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.

Flight crew

Starting in Honolulu, Flight 811 was under Captain David M. Cronin (age 59). At the time of the accident, Cronin had logged around 28,000 flight hours, including roughly 1,600 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 Allen "Al" Slader (48), and Flight Engineer Randal Mark Thomas (46), and 15 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 22000 to 23000 feet, the flight crew heard a loud "thump", which shook the plane. About a second and a half later, the forward cargo door separated from the aircraft. It swung out with such force that it tore a massive hole in the fuselage. This caused the plane to slightly bank to the left. Pressure differentials and aerodynamic forces caused the cabin floor to cave in, and 10 seats (G and H of rows 8 through 12) were ejected from the cabin. All eight passengers occupying these seats were ejected from the aircraft, 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. Purser 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 to reach an altitude where the air was breathable while also performing a 180° 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, so the crew shut it down. At 02:20, an emergency was declared, and the crew began dumping fuel to reduce the aircraft's 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 the pilots 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 Thomas could not contact them through the intercom. Thomas asked the captain for permission to go down to find out what was happening, and Cronin 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 Thomas 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. Thomas returned to the cockpit and reported that a large section of the fuselage was open aft of the Number 1 exit door. Thomas concluded that it was probably a bomb.

As the airliner neared the airport, the landing gear was extended, but the flaps could only be partially deployed as a result of damage sustained following the decompression. This necessitated a higher-than-normal landing speed around 190 - 200 kn. Despite these factors, Captain Cronin was able to bring the aircraft to a halt without overrunning the runway. About 14 minutes had elapsed since the emergency was declared. All the remaining passengers and flight attendants evacuated 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. 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 whether the fragments were from one or more victims was not known.