Aircraft Accident Investigation Analysis Engineering Essay

On January 31, 2000, the National Transportation Safety Board launched a Go Team to Oxnard, California, to get down its probe of the clang of Alaska Airlines flight 261. The McDonnell Douglas MD-83 ( N963AS ) was in path from Puerto Vallarta, Mexico to Seattle, Washington with a halt planned for San Francisco, California. All 83 riders and five crewmembers aboard the MD-80 died when the aircraft crashed into the Pacific Ocean.A

This study explains the accident affecting Alaska Airlines flight 261, the McDonnell DouglasMD-83, which crashed into the Pacific Ocean about 2.7 stat mis north of Anacapa Island, California. Safety issues discussed in this study include lubrication and review of the doodly-squat prison guard assembly, extension of lubrication and stop drama cheque intervals, screw jack assembly inspection and repair processs, the design and enfranchisement of the MD-80 horizontal stabilizer pare control system, Alaska Airlines. Besides the study will discourse the Maintenance plan and Federal Aviation Administration ( FAA ) inadvertence of Alaska Airlines and the safety recommendations addressed to the FAA.

The Accident Flight

Alaska 261 departed from PVR at 1:37 p.m. Pacific criterion clip, and climbed to its intended cruising height of Flight degree ( 31,000 pess ) . Approximately 2 hours into the flight, the flight crew foremost contacted the air hose ‘s despatch and care control installations in SEA and on a shared company wireless with operations and care installations at ( LAX ) to discourse a jam-packed horizontal stabilizer and a possible recreation to LAX. The jam-packed stabilizer prevented operation of the spare system, which usually would do little accommodations to the flight control surfaces to maintain the plane stable in flight. At their cruising height and rush the place of the jam-packed stabilizer required the pilots to draw on their controls with force to maintain degree. Neither the flight crew, nor company care, were able to find the cause of the jam. Repeated efforts to get the better of the jam with the primary and alternate spare systems were unsuccessful.

During this clip the flight crew had several treatments with the company dispatcher about whether to deviate to LAX, or go on on every bit planned to SFO. Ultimately the pilots chose to deviate. Subsequently the NTSB found that “ the flight crew ‘s determination to deviate the flight to Los Angeles… was prudent and appropriate ” , however “ Alaska Airlines despatch forces appear to hold attempted to act upon the flight crew to go on to San Francisco… alternatively of deviating to Los Angeles. ” Cockpit Voice Recorder ( CVR ) transcripts indicate that the starter was concerned about the consequence on the agenda ( “ flux ” ) should the flight divert.

The flight crew was able to un-jam the horizontal stabilizer with the primary trim system, nevertheless upon being freed it rapidly moved to an utmost “ nose-down ” place, coercing the aircraft into a honkytonk. Alaska 261 went from about 31,500 pess to between 23,000 and 24,000 pess in around 80 seconds. Both pilots struggled together to recover control of the aircraft, and by drawing on the controls where the flight crew were able to collar the descent of the aircraft and stabilise themselves at about 24,400 pess.

Alaska 261 informed ( ATC ) of their control jobs. After the flight crew stated their purpose to land at LAX, ATC inquired if they wanted to continue to a lower height in readying for attack. The captain replied: “ I need to acquire down to approximately ten, alter my constellation, make certain I can command the jet and I ‘d wish to make that out here over the bay if I may ( CVR ) . During this clip the flight crew considered, and rejected, any farther efforts to rectify the runaway trim. They proceeded to fall to a lower height and get down to configure the aircraft for set downing at LAX.

The CVR recorded the sounds of at least four distinguishable “ clumps ” , followed 17 seconds subsequently by an “ highly loud noise ” . The aircraft quickly pitched over into a honkytonk. Several aircraft in the locality had been alerted by ATC to keep ocular contact with the afflicted jet and they instantly contacted the accountant. One pilot radioed “ that plane has merely started to make a large immense dip ” , another reported “ Yes sir ah I concur he is uh decidedly in a nose down uh place falling rather quickly ” . ATC so tried to reach Alaska 261. Although the CVR captured the copilot stating “ Mayday ” , no wireless communications were received from the flight crew during the concluding event.

The CVR transcript shows the pilots ‘ uninterrupted efforts for the continuance of the honkytonk to recover control of the aircraft. At one point, unable to raise the nose, they even attempted to wing the aircraft “ inverted ” . However the aircraft was beyond recovery, and fell about 18,000 pess nose-down and inverted for 1 minute, 21 seconds before impacting the ocean at high velocity. There were no subsisters, and the aircraft was destroyed by impact forces.

Flight Crew

The flight crewmembers on Alaska Airlines flight 261 were decently certificated and qualified and had received the preparation and off-duty clip prescribed by Federal ordinances. No grounds indicated any preexisting medical or other status that might hold adversely affected the flight crew ‘s public presentation during the accident flight.

The captain, age 53, was hired by Jet America 29 on August 16, 1982. The captain held an air hose conveyance pilot ( ATP ) certification, issued March 16, 1984, with a type evaluation in the Douglas DC-9. Harmonizing to Alaska Airlines records, the captain had flown about 17,750 entire flight hours, including 10,460 hours as pilot-in-command, of which about 4,150 hours were as pilot-in-command in the MD-80.

The first officer, age 57, was hired by Alaska Airlines on July 17, 1985. He held an ATP certification, issued April 3, 1985, with type evaluations in the DC-9/MD-80, DC-6, and DC-7.

Harmonizing to Alaska Airlines records, the first officer had flown about 8,140 entire flight hours, including about 8,060 hours as first officer in the MD-80.

FAA and company records showed no accident, incident, or enforcement or disciplinary actions taken against none of the work forces. ( NTSB )

NTSB Probable Cause

The National Transportation Safety Board determines that the likely cause of this accident was a loss of airplane pitch control ensuing from the in-flight failure of the horizontal stabilizer spare system jackscrew assembly ‘s acme nut togss. The thread failure was caused by inordinate wear ensuing from Alaska Airlines ‘ deficient lubrication of the screw jack assembly. Lending to the accident were Alaska Airlines ‘ drawn-out lubrication interval and the Federal Aviation Administration ‘s ( FAA ) blessing of that extension, which increased the likeliness that a lost or unequal lubrication would ensue in inordinate wear of the height nut togss, and Alaska Airlines ‘ drawn-out terminal drama cheque interval and the FAA ‘s blessing of that extension, which allowed the inordinate wear of the height nut togss to come on to failure without the chance for sensing. Besides lending to the accident was the absence on the McDonnell Douglas MD-80 of a fail-safe mechanism to forestall the ruinous effects of entire acme nut thread loss.


The flight crewmembers on Alaska Airlines flight 261 were decently certificated and qualified and had received the preparation and off-duty clip prescribed by Federal ordinances. No grounds indicated any preexisting medical or other status that might hold adversely affected the flight crew ‘s public presentation during the accident flight. The aeroplane was dispatched in conformity with Federal Aviation Administration ordinances and approved Alaska Airlines processs. The weight and balance of the aeroplane were within bounds for despatch, takeoff, ascent, and sail. Weather was non a factor in the accident. No grounds indicated that the aeroplane experienced any pre-impact structural or system failures, other than those associated with the longitudinal trim control system, the horizontal stabilizer, and its surrounding construction. Both engines were runing usually before the concluding honkytonk. Air traffic control forces involved with the accident flight were decently certificated and qualified for their assigned responsibility Stationss. The longitudinal trim control system on the accident aeroplane was working usually during the initial stage of the accident flight. The horizontal stabilizer stopped reacting to autopilot and fly bids after the aeroplane passed through 23,400 pess. The pilots recognized that the longitudinal trim control system was jammed, but neither they nor the Alaska Airlines care forces could find the cause of the jam.

Table of Contentss

Introduction 1

Accident Flight 2-4

Flight Crew 4-5

NSTB Probable Cause 5

Decision 7

Mention 8

Pictures and Diagrams

Longitudinal Trim System Description and Failure Sequence

Gimbal Nut and Jackscrew

Jackscrew from horizontal stabilizer of Alaska Airlines flight 261