Turkish Airlines Flight 981

Turkish Airlines Flight 981

TC-JAV , the aircraft involved in the accident, in London Heathrow Airport, May 6, 1973.
Accident
Date	3 March 1974
Summary	Cargo door failure leading to explosive decompression, destruction of control systems, and loss of control
Site	Ermenonville Forest Fontaine-Chaalis, Oise, France 49°08.5′N 002°38′E
Aircraft
Aircraft type	McDonnell Douglas DC-10-10
Aircraft name	Ankara
Operator	Turkish Airlines
Registration	TC-JAVdisaster
Flight origin	Yesilköy Int'l Airport Istanbul, Turkey
Last stopover	Orly Airport Paris, France
Destination	London Heathrow Airport London, United Kingdom
Passengers	335
Crew	11
Fatalities	346 (all)
Survivors	0

Turkish Airlines Flight 981 was a McDonnell Douglas DC-10 that crashed outside Paris, France on 3 March 1974, killing all 346 people on board. The accident, also known as the "Ermenonville air disaster" from the forest where the aircraft crashed, is the deadliest accident involving a DC-10, the deadliest aviation accident to occur on French soil, has the fourth highest aviation death count ever, the second highest death count of a single-plane crash, and was the highest death toll of any crash until the Tenerife airport disaster three years later.

The crash resulted from the rear cargo hatch blowing off, causing decompression and severing cables that left the pilots with almost no control. The hatches used manual procedures to ensure they were locked correctly. Problems with the hatches had previously occurred. Investigation showed that these procedures were open to abuse, by forcing the handle shut without the pins being in place. It was noted that the pins had been filed down, making it easier to close the door, but leaving it less resistant to pressure. Also a support-plate for the handle-linkage had not been installed, although this work had been signed-off. Finally the latching had been performed by a Moroccan baggage-handler who could not read the relevant notices, in Turkish or English. After the disaster, the latches were re-designed and the locking system significantly upgraded. Flight 981's Captain was Nejat Berkoz, age 44, with 7,000 flying hours. First Officer Oral Ulusman, 38, had 5,600 hours flying time and Flight engineer Erhan Ozer, 37, had 2,120 flying hours experience.

Aircraft

The aircraft, a DC-10 Series 10 (production designation "Ship 29") was built in Long Beach, California as N1337U, meaning it was originally to be delivered to United Airlines, but the airline did not take delivery. Instead, it was leased to Turkish Airlines on 10 December 1972 as TC-JAV. The DC-10 involved in the crash of Flight 981 had 12 six-abreast first-class seats and 333 nine-abreast economy seats, a total of 345 passenger seats.

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 11 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 due to a strike by 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 six British fashion models, and 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 FL230, 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 the plane; 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.

Its wreckage was later found in the Ermenonville Forest, a state-owned forest at Bosque de Dammartin, in the commune of Fontaine-Chaalis, Oise. 6 passengers had been ejected over Saint-Pathus.

The aircraft had disintegrated. The post-crash fires were small as there were few large pieces of the aircraft left intact to burn. Of the 346 on board, only 40 bodies were visually identifiable. Nine passengers were never identified.

Passengers

Final tally of passenger nationalities
Nationality	Passengers	Crew	Total
Argentina	3	0	3
Australia	2	0	2
Belgium	1	0	1
Brazil	5	0	5
Cyprus	1	0	1
France	16	0	16
Germany	1	0	1
India	2	0	2
Ireland	1	0	1
Japan	48	0	48
Morocco	1	0	1
New Zealand	1	0	1
Pakistan	1	0	1
Senegal	1	0	1
Spain	1	0	1
Sweden	1	0	1
Switzerland	1	0	1
Turkey	44	11	55
United Kingdom	176	0	176
United States	25	0	25
Vietnam	1	0	1
Unknown	2	0	2
Total	335	11	346

167 passengers flew on the Istanbul to Paris leg, and 50 of them disembarked in Paris. 216 new passengers, many of whom were supposed to fly on Air France, BEA, Pan Am or TWA, boarded TK 981 in Paris. As a result, the layover increased from the normal one hour to one hour and thirty minutes. Some other passengers cancelled their tickets due to delays or for not finding enough seats.

Most of the passengers were British. Among the British passengers were members of an amateur rugby team from Bury St Edmunds, Suffolk, who were returning from attending a Five Nations match between France and England and trade union leader James Conway. The English rugby team took an Air France Boeing 727 instead of the doomed aircraft. Japanese embassy sources said that a total of 49 Japanese were on board. Turkish sources said that 15 Turks were on board. Also on board was John Cooper, who won silver medals in men's 400 meter hurdles and the 4X400 meter relay at the 1964 Summer Olympics in Tokyo.

Also among the passengers was Dr. Wayne Ayres Wilcox, a cultural attaché of the Embassy of the United States in London, his wife Ouida Rae (Neill) Wilcox, and two of his four children. 38 passengers were Japanese university graduates who were touring Europe and were planning to join Japanese firms after the end of their tour.

Investigation

The flight data recorder and cockpit voice recorder showed that the first hint the flight crew had of any problem was a muffled report that took place just after the aircraft passed over Meaux. That sound was followed by a loud rush of air, and the throttle for the tail-mounted Number 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 Berkoz and First Officer Oral Ulusman struggled to gain control. As its speed increased, the additional lift started to raise the nose again. Berkoz called "Speed!", and once more started to push the throttles forward, in order to level off. It was too late, however, and 72 seconds after decompression, the airliner slammed into the forest at a speed of about 430 knots (490 mph; 800 km/h), in a slight left turn. The speed of the impact caused the airliner to disintegrate.

The wreckage was so fragmented that it was difficult to tell whether any parts of the aircraft were missing. 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. A farmer soon telephoned in; the rear cargo hold hatch beneath the floor, portions of the interior floor, and six passenger seats, still holding dead passengers, had landed in a turnip field near the town of Saint-Pathus, approximately 15 kilometres (9.3 mi) south of the main crash site.

French investigators determined that the rear cargo hold hatch had failed in flight, and the cargo area had decompressed. The resulting difference in air pressure between the cargo area and the pressurized passenger cabin above it, which amounted to several 2 psi or 14 kPa, caused a section of the cabin floor above the open hatch to fail and blow out through the hatch, along with the passenger seats attached to the floor section. Control cables that ran beneath the section of floor were severed, and the pilots lost the ability to control the airliner's elevators, rudder, and Number 2 engine. Loss of control of these key components was then catastrophic to the pilots' ability to control the entire aircraft.

Lloyd's of London insurance syndicate, which covered Douglas Aircraft, retained Failure Analysis Associates (now Exponent, Inc.) to investigate the accident as well. In the company's investigation, Dr. Alan Tetelman noted that the pins on the cargo door had been filed down. He learned that on a stop in Turkey, the ground crews had had trouble closing the door. After less than 1⁄4 inch (6.4 mm) had been taken off the pins, they were able to close it effortlessly. It was proven by tests that the door subsequently yielded to about 15 pounds per square inch (100 kPa) of pressure, in contrast to the 300 pounds per square inch (2,100 kPa) that it had been designed to withstand.

Cause

The passenger doors on the DC-10 are of the plug door variety, which prevents the doors from opening while the aircraft is pressurized. The cargo hatch, however, is not. Owing to its large radius, the cargo hatch on the DC-10 could not be swung inside the fuselage without taking up a considerable amount of valuable cargo space. Instead, the hatch was swung outward, allowing cargo to be stored directly behind it. The outward-opening design allowed the hatch, in the event of a latch failure, to be blown open by the pressure inside the cargo area. To prevent that, the DC-10 used a latching system held in place by "over-center latches" – four C-shaped latches mounted on a common torque shaft that were rotated over latching pins ("spools") fixed to the aircraft fuselage. Due to their shapes, when the latches are in the proper position, pressure on the hatch does not place any torque on them that could cause them to open, and they actually further seat onto the pins. The latches were engaged by electric actuators, with a hand crank provided as a back-up.

To ensure this rotation was complete and the latches were in the proper position, the DC-10 cargo hatch design included a separate locking mechanism that consisted of small locking pins that slid behind flanges on the lock torque tube (which transferred the actuator force to the latch hooks through a linkage). When the locking pins were in place, any rotation of the latches would cause the torque tube flanges to contact the locking pins, making further rotation impossible. The pins were pushed into place by an operating handle on the outside of the hatch. If the latches were not properly closed the pins would strike the torque tube flanges and the handle would remain open, visually indicating a problem. Additionally, the handle moved a metal plug into a vent cut in the outer hatch panel: if the vent was not plugged the fuselage would not retain pressure, eliminating any pneumatic force on the hatch. Also, there was an indicator light in the cockpit that would remain lit if the cargo hatch was not correctly latched, controlled by a switch actuated by the locking pin mechanism.

The cargo door design flaw, and the consequences of a resulting in-flight decompression, had been noted by Convair engineer Dan Applegate in a 1972 memo, written after American Airlines Flight 96, another DC-10, had its cargo hatch open and separate in flight. In the ensuing investigation it was discovered that the handlers had forced the locking handle closed in spite of the fact that the latches had not fully engaged, because of an electrical problem. The incident 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 interfering with the torque tube flanges. 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 the case of Flight 96, the airliner was able to make a safe emergency landing as not all the underfloor cables had been severed, thus allowing the pilots limited control.^{see 'loading'}

In the aftermath of the Flight 96 incident, the NTSB made several recommendations. Its 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 additional loads onto 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 should be upgraded, the FAA also agreed with McDonnell Douglas that the additional venting would be too expensive to implement, and the FAA did not demand that this change be made.

TC-JAV, as 'Ship 29', had been ordered from McDonnell Douglas three months after the service bulletin was issued, and been delivered to Turkish Airlines three months after that. Despite this, the changes required by the service bulletin (installation of a support plate for the handle linkage, preventing the bending of the linkage seen in the Flight 96 incident) had not been implemented. The interconnecting linkage between the lock and the latch hooks had not been upgraded. Through either deliberate fraud or oversight, the manufacturer construction logs nevertheless showed that this work had been carried out. However, an improper adjustment had been made to the locking pin and warning light mechanism, causing the locking pin travel to be reduced. This meant that the pins did not extend past the torque tube flanges, allowing the handle to be closed without excessive force (estimated by investigators to be around 50 lbf or 220 N) despite the improperly engaged latches. This matches the comments made by Mohammed Mahmoudi, the baggage handler who had closed the door on Flight 981, who noted that no particular amount of force was needed to close the locking handle. Changes had also been made to the warning light switch, so that it would turn off the cockpit warning light even if the handle was not fully closed.

The fix that was implemented by McDonnell Douglas after the American Airlines Flight 96 incident was the addition of a small window that allowed the baggage handlers to visually inspect the pins, confirming they were in the correct position, and placards were added to show the correct and incorrect positions of the pins. This modification had been carried out on TC-JAV. However, Mahmoudi had not been advised as to what the indicator window was for. 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. Furthermore, the instructions regarding the indicator window were posted on the aircraft in English and Turkish, but the Algerian-born Mahmoudi, who could read and write three languages fluently, could not read either language.

It was normally the duty of either the airliner's flight engineer or the chief ground engineer of Turkish Airlines 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 members called for Mahmoudi to be arrested, the crash investigators stated that it was unrealistic to expect an untrained, low-paid baggage handler who could not read the warning sticker (due to the language difference) to be responsible for the safety of the aircraft.

Aftermath

Monument to the crash victims – Ermenonville Forest

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 seal the cargo hatch. 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 as out-of-pocket expenses by the fuselage's sub-contractor, Convair. Although Convair had informed McDonnell Douglas of the potential problem, rectifying what the aircraft manufacturer considered a small problem with a low probability of occurrence would have seriously disrupted delivery of the aircraft and cost sales so Convair's concerns were ignored. 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 the field of engineering ethics.

After the crash of 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-out door.

The death toll of 346 exceeded any other aviation fatality count for three years until 27 March 1977, when 583 people perished in the collision of two Boeing 747s in the Canary Islands. As far as a hull loss involving a single aircraft, the crash of Flight 981 remained the deadliest on record until 12 August 1985, when 520 were killed in the crash of Japan Airlines Flight 123.

The name given to the crashed DC-10, "Ankara", is still used on an Airbus A340-300 (TC-JDL, MSN: 57) in Star Alliance Livery. Turkish Airlines still flies to London, but the route is currently non-stop. The aircraft operated is an Airbus A330-300.

Dramatization

The story of the disaster was depicted in the fifth year of Canadian National Geographic Channel show Mayday (known as Air Emergency in the US, Mayday in Ireland and Air Crash Investigation in the UK and the rest of world). The episode is entitled "Behind Closed Doors". It was also featured in Loose Change 9/11: An American Coup.

Similar accidents

Outward-opening cargo hatches are inherently not fail-safe. An inward-opening hatch (a plug door) that is unlatched will not fly open, because the difference in air pressure between the aircraft cabin and the air outside will seal the hatch shut. However, an outward-opening, non-plug type hatch needs to be locked shut to prevent any unwanted opening. This makes it particularly important that the locking mechanisms be secure. American Airlines Flight 96 experienced the same problem before the Flight 981 accident, but the NTSB's recommendations to prevent it from happening again were not implemented by any airline. As a result, now whenever the NTSB comes up with recommendations to prevent certain accidents from happening, they talk to the FAA. Consequently, the FAA may issue an Airworthiness Directive to help prevent certain types of accidents from happening. However, NTSB and FAA are two independent Federal agencies, and the FAA is not obligated to act on NTSB recommendations. Aircraft types other than the DC-10 have also experienced catastrophic failures of a hatch. The Boeing 747 has experienced several such incidents. The most noteworthy of which occurred on United Airlines Flight 811 in February 1989, when the cargo hatch failed and caused a section of the fuselage to fail and resulted in the deaths of nine passengers expelled from the aircraft.

See also

• List of notable decompression accidents and incidents
• List of airliner crashes involving loss of control
• Japan Airlines Flight 123
• United Airlines Flight 232
• American Airlines Flight 96
• United Airlines Flight 811

Footnotes

• ^ The control cables were not completely severed on American Airlines Flight 96 because American Airlines had installed a galley above the rear cargo hatch beneath that cabin floor – that reduced the weight on the cabin floor in this location. The galley presumably weighed less than an equivalent number of passengers and their seats sitting in this same location.

Further reading

• 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.

External links

External image
Pre-crash photo at Hamburg Airport taken from Airliners.net courtesy of M. Maibrink

• Media related to Turkish Airlines Flight 981 at Wikimedia Commons
• Final Report (Archive, Alternate) – Bureau d'Enquêtes et d'Analyses pour la Sécurité de l'Aviation Civile – Translation by the United Kingdom Department of Trade Accidents Investigation Branch, February 1976.
• Template:Fr icon Final Report (Archive, Alternate, Archive of Alternate) – Original report by French Secretariat of State for Transport (Secrétariat d'État aux Transports) – Posted by the Bureau d'Enquêtes et d'Analyses pour la Sécurité de l'Aviation Civile (BEA)
• Accident description at the Aviation Safety Network