Turkish Airlines Flight 981
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 CG render of TC-JAV moments after failure seen from the cargo door.
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| Summary | |
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| Date | March 3, 1974 |
| Type | Cargo door failure, control failure |
| Site | Ermenonville, France |
| Passengers | 333 |
| Crew | 13 |
| Injuries | 0 |
| Fatalities | 346 |
| Survivors | 0 |
| Aircraft type | McDonnell Douglas DC-10-10 |
| Aircraft name | Ankara |
| Operator | Turkish Airlines |
| Tail number | TC-JAV |
| Flight origin | Yesilköy International Airport |
| Last stopover | Orly Airport (Paris) |
| Destination | London Heathrow Airport |
Turkish Airlines Flight 981,\Tango Hotel Yankee 981 registration TC-JAV, was a McDonnell Douglas DC-10 which crashed just outside Senlis, France, on March 3, 1974. Known as the Ermenonville air disaster after the forest where the aircraft crashed, the accident resulted in the deaths of all 346 on board. The crash of Flight 981 was the deadliest air disaster of all time before the Tenerife Disaster event of 1977, and remained the deadliest single-airliner disaster until the crash of Japan Airlines Flight 123 in 1985.
The crash resulted from the failure of the rear cargo door latching system, which allowed the door to blow off in flight. The resulting decompression of the hold caused the cabin floor above the door to collapse. The control cables for the aircraft that ran through the floor were severed, leaving the pilots with almost no control over the aircraft. Problems with the latching system and the potential failure mode that led to the crash were known to Convair, the fuselage's builder, several years prior to the accident. Changes that addressed the problem had been found, but were not applied to TC-JAV, nor many other aircraft in the DC-10-10 fleet. McDonnell Douglas' reputation, and the reputation of the DC-10, was irreparably harmed.
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[edit] The accident
Flight 981 had flown from Istanbul that morning, landing at Paris's Orly International Airport just after 11:00 am local time. The aircraft, a McDonnell Douglas DC-10, was carrying just 167 passengers and 13 crew members in its first leg. 50 passengers disembarked at Paris. The flight's second leg, from Paris to London's Heathrow Airport, was normally underbooked, but owing to a strike by British European Airways (BEA) employees, many London-bound travelers who had been stranded at Orly were booked onto Flight 981. Among them were 17 English rugby players who had attended a France-England match the previous day; the flight also carried four British fashion models, 48 Japanese bank management trainees on their way to England, as well as passengers from a dozen other countries.
The aircraft departed Orly at around 12:30 pm for its flight to Heathrow. It took off in an easterly direction, then turned to the north to avoid flying directly over Paris. Shortly thereafter the flight was cleared to flight level 230, and started turning to the west for London. Just after Flight 981 passed over the town of Meaux, controllers picked up a distorted transmission from Flight 981; the aircraft's pressurization and overspeed warnings were heard over the pilots' words in Turkish, including the co-pilot saying "the fuselage has burst."
The flight disappeared from radar shortly afterwards and its wreckage was later found at the Grove of Dammartin in the Ermenonville forest, close to the town of Senlis. The aircraft had broken into many small pieces. The post-crash fires were small as there were few large pieces of the aircraft left intact to burn. Of the 346 onboard, only 40 bodies were visually identifiable. Nine passengers were never identified.
The wreckage had been so extensively broken up that immediate investigation suggested that a bomb had been placed on-board. Turkish news reports suggested that a group had intended to bomb a BEA aircraft but had switched planes along with the other passengers. Two terrorist groups soon called to claim responsibility.[1]
[edit] The investigation
Investigators were able to retrieve both the flight data recorder and cockpit voice recorder. These showed that the first hint the flight crew had of any problem was a muffled explosion that took place just after the aircraft passed over Meaux. The explosion was followed by a loud rush of air, and the throttle for the tail-mounted No. 2 engine snapped shut at the same moment. At some point, one of the crew pressed his microphone button, broadcasting the pandemonium in the cockpit on the departure frequency.
The aircraft quickly attained a 20 degree nose-down attitude and started picking up speed while Captain Nejat Berköz and First Officer Oral Ulusman struggled to gain control. As the speed increased the additional lift started to raise the nose again, and Berköz called "Speed!" and started to push the throttles forward again in order to level off. It was too late, however, and 72 seconds after decompression the aircraft slammed into the forest at a speed of 430 knots in a slight left turn. It was the great speed of impact that caused the aircraft to disintegrate.
The wreckage was so fragmented that it was difficult to tell whether any parts of the aircraft were missing. However, an air traffic controller noted that as the flight was cleared to FL230 he had briefly seen a second echo on his radar, remaining stationary behind the aircraft.[2] A farmer soon called and it was discovered that the rear underfloor cargo hold door, portions of the interior floor, and six passenger seats (still holding passengers) had landed in a turnip field near the town of Saint-Pathus, approximately 15 kilometres south of the main crash site.
French investigators determined that the rear underfloor cargo hold door had failed in mid-flight. When it failed, the cargo area decompressed, but not the passenger area above it. The difference in pressure, several pounds per square inch, caused the floor to fail, blowing a section of the passenger cabin immediately above the door out of the open hatch. The control cables, which were routed under the floor, were severed and the pilots lost control of the elevators, the rudder and the No. 2 engine. Without these controls it is almost impossible to control the aircraft.
[edit] The cause
Passenger doors on the DC-10 are of the plug variety, which prevents the doors from opening while the aircraft is pressurized. The cargo door, however, is not. Due to its large area, the cargo door on the DC-10 could not be swung inside the fuselage without taking up a considerable amount of valuable cargo space. Instead, the door swung outward, allowing cargo to be stored directly behind it. The outward-opening door, in theory, allowed it to be "blown open" by the pressure inside the cargo area. To prevent this, the DC-10 used a fail safe latching system held in place by "over top dead center latches", five C-shaped latches mounted on a common torque shaft that are rotated over latching pins ("spools") fixed to the aircraft fuselage. Due to their shape, when the latches are in the proper position, pressure on the door does not place torque on them that could cause them to open, and actually further seats them on the pins.
To ensure this rotation was complete and the latches were in the proper position, the DC-10 cargo door design included a separate locking mechanism consisting of small locking pins slid through holes on the back of the latches. When the locking pins were in place, any rotation of the latches would jam the pins against the fuselage, making further rotation impossible. The pins were pushed into place by an operating handle on the outside of the door; if the latches were not properly closed the pins could not enter the holes and the handle would remain open, visually indicating a problem. Additionally, the handle moved a metal plug into a vent cut in the outer door panel; if the vent was not plugged the door would not retain pressure, eliminating any force on the door. Lastly, there was an indicator light in the cockpit that would remain on if the door was not correctly latched.
In 1972, American Airlines Flight 96, another DC-10, had its cargo door blow off in flight. In the ensuing investigation it was discovered that the handlers had managed to force the locking handle closed in spite of the fact that the latches had not rotated completely due to an electrical problem. Investigators discovered that the rod connecting the pins to the handle was weak enough that it could be bent with repeated operation and some force being applied, allowing the baggage handler to close the handle with his knee in spite of the pins remaining out of their locking holes. Both the vent plug and cockpit light were operated by the handle or the locking pins, not the latches, so when the handle was stowed both of these warning systems indicated that the door was properly closed. In Flight 96's case, the aircraft was able to make a safe emergency landing.
In the aftermath of the Flight 96 incident, the NTSB made several recommendations. Their primary concern was the addition of venting in the rear cabin floor that would ensure that a cargo area decompression would equalize the cabin area and not place loads on the floor. In fact, most of the DC-10 fuselage had vents like these, it was only the rearmost hold that lacked them. Additionally, the NTSB suggested that upgrades to the locking mechanism and to the latching actuator electrical system be made compulsory. However, while the FAA agreed that the locking and electrical systems be upgraded, they also agreed with McDonnell Douglas that the additional venting would be too expensive to implement, and did not demand that this change be made.
Although TC-JAV had been ordered three months after the service bulletin was issued and had been delivered to Turkish Airlines three months later, the changes required by the service bulletin had never been implemented and the interconnecting linkage between the lock and the latch hooks had not been upgraded. Through fraud or oversight, the construction logs nevertheless showed that this work had been carried out. Mohammed Mahmoudi, the baggage handler that closed the door on Flight 981, noted that no particular amount of force was needed to close the locking handle. Investigators concluded that the system had already been fatigued on a prior flight.
Another change implemented after the AA 96 incident was the addition of a small window that allowed the baggage handlers to visually inspect the pins directly, and placards were added to inform them of proper operation. This modification had been carried out on TC-JAV. However, Mahmoudi had not been advised of the meaning or importance of the indicator window. He had been told that as long as the door latch handle stowed correctly and the vent flap closed at the same time, the door was safe. Moreover, the instructions regarding the indicator window were posted on the aircraft in Turkish and English, but the Algerian-born Mahmoudi could not read either language.
It was normally the duty of either the aircraft's flight engineer or Turkish Airlines' chief ground engineer to ensure that all cargo and passenger doors were securely closed before takeoff. In this case, the airline did not have a ground engineer on duty at the time of the accident, and the flight engineer for Flight 981 failed to check the door personally. Although French media called for Mahmoudi to be arrested, investigators stated that it was unrealistic to expect an untrained, low-paid baggage handler who could not read the warning sticker (due to language differences) to be responsible for the safety of the aircraft.
[edit] Aftermath
The latch of the DC-10 is a study in human factors, interface design and engineering responsibility. The control cables for the rear control surfaces of the DC-10 are routed under the floor, so a failure of the hatch could lead to the collapse of the floor, and disruption of the controls. To make matters worse, Douglas chose a new latch design to close it. If the hatch were to fail for any reason, there was a very high probability the plane would be lost. This possibility was first discovered in 1969 and actually occurred in 1970 in a ground test. Nevertheless, nothing was done to change the design, presumably because the cost for any such changes would have been borne out-of-pocket by the fuselage's main contractor, Convair. Dan Applegate was Director of Product Engineering at Convair at the time. His serious reservations about the integrity of the DC-10's cargo latching mechanism are considered a classic case in engineering ethics.
After Flight 981, a complete re-design of the latching system was finally implemented. The latches themselves were re-designed to prevent them from moving into the wrong positions in the first place. The locking system was mechanically upgraded to prevent the handle from being able to be forced closed without the pins in place, and the vent door operation was changed to be operated by the pins, so that it would properly indicate that the pins were in the locked position, not that the handle was. Additionally, the FAA ordered further changes to all aircraft with outward-opening doors, including the DC-10, Lockheed L-1011 and Boeing 747, requiring that vents be cut into the cabin floor to allow pressures to equalize in the event of a blown door.
[edit] Similar accidents
Outward-opening cargo doors are inherently not fail-safe. While an inward opening door (a plug door) which is unlatched will not open due to the difference in pressure between the aircraft cabin and the air outside, an outward opening, non-plug type door needs to be locked shut to prevent unwanted opening. This makes it particularly important that the locking mechanisms be secure. Aircraft types other than the DC-10 have also experienced catastrophic failures of a door; the Boeing 747 has experienced a number of such incidents, the most noteworthy of which occurred aboard United Airlines Flight 811 in February 1989, when the cargo door failed and caused a section of the fuselage to fail, causing the deaths of 9 passengers who were expelled from the aircraft. A somewhat similar problem led to a cockpit window being blown off of British Airways Flight 5390.
[edit] Notable passengers
- Hubert 'Jake' Davies and Geoffrey Brigstocke, Britain's two leading authorities on law-of-the-sea
- Francis Hope, European correspondent for The Observer
- Jim Conway, secretary of Britain's second largest union, the AUEW
- Dr. Patrick Hutton, principal scientific officer at the British Atomic Weapons Research Establishment (AWRE)
- Dr. Charles Bowley, an internationally recognised authority on blood transfusion
- Graham Wood, former Mayor of Brighouse, West Yorkshire
- John Cooper, silver medallist in men's 400 m hurdles and 4x400 m relay at the 1964 Summer Olympics in Tokyo[3]
- Dr Wayne Wilcox, serving cultural attache at the US embassy in London and also chairman of Columbia University's political science department
[edit] See also
[edit] Footnotes
- ^ The control cables were not fully severed on American Airlines Flight 96 because American Airlines had installed a galley above the rear underfloor cargo door which reduced the weight on the cabin floor at that location.[citation needed]
[edit] References
- ^ "Turkish 981", Pilotfriend
- ^ Chris Kilroy, "Special Report: Turkish Airlines Flight 981", AirDisaster.com
- ^ Wallechinsky, David. (1984). The Complete Book of the Olympics. New York: Penguin Books. pp. 57, 67.
- Final Report, in French.
- Accident description at the Aviation Safety Network
- National Geographic Channel Mayday Turkish Airlines 981 Episode
[edit] External links
- Pre-crash photo taken from Airliners.net courtesy of M.Mailbrink
- Destination Disaster, by Paul Eddy et al., Quadrangle, The New York Times Book Company, 1976 ISBN 0-8129-0619-5.
- The Last Nine Minutes, The Story of Flight 981, by Moira Johnston, Morrow, 1976 ISBN 0-688-03084-X.
- Air Disaster, Vol. 1, by Macarthur Job, Aerospace Publications Pty. Ltd. (Australia), 2001 ISBN 1-875671-11-0, pp. 127-144.
- Sea of sand Ermenonville Paris
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