United Airlines Flight 811

United Airlines Flight 811 was a regularly scheduled international flight from Los Angeles to Sydney, with intermediate stops at Honolulu and Auckland. On February 24, 1989, the Boeing 747 serving the flight experienced a cargo-door failure in flight shortly after leaving Honolulu. The resulting explosive decompression blew out several rows of seats, killing nine passengers. The aircraft returned to Honolulu and landed without further incident.

In its report on the accident in April 1990, the NTSB asserted that it was not possible for a properly latched cargo door to have opened in mid-flight, and focused primarily on potential mishandling of the door by ground crew. It blamed the accident on in-service damage to the door locking mechanism. An alternative investigation by the parents of one of the victims focused instead on the design of the door latching mechanism and the electrical system that opens it. After the final report on the incident was issued, the cargo door was recovered by a deep-sea operation, and its condition was not consistent with the report. After another incident occurred on a 747 aircraft undergoing maintenance in 1991, the NTSB issued a superseding final report in March 1992 that attributed the accident to the electrical system malfunctioning and causing the door to open during flight, along with deficiencies in the door's latching design, as had been suggested by the independent family investigation.

Aircraft

thumb|left|The aircraft in the accident, seen in 1993 after being repaired and re-registered as N4724U

The aircraft involved was a Boeing 747-122 (registration number N4713U). Its serial number was 19875 and it was the 89th 747 built. At the time of the accident, the aircraft had accumulated 58,814 total flight hours and 15,028 flight pressurization cycles, and had not been involved in any previous accidents.

Flight crew

Starting in Honolulu, Flight 811 was under Captain David M. Cronin (age 59).

The remaining flight crew consisted of First Officer Gregory Allen "Al" Slader (48), and Flight Engineer Randal Mark Thomas (46), and 15 flight attendants.

!Nationality

!Fatalities

Flight 811 took off from Honolulu International Airport at 01:52 local time, with 337 passengers and 18 crew members on board. All eight passengers occupying these seats were ejected from the aircraft, as was the passenger in seat 9F. Seats 8G and 12G were unoccupied.

File:Faa.gov flight 811 UnitedHawaii.gif|The massive hole in the fuselage

File:United Airlines Flight 811（N4713U） damage.jpg|Nine passengers were ejected through this hole in the fuselage

File:Faa.gov flight 811 after landing.jpg|Damage visible after landing

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Investigation

NTSB initial investigation

thumb|Flight 811 after landing

thumb|A view of the engines from the hole in the fuselage

The National Transportation Safety Board (NTSB) immediately commenced an investigation into the accident. An extensive aerial and surface search of the ocean had initially failed to locate the aircraft's cargo door. The NTSB proceeded with its investigation, without the cargo door to inspect, issuing a final report on April 16, 1990. After that aircraft landed safely back at London Heathrow Airport, the aircraft's cargo door was found to be ajar by about along its ventral edge. When the aircraft was examined further, all of the door's locking arms were found to be either damaged or entirely sheared off. Boeing initially attributed this to mishandling by ground crew. To test this theory, Boeing instructed 747 operators to shut and lock the cargo door with the external handle and then activate the door-open switch with the handle still in the locked position. Nothing should have happened since the S-2 switch was designed to deactivate the door motors if the handle was locked. Some airlines reported that the door motors did indeed begin running; however, they attempted to force the door open against the locking sectors and caused damage to the mechanism.

The Boeing 747 was designed with an outward-hinging cargo door, unlike a plug door, which opens inward and jams against its frame when closed as the pressure drops outside in flight, making accidental opening at high altitude impossible. The outward-swinging door increases the aircraft's available cargo capacity (less room inside the fuselage must be kept clear to accommodate the door's range of motion) but requires a strong locking mechanism to keep it closed. Deficiencies in the design of wide-body aircraft cargo doors have been known since the early 1970s due to flaws in the DC-10 cargo door. These problems were not fully addressed by the aircraft industry or the FAA, despite the warnings and deaths from the DC-10's cargo door-related accidents.

The 747's cargo door used a series of electrically operated latch cams into which the door-edge latch pins closed. The cams then rotated into a closed position, holding the door closed. A series of L-shaped arms (called locking sectors) were actuated by the final manual movement of a lever to close the door; these were designed to reinforce the unpowered latch cams and prevent them from rotating into an unlocked position. The locking sectors were made out of aluminum, however, and they were too thin to keep the latch cams from moving into the unlocked position against the power of the door motors. Electrical switches cut electrical power to the cargo door when the outer handle was closed; if one was faulty, the motors could still draw power and rotate the latch cam to the open position. The same event could happen if frayed wires could power the cam motor, even if the safety switch cut the circuit power. The NTSB inspected the cargo door and determined that the condition of the locking mechanism did not support its original conclusions. At the time, United Airlines' maintenance staff was investigating the cause of a circuit-breaker trip. In diagnosing the cause, an inadvertent operation of the electric door latch mechanism caused the cargo door to open spontaneously despite being closed. An inspection of the door's electrical wiring discovered insulation breaches, and isolating certain electrical wires allowed the door to operate normally again.

In popular culture

The fatal event on United Airlines Flight 811 was featured on three episodes of the Canadian-made, internationally distributed documentary series Mayday: "Unlocking Disaster" (the 2003 series premiere), "Terror Over The Pacific" (2024), and as one of the six incidents addressed in the 2007 special episode "Ripped Apart".

The incident is featured in the bestselling book The Checklist Manifesto by Atul Gawande.

The incident is also featured in Why Planes Crash in the episode "Breaking Point".

References

External links

First NTSB Aircraft Accident Report AAR-90/01 (superseded by Report AAR-92/02)
Second NTSB Aircraft Accident Report AAR-92/02—Copy at Embry–Riddle Aeronautical University
Transcript of cockpit voice recorder
Pre-accident photos of N4713U