Aviation isn’t always the safest mode of transport in the world. Fatal accidents occur despite the attempts. However, each incident teaches the air transport sector on measures to improve air safety. One such air incident is of United Airlines Flight 811. It was a flight with a regular schedule between Los Angeles and Sydney, having Honolulu and Auckland as its intermediate points. Boeing 747-122 flight UA 811 encountered failure in cargo door while in flight after leaving Honolulu. The subsequent explosive compression led to the fatality of 9 passengers as several sear rows were blown out due to decompression. To save further lives of passengers, the captain returned Boeing 747 back to Honolulu Airport, where it had shortly left.
What actually happened?
Sheer negligence and lack of careful attention can cost aircraft crashes, especially if the aircraft maintenance and well-being are compromised. United Airlines comes foremost in such a case. UA 811, meant to be just another regular commercial flight for passengers on February 24, 1989, with origin point of Los Angeles and Sydney as the destination with intermediate stopovers at Honolulu Airport and Auckland Airport, commenced its flight at 1:33 am local flight. The first leg of this flight (i.e., from Los Angeles to Honolulu) didn’t encounter any incident and operated as usual.
Upon arrival at the first stopover airport of Honolulu, the crew changed, and the flight continued its journey, leaving Honolulu, carrying a total of 355 people on board, with 337 passengers and 18 crew members. Flying in the air for 17minutes with an elevation from 22000 to 23000 feet, the aircraft was still climbing out of Hawaii; the loud ‘thud’ was heard, which shook the aircraft. The cargo door of the front part blew off, the fuselage burst open as the door slammed into the side of it, and nine passengers were sucked into nowhere.
Ten seats (rows 8 through 12 G and H seats) were ejected. The passenger seated in 9F was also killed. There were no passengers sitting on 8G and 12G. Since the forward cargo door had been swung wide, the aircraft was left with a massive gaping hole that almost blew out the flight attendant named Mae Sapolu. She was in the business class cabin when it happened. The senior flight attendant Laura Bretingle was dangling from the steps of the spiral staircase of the aircraft, which led to the upper deck when the decompression occurred.
She was seriously injured but was pulled back by the passengers and crew members when she was clinging to her seat leg. The decompression explosion had already snuck out nine passengers; only 328 passengers remained. Most of the victim’s seats were ejected out along with victims due to differences in pressure and aerodynamic forces inside and outside the aircraft because the cargo door had been ripped off. During the climbing out of Hawaii, the captain of flight 811 anticipated turbulence and lit the passenger seatbelt. The cabins inside the aircraft are kept pressurized so that people can respire. Once aircraft has a hole, it causes the pressurized air to rush out. The explosive decompression burst out about a second and a half later the crew had heard a thud.
Captain David Cronin, First officer Gregory Slader, Flight engineer Randal Thomas of United Airlines 811 led the aircraft back to Honolulu. The pilots donned their oxygen masks, but no oxygen was available. Since it was kept at the aft of the cargo door, it had been damaged by the explosion in the front cargo sidewall area. The air was filled with flying debris and foggy smoke. The captain quickly started emergency descent. The first officer communicated with ATC through the radio about the emergency descent to get the aircraft down to a lower altitude where there was breathable air while performing 180 degrees left turn away from the storm.
The flying debris and decompression caused trouble to the number 3 engine that the captain noticed during the descent. To find out the reason for the vibration of the aircraft and the plummet of exhaust temperature, the second officer saw that the forward fuselage was missing on the right-hand section.
Flight crew members were struggling through strong winds. The engine number 4 also didn’t work. Sparks of flames could be seen from the engine. So, the engines were shut down. Captain David Cronin had the habit of practicing for different emergency situations; his hand flew to cruising altitude. So it was conducive not to let the situation worsen further.
The captain made the emergency landing back at Honolulu airport. Landing gear extended near to the airport. The captain was able to land in 24 minutes after the cargo door was blown off the fuselage. As flaps were extended, and only a partial portion of them could be deployed due to damage, the extension was asymmetrical. But using the trailing edge flaps on the right-wing, the aircraft was brought to a halt.
They landed on runway 8L at Honolulu without overrunning it. So, with two of the engines out and flaps not in working condition; however, the aircraft touched down on the runway along with a huge gaping hole on the side. At 2:34 am local time, the plane stopped on the runway, and without any further delay, the evacuation took place right there on the runway. All the passengers and cabin attendants did not take a minute to get off the aircraft. The evacuation caused some injury to the flight attendants. Some had just a scratch, while others had dislocated arms.
The nine people who fell apart from the sky were not found. The search team couldn’t find them despite extensive air and sea search.
Description of the aircraft
Boeing 747 had released its initial version of the 747-100 series to be operated by 3 flight crew with a seating capacity of 366-452 passengers. With a length of 231 feet 10.2 inches, a height of 63 feet 5 inches, inter cabin width of 20 feet, and a wingspan of 20 feet, it was named ‘wide-body.’ It has a maximum takeoff weight of 735000 pounds and an empty weight of 370816 pounds. It was twice as big as other versions of Boeing, with four engines, main deck cabin possessing two aisles, which could fly in commercial services. It was the revolutionary aircraft and first wide-body jet. At the time accident happened, this Boeing jet had completed 15028 flights, a total of 58814 flight hours, and hadn’t experienced any past accident yet.
National Transportation Safety Board (NTSB) investigated the accident quickly. It issued its report in April 1990 with the assumption that the malfunctions of the forward cargo door had damaged the locking mechanism in a manner that the door showed lock and latched position though it wasn’t. The cargo door that had been missing wasn’t found yet despite the air and sea search. It was concluded that the cause of the accident was human error.
Based on this assumption, NTSB also blamed United Airlines for not inspecting properly as the faulty locking mechanism wasn’t identified. NTSB report didn’t find any problem in the cargo door design or function. NTSB read prior accidents regarding cargo doors and circumstantial evidence. About six months after the conclusion of NTSB, two halves of the cargo door were located on the Pacific ocean,14000 feet below the surface on September 26 and October 1, 1990. Inspection of cargo doors clarified that the condition of the locking mechanism didn’t match the conclusion of NTSB.
The probable cause behind the incident
The forward cargo door suddenly opened, and explosive decompression occurred subsequently. Series of electrically operated latch cams were used in Boeing 747’s cargo door. The door edge latch pins were closed into it. As the locking mechanism was thin, made out of aluminum, they couldn’t stop the latch cams’ movement into an unlocked position against the door motor’s power. Boeing recommended the airlines equip locking sectors with doublers. Following the 1987 Pan Am B-747 cargo door opening incident, Boeing issued the notice to inspect and use steel locking sectors instead of aluminum.
In 1991, United Airlines Boeing 747 again had a malfunction of the cargo door at John F. Kennedy International Airport. No signs of damages were shown on the lock, latch pins, and latch cams. NTSB later released the superseding accident report on March 8, 1992, where it demonstrated that the cargo door opening was attributed to improper wiring and faulty deficiencies on the door control system. The short circuit caused an uncommon rotation of cargo door latch cams. The defective switch allowed the electrical actuation of door latches, enabling the pressure differential and aerodynamic force.
The locking mechanism of cargos wasn’t designed enough to be unsusceptible to deformation. Boeing couldn’t take the corrective action on time. The NTSB recommended Boeing 747’s to place the newly designed locks on cargo doors. A sub recommendation was also made to place doors opened from inside and can’t open in flights because of differences in air pressure. Since then, no such accidents have occurred on 747’s which have cost human lives.
In 1989, Secretary Award was presented to the flight crew of 811 for their heroic action. The aircraft came back in service in 1990 after being repaired and getting N4724U registration in 1989. The spare parts of the aircraft were scrapped out in 2004.