On January 31, 2000, the aviation world was shaken by the tragic events surrounding Alaska Airlines Flight 261.
What was supposed to be a routine flight turned into a catastrophic disaster, leaving investigators and the public grappling with the question: what went wrong?
Flight 261 was operated by the McDonnell-Douglas MD-80, a workhorse of the skies known for its reliability. The relatively new aircraft was delivered to Alaska Airlines in 1992 and had accumulated 26,584 flight hours and undergone 14,315 cycles until the crash.
Crew and Passengers involved in Flight 261
The flight was carrying 83 passengers and five crew members.
The pilots of Flight 261 were very experienced and even had previous military experience. Captain Ted Thompson, aged 53, had accrued 17,750 flight hours, including over 4,000 hours on MD-80s. First Officer William “Bill” Tansky, aged 57, had a total of 8,140 flight hours, with approximately 8,060 hours as a first officer on the MD-80.
January 31, 2000 – accident takes place
Alaska Airlines Flight 261 departed from Puerto Vallarta International Airport (PVR) in Mexico and was scheduled to land at Seattle–Tacoma International Airport (SEA) in the United States, with a planned stop at San Francisco International Airport (SFO).
The aircraft operated without issues in the early stages of the flight. However, the horizontal stabilizer ceased to respond to both autopilot and pilot commands after the airplane reached an altitude of 23,400 feet.
The pilots identified a malfunction in the longitudinal trim system but were unable to ascertain the cause. They contacted the airline’s dispatch and maintenance-control centers to address a possible problem with a jammed horizontal stabilizer and discuss the option of diverting to Los Angeles International Airport (LAX).
The stuck stabilizer prevented the normal operation of the trim system, which typically makes minor adjustments to the flight control surfaces to maintain the aircraft’s stability in flight.
Both the flight crew and the airline’s maintenance team were unable to identify the cause of the jam. Multiple efforts to resolve the issue using both the primary and alternate trim systems proved unsuccessful.
At their altitude and speed, handling the aircraft manually posed no challenge for the crew. After manually piloting for two hours, the crew attempted to engage the autopilot multiple times, but it disengaged each time.
According to the Alaska Airlines MD-80 Stabilizer Inoperative checklist, the autopilot should not be used when the trim systems are not functioning. The flight crew engaged in troubleshooting the trim system by utilizing the trim handles and control wheel trim switches, all while maintaining communication with dispatch and maintenance personnel.
Finally, the flight crew successfully resolved the jammed horizontal stabilizer using the primary trim system.
1st nosedive and recovery
The primary trim motor shifted the jackscrew, releasing the jammed acme nut and enabling the horizontal stabilizer to tilt its leading edge upward until it reached the lower mechanical stop. Once freed, however, it swiftly transitioned to an extreme “nose-down” position, causing the aircraft to enter an almost vertical nosedive.
Within approximately 80 seconds, the plane fell from approximately 31,500 feet (9,600 meters) to a range of 23,000 to 24,000 feet (7,000 to 7,300 meters).
The crew applied control inputs to raise the nose, activated the speed brakes to slow down the rapidly accelerating airspeed, and successfully pulled out of the dive at around 24,000 feet.
Following the recovery, the crew extended the slats and flaps to slow the aircraft, preparing for an emergency landing at LAX. Throughout this process, the airplane was stable and in control.
2nd nosedive and crash
Ten minutes after the first nosedive, the jackscrew assembly experienced a complete failure due to overstrain, causing the jackscrew to separate from the acme nut that held it in place. This led to the failure of the horizontal stabilizer at an altitude of 17,800 feet (5,400 meters), resulting in the aircraft rapidly pitching at -70° into a dive while rolling to the left.
In an attempt to correct the situation, the crew was able to increase the pitch to -28°. However, over the next minute, the crew encountered difficulties rolling the plane, with the aircraft completely inverted and still diving at a -9-degree pitch.
The transcript from the Cockpit Voice Recorder (CVR) reveals the pilots’ efforts to regain control of the aircraft during the dive. It also includes the last words of the pilots: “Ah, here we go,” indicating their realization that they were about to crash.
Despite attempting to maneuver the plane inverted, which briefly slowed its descent, the aircraft had descended too much during the dive, far beyond recovery. Flight 261 crashed into the Pacific Ocean at a high speed. The impact forces led to the destruction of the aircraft, resulting in the fatality of all occupants due to blunt-force impact trauma.
Investigation of Alaska Airlines Flight 261
The subsequent analysis indicated that approximately 90% of the thread in the acme nut had previously worn away, and it ultimately stripped out during the flight en route to San Francisco.
Federal Aviation Administration / Wikimedia
After the thread failure, the horizontal stabilizer assembly experienced aerodynamic forces beyond its design limits, resulting in the total collapse of the stabilizer assembly.
In the end, the accident was directly attributed to the absence of lubrication in the acme-nut thread and the consequent excessive wear.
The National Transportation Safety Board NTSB identified the following factors contributing to the crash of Alaska Airlines Flight 261:
- Alaska Airlines extended the MD-80 stabilizer lubrication interval, approved by the Federal Aviation Administration (FAA), raising the risk of insufficient lubrication and leading to severe acme-nut thread deterioration.
- Alaska Airlines extended the end-play check interval, also FAA-approved, enabling acme-nut threads to deteriorate undetected until failure.
- The MD-80 lacked a fail-safe mechanism to prevent catastrophic consequences from total acme nut loss.
NTSB / Wikimedia
Throughout the investigation and in its final report, the NTSB issued 24 safety recommendations encompassing maintenance, regulatory oversight, and aircraft design matters. Over half of these were specifically tied to jackscrew lubrication and end-play measurement.
Pilots were recommended to strictly follow checklist procedures in the event of a flight-control system malfunction. Specifically, if faced with a horizontal stabilizer trim-control system issue, they were advised not to activate the primary and alternate trim motors. If the problem persisted after following the checklist, landing at the nearest suitable airport was strongly advised.
Julia Brownley / Wikipedia