovery; it descended inverted and nose-down about 18,000 feet (5,500 m) in 81 seconds (151 mph; 243 km/h). A few seconds before 16:22 (00:22 UTC), Flight 261 impacted the Pacific Ocean at high speed about 14 miles (23 kilometers; 12 nautical miles) offshore, between the coastal city of Port Hueneme, California, and Anacapa Island. 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". Another reported: "Ah, yes sir he ah, he ah, hit the water. He's ah down."[14][15] The aircraft was destroyed by the impact forces, and all occupants on board were killed by blunt force impact trauma.[1]

Recovered jackscrew – the spiral "wire" wrapped around the threaded portion is the remnants of the internal screw thread stripped from the acme nut

Deepak Joshi (left) of the NTSB and John Scarola of Alaska Airlines prepare the Flight Data Recorder for transport from the MV Kellie Chouest on Feb 3, 2000

Using side-scan sonar, remotely operated vehicles, and a commercial fishing trawler, workers recovered about 85% of the fuselage (including the tail section) and a majority of the wing components. [16] In addition, both engines, as well as the flight data recorder (FDR) and CVR were retrieved. All wreckage recovered from the crash site was unloaded at the Seabee's Naval Construction Battalion Center Port Hueneme, California, for examination and documentation by NTSB investigators.[1] Both the horizontal stabilizer trim system jackscrew (also referred to as "acme screw") and the corresponding acme nut, which the jackscrew turns through, were found. The jackscrew was constructed from case-hardened steel and is 22 inches (56 cm) long and 1.5 inches (3.8 cm) in diameter.[1][17] The acme nut was constructed from a softer copper alloy containing aluminum, nickel, and bronze.[17][1] As the jackscrew rotates, it moves up or down through the (fixed) acme nut, and this linear motion moves the horizontal stabilizer for the trim system. Upon subsequent examination, the jackscrew was found to have metallic filaments wrapped around it, which were later determined to be the remains of the acme-nut thread.[1]

Later analysis estimated that 90% of the thread in the acme nut had already worn away previously, and that it had finally stripped out during the flight while en route to San Francisco. Once the thread had failed, the horizontal stabilizer assembly was then subjected to aerodynamic forces that it was not designed to withstand, leading to complete failure of the overstressed stabilizer assembly.[1] Based on the time since the last inspection of the jackscrew assembly, the NTSB determined that the acme-nut thread had deteriorated at 0.012 inches (0.30 mm) per 1000 flight‑hours, much faster than the expected wear of 0.001 inches (0.025 mm) per 1000 flight‑hours.[1] Over the course of the investigation, the NTSB considered a number of potential reasons for the substantial amount of deterioration of the nut thread on the jackscrew assembly, including the substitution by Alaska Airlines (with the approval of the aircraft manufacturer McDonnell Douglas) 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.[1] 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.[18] Ultimately, the lack of lubrication of the acme-nut thread and the resultant excessive wear were determined to be the direct causes of the accident.[1]

Due to the extreme impact forces and subsequent loss of any occupiable space within the passenger cabin, only a few bodies were found intact,[4] and none were visually identifiable. All occupants were identified using fingerprints, dental records, tattoos, personal items, and anthropological examination.[19]

The investigation then proceeded to examine why scheduled maintenance had failed to adequately lubricate the jackscrew assembly. In interviews with the Alaska Airlines mechanic at San Francisco International Airport (SFO) who last performed the lubrication it was revealed that the task took about one hour, whereas the aircraft manufacturer estimated the task should take four hours.[1] 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".[1] Laboratory tests indicated that the excessive wear of jackscrew assembly could not have accumulated in just the four-month period between the September 1999 maintenance and the accident flight.[1] Therefore, the NTSB concluded that "more than just the last lubrication was missed or inadequately performed".[1]

A periodic maintenance inspection called an "end-play check" was used to monitor wear on the jackscrew assembly. 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.[1] 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 to replace the affected components.[1]

Between 1985 and 1996, Alaska Airlines progressively increased the period in between both jackscrew lubrication and end-play checks, with the approval of the Federal Aviation Administration (FAA).[1] 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 could not determine what information, if any, was presented by Alaska Airlines to the FAA prior to 1996.[1] Testimony from an FAA inspector regarding an extension granted in 1996 was that Alaska Airlines submitted documentation from McDonnell Douglas as justification for their extension.[1]

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.[1] 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".[1]

A special inspection conducted by the NTSB in April 2000 of Alaska Airlines uncovered widespread significant deficiencies that "the FAA should have uncovered earlier".[1] The investigation concluded that "FAA surveillance of Alaska Airlines had been deficient for at least several years".[1] 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".[1]

Systemic 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.[1]

The jackscrew assembly was designed with two independent threads, each of which was strong enough to withstand the forces placed on it.[1] 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-safe" provisions were needed.

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 1×10⁻⁹ or less each flight hour".[1] 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".[1]

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 less likely.[20]

In 1998, an Alaska Airlines mechanic named John Liotine, who worked in the Alaska Airlines maintenance center in Oakland, California, told the Federal Aviation Administration that supervisors were approving records of maintenance that they were not allowed to approve or that indicated work had been completed when, in fact, it had not. Liotine began working with federal investigators by secretly audio recording his supervisors. On December 22, 1998, federal authorities raided an Alaska Airlines property and seized maintenance records. In August 1999 Alaska Airlines put Liotine on paid leave,[21] and in 2000 Liotine filed a libel suit against the airline. The crash of AS261 became a part of the federal investigation against Alaska Airlines because in 1997, Liotine had recommended that the jackscrew and gimbal nut of the accident aircraft be replaced, but had been overruled by another supervisor.[22] In December 2001 federal prosecutors stated that they were not going to file criminal charges against Alaska Airlines. Around that time Alaska Airlines agreed to settle the libel suit by paying about $500,000; as part of the settlement, Liotine resigned.[21]

• Jean Gandesbery, author of the book Seven Mile Lake: Scenes from a Minnesota Life,[39] died alongside her husband, Robert.[40][34]
• Cynthia Oti, an investment broker and financial talk show host at San Francisco's KSFO-AM.[34]
• Tom Stockley, wine columnist for The Seattle Times.[34]
• Morris Thompson, commissioner of the Bureau of Indian Affairs from 1973 to 1976, died alongside his wife Thelma and daughter Sheryl.[10][34]