United Airlines Flight 811

United Airlines Flight 811 was a regularly scheduled airline flight from Los Angeles to Sydney, with intermediate stops at Honolulu and Auckland. On February 24, 1989, the Boeing 747-122 serving the flight experienced a cargo door failure in flight shortly after leaving Honolulu. The resulting explosive decompression blew out several rows of seats, resulting in the deaths of nine passengers. The aircraft returned to Honolulu, where it landed without further loss of life.

The aircraft involved was a Boeing 747-122 (registration number N4713U). It was delivered to United Airlines on November 3, 1970. At the time of the accident, the Boeing had accumulated 58,814 total flight hours, 15,028 flight 'pressurization' cycles, and had not been involved in any previous accident.

Aircraft
N4713U, photographed in 1982 at Los Angeles, seven years before the accident. The same aircraft in service with Air Dabia, photographed in 1999 at Miami Airport, 10 years after the incident

The aircraft involved was a Boeing 747-122 (registration number N4713U). It was delivered to United Airlines on November 3, 1970. At the time of the accident, the Boeing had accumulated 58,814 total flight hours, 15,028 flight 'pressurization' cycles, and had not been involved in any previous accident.

On February 24, 1989, the aircraft was scheduled by United Airlines to operate as Flight 811 from Los Angeles International Airport in Los Angeles, California to Sydney Airport in Mascot, New South Wales, Australia, with intermediate stops at Honolulu International Airport in Honolulu, Hawaii and Auckland Airport in Auckland, New Zealand. Flight 811 operated without incident on the first leg of its scheduled flight, from Los Angeles to Honolulu, and there were no difficulties reported by the flight crew upon arriving at Honolulu, where a crew change occurred.

After the accident, the aircraft was repaired and put back into service with United, but was re-registered N4724U. In 1997, the aircraft was taken out of service and passed onto Air Dabia as C5-FBS. Air Dabia ceased operations in 1998, and the aircraft was abandoned at Plattsburgh International Airport, where it was scrapped in 2004.

Flight crew
Starting in Honolulu, Flight 811 was helmed by Captain David Cronin, age 59. At the time of the accident, Cronin had logged around 28,000 flight hours, including approximately 1,600 to 1,700 hours in Boeing 747 aircraft. Flight 811 was Cronin's penultimate scheduled flight before his mandatory retirement.

The remaining flight crew consisted of First Officer Gregory Slader, age 48, and Flight Engineer Randal Thomas, age 46, and fifteen flight attendants. The first officer and flight engineer had logged 14,500 flight hours and 20,000 flight hours, respectively.

Accident
Flight 811 took off from Honolulu International Airport at 01:52 local time, with 337 passengers and 18 crew members on board.

During the climb, the crew made preparations to detour around thunderstorms along the plane's track; the captain anticipated turbulence and kept the passenger seatbelt sign lit. The aircraft had been flying for 17 minutes, as it was passing from 22,000 to 23,000 feet (6,700 to 7,000 m), when the flight crew heard a loud "thump" which shook it. About a second and a half later, the forward cargo door blew off. It swung out with such force that it passed its normal stop and slammed into the side of the fuselage, bursting it open. Pressure differentials and aerodynamic forces caused the cabin floor to cave in, and ten seats (G and H of rows 8 through 12) were ejected from the cabin. All eight passengers seated in these locations were killed, as was the passenger in seat 9F. Seats 8G and 12G were unoccupied. A gaping hole was left in the aircraft, through which a flight attendant, Mae Sapolu, in the business-class cabin was almost blown out. Senior flight attendant Laura Brentlinger hung on to the steps leading to the upper deck, and was dangling from them when the decompression occurred. Passengers and crew members saw her clinging to a seat leg and were able to pull her back inside the cabin, although she was severely injured.

The pilots initially believed that a bomb had gone off inside the airliner, as this accident happened just two months after Pan Am Flight 103 was blown up over Lockerbie, Scotland. They began an emergency descent in order to reach an altitude where the air was breathable, while also performing a 180-degree left turn to fly back to Honolulu. The explosion damaged components of the on-board emergency oxygen supply system, as it was primarily located in the forward cargo sidewall area, just aft of the cargo door.

The debris ejected from the aircraft during the explosive decompression damaged the Number 3 and 4 engines Engine 3 was experiencing heavy vibration, no N1 tachometer reading, and a low exhaust gas temperature (EGT) and engine pressure ratio (EPR), so the crew shut it down. At 02:20, an emergency was declared and the crew began dumping fuel to reduce the aircraft landing weight. The N1 reading of engine number 4 soon fell to almost zero, its EGT reading was high, and it was emitting flames, so they shut it down as well. Some of the explosively ejected debris damaged the right wing's leading edge, dented the horizontal stabilizer on that side, and damaged the vertical stabilizer.

During the descent, Captain Cronin ordered Flight Engineer Thomas to tell the flight attendants to prepare for an emergency landing, but he was unable to contact them through the intercom. He asked the captain for permission to go down to find out what was happening, and he agreed. Thomas saw severe damage immediately upon leaving the cockpit; the aircraft 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 magnitude of the damage became apparent as he saw the large hole in the side of the cabin. He returned to the cockpit and reported that a large section of the fuselage was open aft of the Number 1 exit door. He concluded that it was probably a bomb and that, considering the damage, it would be unwise to exceed the plane's stall speed by more than a small margin.

As the airliner neared the airport, the landing gear was extended. The flaps could only be partially deployed as a result of damage sustained following the decompression. This necessitated a higher than normal landing speed of around 190–200 knots (350–370 km/h; 220–230 mph). Captain Cronin was able to bring the aircraft to a halt without overrunning the runway. 14 minutes had elapsed since the emergency was declared. All the remaining passengers and flight attendants exited the aircraft in less than 45 seconds. Every flight attendant suffered some injury during the evacuation, ranging from scratches to a dislocated shoulder.

Despite extensive air and sea searches, no remains of the nine victims lost in flight were found at sea. Multiple small body fragments and pieces of clothing were found in the Number 3 engine, indicating that at least one victim ejected from the fuselage was ingested by the engine, but it was not known whether the fragments were from one or more victims.