Sometimes we take airline safety for granted. But we were just reminded by a video of when United Airlines Flight 811 from Honolulu was torn apart mid-air soon after takeoff. A massive explosive decompression expelled several rows of seats from the plane, and nine passengers were killed whose bodies were never recovered. The flight started in Los Angeles and landed in Honolulu uneventfully, on its regular daily route to Sydney with intermediate stops. Nothing was reported as being amiss by the flight crew.
The event occurred on February 24, 1989, when the Boeing 747-100 cargo door failed shortly after takeoff from HNL. Miraculously, the heavily damaged aircraft was able to return to Honolulu and land safely. The plane was later repaired and returned to service at United. The aircraft had flown nearly 60k flight hours on 15k flights without incident prior to that day.
After the Flight 811 accident, the plane was repaired and returned to service at UAL for another 8 years before going to another airline where it flew until 1998.
The flight that fateful day.
The flight was under the control of Captain David Cronin, and it was to be his last flight before reaching the then-mandatory retirement age. The flight took to the air just before 2 AM in Hawaii, with 355 total passengers and crew onboard. As the flight climbed out of HNL, at 23k feet, a loud noise followed by strong vibration occurred. Firest thought to have been caused by a bomb, the forward cargo door of the plane had actually been ripped off. The design of the door was that swung out, rather than in, and its force tore a large hole in the plane’s fuselage. Then the plane’s cabin floor caved in, and 10 seats were ejected from the 747. Two of those seats were unoccupied, but the remaining seat occupants were killed.
One flight attendant was nearly sucked out of the cabin, as happened on Aloha Airlines Flight 243 when it suffered an explosive decompression just months earlier. Passengers and crew on the UAL 747 came to the flight attendant’s rescue and were able to pull her back inside the plane. She did, however, suffer significant injury.
The flight crew suspected a bomb due to the current events.
It was thought at the time that a bomb may have exploded inside the 747, as had happened to Pan Am’s flight 103 just prior to flight 811.
Emergency descent and preparation for landing.
A rapid descent to achieve breathable air was initiated as the plane turned back to land at Honolulu. Because of the location of the explosion, emergency oxygen was not working.
Two of the four engines and more were damaged in the explosive decompression.
Flying parts of the plane damaged two of the four engines. Both of those had to be shut down as a result. One of the wings was also dented and damaged.
Preparation for emergency landing at HNL.
Preparation was made for an emergency landing back at Honolulu. The intercom system failed which prevented the cockpit and cabin crew from communicating. The flight engineer went down to advise the cabin crew and to try to determine what had happened. He incorrectly believed it had been a bomb exploding that caused the damage.
In spite of the flaps not working fully, the landing gear remained functional, and a high-speed landing was initiated successfully.
14 fateful minutes in time before landing.
It took just 14 minutes from the time of the explosion until its return to HNL. Miraculously, the entire plane was evacuated on landing within under 45 seconds.
Flight attendant heroes don’t have easy jobs.
It was reported that every one of Flight 811’s flight attendants was injured during the incident and the evacuation.
The National Transportation Safety Board (NTSB).
The NTSB couldn’t find the missing cargo door initially, but based on prior issues with cargo doors came to their conclusion. Another 747, that one owned by Pan Am, had a door incident at 20k feet which caused the flight to be aborted The door was found to be open on one edge by 1.5 inches. Investigators found that the locking mechanism was damaged. Boeing initially believed this was caused by ground crew error,
The NTSB first determined that previous malfunctions in the plane’s forward cargo door damaged the door lock. As a result, it appeared to be latched and locked, but it was in fact not. NTSB blamed UAL for improper maintenance and inspection.
Further independent investigation however led some to conclude that in fact, it was a design problem combined with an electrical problem that resulted in the door opening mid-flight. The design of an outward swinging door, which is more cargo-efficient, was also thought to be largely at fault. It was subsequently reported that Boeing knew of a locking problem for almost 14 years. They had recommended changes to the operator airlines including changing from thin aluminum to heavier steel components. That was followed by a related FAA airworthiness directive in July of 1988 which gave airlines up to two years to comply. Following this incident, that was revised to be a 30-day directive.
The cargo door was later recovered at a depth of 14k feet off of Hawaii.
The NTSB inspection found that the locking mechanism theory was incorrect. Based on developments including another UAL 747 incident at JFK, an updated final report was issued in 1992 which stated the probable cause of the incident was a sudden opening of the cargo door due to a combination of improper wiring and cargo door deficiencies. As a result of a short circuit, latching devices operated unexpectedly, which allowed aerodynamics to cause the door to blow off.