Thursday 24 February 2022

Remembering United Airlines Flight 811

UNTITED B0EING 747-422 N194UA (MSN 26892)

United Airlines Flight 811 was a regularly scheduled airline flight from Los Angeles to Sydney, with stop overs at Honolulu and Auckland. On the 24th February 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 and landed with no further incident.

Flight 811, with 337 passengers and 18 crew members on board, took off from Honolulu (HNL/PHNL), Hawaii at 01:33 local time, bound for Sydney, Australia (SYD/YSSY), with an intermediate stop at Auckland, New Zealand (AKL/NZAA). The initial climb passed through an area of thunderstorms, so the captain elected to keep the seat belt sign on. As the aircraft was climbing, between 22,000 and 23,000 feet, an explosive decompression was experienced. An emergency was declared at approximately 02:20 HST. The captain initiated a 180-degree left turn to avoid a thunderstorm and proceeded toward Honolulu. The forward lower lobe cargo door had opened in flight, taking with it a large portion of the forward right side of the cabin fuselage. The starboard side Pratt & Whitney JT9D-7A engines (no.3 and 4) were damaged and had to be shut down. Parts of the leading and trailing edge flaps where also damaged resulting in the crew electing to use only 10-degrees trailing edge flaps for landing (a non-normal configuration). This resulted in the aircraft having to land at a higher speed than it would under normal conditions. The aircraft was cleared to land on Honolulu's runway 8L. At 02:34 HST, Honolulu tower was notified by the flight crew that the airplane was stopped and an emergency evacuation had commenced on the runway. 

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 10 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 aircraft involved was a Boeing 747-122 (registration number N4713U MSN 19875).
It was delivered to United Airlines on the 3rd November 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.

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