United Airlines Flight 811
 CGI image of Flight 811 just after decompression | |
| Occurrence | |
|---|---|
| Date | February 24 1989 |
| Summary | Structural failure |
| Site | Pacific Ocean near Honolulu, Hawaii |
| Aircraft type | Boeing 747-122 |
| Operator | United Airlines |
| Registration | N4713U |
| Flight origin | Los Angeles International Airport |
| Stopover | Honolulu International Airport |
| Last stopover | Auckland Airport |
| Destination | Kingsford Smith International Airport |
| Passengers | 337 |
| Crew | 18 |
| Fatalities | 9 |
| Injuries | 38 |
| Survivors | 346 |
United Airlines Flight 811 experienced a cargo door failure in flight on Friday, February 24, 1989 after its last stopover in Honolulu International Airport, Honolulu, Hawaii, United States. The resulting decompression blew out several rows of seats containing 9 passengers, who were killed.
Incident
United Airlines Flight 811, a Boeing 747-122 (registration number N4713Udisaster[1]), took off from Honolulu International Airport bound for Sydney, Australia, via Auckland, New Zealand with 3 flight crew, 15 flight attendants, and 337 passengers aboard at approximately 01:52 local time.[2] It was under the command of Captain David Cronin.
During the climb, they detected thunderstorms located to the south, ahead of the airplane's course. As a result, Captain Cronin kept the fasten seat-belt light on, and instructed the First Officer to request clearance to 33,000 feet, and to tell the center that they were going to detour over to the left of assigned course. Around this time (02:08) the plane had been flying for approximately 16-minutes and was passing between 22,000 and 23,000 feet. In the business-class section, a grinding noise was heard, followed by a loud thud which rattled the whole aircraft -- 1.5 seconds from that point the R5 cargo-door blew-out abruptly; the pressure differential caved-in the floor above the door, causing five rows of seats, and an individual in row 9F, to be ejected from the cabin resulting in 9 fatalities (A flight-attendant in the Business-Class cabin was also severely injured), and left a gaping hole in the aircraft. The pilots began an emergency descent to get the airplane rapidly down to breathable air, while performing a 180-degree left turn to take them back to Honolulu. All three crew members donned their oxygen masks only to find they weren't working as the damage to the plane happened to destroy the plane's oxygen-supply, so they took them off.
The debris ejected from the plane during the explosive decompression caused severe damage to the number 3 and 4 engines, causing visible fires in both. The crew did not get fire-warnings from either of them, although engine 3, experiencing heavy vibration, no N1-reading, and oddly, low EGT and EPR, and was shut-down. At 02:10 an emergency was declared, and the crew began frantically dumping fuel to get the plane's weight down to an acceptable landing weight. Initially, they pushed the No 4 engine a bit to help force the plane down faster, but once they noticed it was giving almost no N1, high EGT, and noticed flames coming out of it, they shut it down also. Some of the explosively ejected debris damaged the right-wing's LED's (Leading Edge Devices) dented the horizontal stabilizer on that side, and even struck the tailfin.
During the course of the descent, the Flight-Engineer, unable to contact the Flight-Attendants (Captain Cronin told the Flight-Engineer to tell the flight-attendants to prepare for an emergency landing) asked the Captain if he could go down and find out what was happening. Cronin gave told him to check what was going on. Immediately after leaving the cockpit, he already saw severe damage -- skin was peeled off in some areas on the upper deck revealing the frames and stringers; as he went down to the lower deck the full magnitude of the damage became completely obvious as he now saw the gigantic hole in the side of the plane. The F/E came back to the cockpit telling them how essentially a huge section of the fuselage aft of the number 1 exit door was essentially open. He concluded that it was probably a bomb, and considering the condition of the plane, it would be unwise to exceed 250 kts. The plane's stall speed is around 240 kts clean so it was kind of a balancing act.
As the airplane neared the airport, the gear was extended properly although due to the damage to the flaps, they were only able to safely extend 10-degrees. This resulted in a landing speed between 190 kts and 200 kts. Regardless, Captain Cronin was able to get the plane to a halt without going off the end of the runway. 14 minutes had elapsed since the emergency was declared. Evacuation was carried out and all passengers and F/A's were off in less than 45-seconds. Unfortunately every single flight-attendant was injured during the evacuation, ranging from scratches to a dislocated shoulder.
Cause
The accident was most likely caused by improper wiring and deficiencies in the door's design. Unlike a plug-door which opens inwards and essentially jams against its frame as the pressure outside drops, the B-747 uses an outward hinging door which, while increasing capacity, requires a locking-mechanism to keep the door closed: The Boeing 747's cargo-door utilized a series of electrically-operated latch cams which the latch pin locks in with, the cam then rotating into the closed-position. A series of L-shaped arms called locking-sectors, actuated by the moving of a lever to close the door are designed to reinforce the latch-cams and prevent them from rotating into the un-locked position. The locking-sectors were made out of aluminum, and of too thin a gauge to actually be able to keep the latch-cams from moving into the un-locked position. The S-2 Master Lock switch which was designed to cut electrical power to the doors when the outer-handle closed was faulty and could operate in flight. It would appear in this case that a short-circuit in the aging plane caused an uncoomaned rotation of the latch-cams, which forced the weak locking-sectors open during the opening sequence. The pressure-differential and aerodynamic forces did the rest.
The aircraft was approximately 60 miles from Honolulu and between 22,000 and 23,000 feet, leaving the passenger cabin exposed to the elements. It managed to make a safe turnaround and a safe landing, after which an evacuation was immediately carried out.
Personal investigation
Lee Campbell was one of the casualties on flight 811. He was a New Zealander returning home to New Zealand. After his death, Lee Campbell's parents Kevin and Susan personally pursued an investigation to find out what really went wrong with the plane's engineering. Their investigation led them to conclude that the design of the aircraft's cargo door latching mechanism had been flawed.[3]
-As early as 1975, Boeing realized the aluminum locking-sectors were of too thin a gauge to be effective and recommended the airlines add doublers to the locking sectors. It turned out that most of the airlines did not actually make the modifications and to make it worse, they were not sturdy enough even then.
-In 1987 a Pan American flight departing London Heathrow Airport encountered pressurization problems at 20,000 feet. After conducting a descent, the problem subsided at approximately 15,000 feet with the crew attempting to climb again. As the plane passed through 20,000 feet for the second time, the problems resurfaced again. The crew returned to Heathrow, landing safely. However the cargo-door was hanging open by about an 1.5 inches at the bottom with all the latch-cams open. When the plane was taken back to the maintenance base, it was discovered all the locking-sectors were either bent or broken. Boeing initially attributed this to mishandling by ground crew, however worries about the electrical system popped up. As a result, Boeing instructed the airlines to conduct a simple test: Close the outer handle, then press the switch to open the door. Unexpectedly, it actually worked.
-Boeing issued a directive ordering customers to replace the aluminum locking-sectors with steel locking-sectors, and carry out various inspections. The FAA gave the airlines 18-months to comply with the directive. After flight 811, the FAA shortened the time to 30-days.
-In 1991, an incident occurred at New York's JFK airport involving the malfunction of a United Airlines Boeing 747 cargo door.[4] At the time, United Airlines' maintenance staff were investigating the cause of a circuit breaker trip. In the process of diagnosing the cause, an inadvertent operation of the electric door latch mechanism caused the cargo door to open spontaneously. This incident led to latch damage similar to that observed on the flight 811 cargo door.
Needless to say, the Campbells' investigation and hypothesis subsequently gained more credibility.
-Two pieces of the flight 811 cargo door were recovered from the Pacific Ocean on 26 September 1990 and 1 October 1990.
Result
The NTSB issued an emergency recommendation for all 747-100s in service at the time to replace their cargo door latching mechanisms with new, non-faulty locks.[5] A subrecommendation suggested replacing all outward-opening doors with inward-opening doors, which cannot open in flight due to the pressure differential. No similar accidents have occurred on 747-100s since this accident.
In 1989, the flight crew received the Secretary's Award for Heroism for their actions.[6] The aircraft was successfully repaired, re-registered as N4724U, and returned to service in 1990.
United Airlines ran a simulation through a flight simulator and were, despite many attempts and variable tweaks, unable to successfully land a plane after losing the R5 door.[citation needed]
See also
- Turkish Airlines Flight 981 - cargo door failure.
- American Airlines Flight 96 - cargo door failure.
- Pan Am Flight 125 - cargo door failure.
- Aloha Airlines Flight 243 - another decompression.
- British Airways Flight 5390 - another decompression.
- de Havilland Comet — explosive decompression
References
- ^ "FAA Registry (N4713U)". Federal Aviation Administration.
- ^ AAR92-02 NTSB report
- ^ Mayday Air Disaster Documentary: Unlocking Disaster
- ^ NTSB Safety Recommendation A91-84 & 84, 28 August 1991
- ^ Aircraft Accident Report Number AAR-92/02 Executive Summary, National Transportation Safety Board.
- ^ Honoring the Crew of United Airlines Flight 811, House of Representatives, Page H1798, May 10, 1989, Retrieved from the Library of Congress.