Turkish Airlines Flight 981

Turkish Airlines Flight 981

TC-JAV, the aircraft involved in the accident, taxiing at London Heathrow Airport, 6 May 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	336
Crew	11
Fatalities	346
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 crash, also known as the Ermenonville air disaster, from the forest where the aircraft crashed, is the deadliest crash involving a DC-10, the deadliest plane crash on French soil, the fourth-deadliest plane crash in aviation history, the deadliest single-plane crash with no survivors, has the second-highest number of fatalities in a single-plane crash (behind Japan Airlines Flight 123), and had the highest death toll of any air disaster until the Tenerife airport disaster three years later.

The crash was caused when an improperly secured cargo door at the rear of the plane broke off, causing an explosive decompression which severed cables necessary to control the aircraft. Because of a known design flaw left uncorrected before and after the production of DC-10s, the cargo hatches did not latch reliably, and manual procedures were relied upon to ensure they were locked correctly. Problems with the hatches had occurred previously, most notably in an identical incident that happened on American Airlines Flight 96 in 1972. Investigation showed that the handles on the hatches could be improperly forced shut without the latching pins locking in place. It was noted that the pins on the hatch that failed on Flight 981 had been filed down to make it easier to close the door, resulting in the hatch being less resistant to pressure. Also, a support plate for the handle linkage had not been installed, although this work had been documented as completed. Finally, the latching had been performed by a Moroccan baggage handler who could not read relevant warning notices in Turkish and English. After the disaster, the latches were redesigned and the locking system significantly upgraded.

Flight 981's captain was Nejat Berköz, age 44, with 7,000 flying hours. First Officer Oral Ulusman, 38, had 5,600 hours flying time, and Flight Engineer Erhan Özer, 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, under the manufacturer's test registration N1337U, and leased to Turkish Airlines as TC-JAV, on 10 December 1972. It had 12 six-abreast first-class seats and 333 nine-abreast economy seats, for 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 was carrying just 167 passengers and 11 crew members in its first leg. 50 passengers disembarked in Paris. The flight's second leg, from Paris to London Heathrow Airport, was normally underbooked, but due to strike action by British European Airways employees, many London-bound travellers 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 left Orly around 12:30 pm, bound for 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, towards London. Just after Flight 981 passed over the town of Meaux, the rear left cargo door blew off. The sudden difference between the air pressure in the cargo area and the pressurised passenger cabin above it, which amounted to 2 pounds per square inch or 14 kilopascals, caused a section of the cabin floor above the open hatch to fail and blow out through the hatch, along with six occupied passenger seats attached to the floor section. The rear hatch and the passengers' bodies landed in a turnip field near Saint-Pathus, approximately 15 kilometres (9.3 miles) south of where the remainder of the plane would crash. 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, likely the remains of the rear cargo door.

When the door blew off, the control cables that ran beneath the section of floor sucked out were severed, and the pilots lost the ability to control the plane's elevators, rudder, and Number 2 engine. The flight data recorder showed that the throttle for Engine 2 snapped shut when the door failed. Loss of control of these key components meant that the pilots lost control of the aircraft entirely.

The aircraft almost immediately attained a 20-degree, nose-down attitude, and started picking up speed, while Captain Berköz and First Officer Ulusman struggled to regain control. At some point, one of the crew pressed his microphone button, broadcasting the pandemonium in the cockpit on the departure frequency. Controllers also picked up a distorted transmission from the plane; the aircraft's pressurisation and overspeed warnings were heard over the pilots' words in Turkish, including the co-pilot saying "the fuselage has burst!" As the plane's speed increased, the additional lift started to raise the nose again. Berköz called "Speed!" and once more started to push the throttles forward, to level off. It was too late, however, and 72 seconds after the door broke off, the plane slammed into the trees of Ermenonville Forest, a state-owned forest at Bosque de Dammartin, in the commune of Fontaine-Chaalis, Oise. At the point of impact, the aircraft was travelling at a speed of about 430 knots (490 mph; 800 km/h) in a slight left turn, fast enough that the plane disintegrated into millions of pieces instantly. The wreckage was so fragmented that it was difficult to tell whether any parts of the aircraft were missing. The post-crash fires were small, as there were few large pieces of the aircraft left intact to burn. Of the 346 passengers and crew 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
1968	5	0	5
1960	1	0	1
France	16	0	16
West 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
South 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 because of delays or a lack of seats.

The majority 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. The English rugby team took an Air France Boeing 727 instead of the doomed aircraft. Also on board were John Cooper, who won silver medals in men's 400 metres hurdles and the 4 × 400 metres relay at the 1964 Summer Olympics in Tokyo, and trade union leader James Conway.

Other passengers included 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, as well as 48 Japanese university graduates who were touring Europe, and planning to join Japanese firms after their tour.

Investigation

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. They filed the pins down, reducing them by less than a quarter of an inch (6.4 millimetres), and were then able to close the door effortlessly. It was proven by tests that the door subsequently yielded to about 15 psi (100 kPa) of pressure, in contrast to the 300 psi (2,100 kPa) that it had been designed to withstand.

Cause

The passenger doors on the DC-10 are plug doors, designed to prevent their opening while the aircraft is pressurised. 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 designed to open outward, allowing cargo to be stored directly behind it. The outward-opening design allowed the hatch to be blown open by the pressure inside the cargo area if the latch failed during flight. To prevent this, the DC-10 used a latching system incorporating "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 shape, when the latches were in the proper position, internal pressure on the hatch did not place any torque on them that could cause them to open; they actually seated further onto the pins. The latches were engaged by electric actuators, with a hand crank provided as a backup.

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, controlled by a switch actuated by the locking pin mechanism, that remained lit unless the cargo hatch was correctly latched.

Similarities to American Airlines Flight 96

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. The memo was written after American Airlines Flight 96, another DC-10, had an rear cargo door failure identical to the one that occurred on Flight 981, causing an explosive decompression. Even though the pilots' ability to control the aircraft was compromised by the severing of some of the underfloor cables in the blown-out section of the plane, they were able to land it in Detroit without any further injuries. The NTSB's investigation into Flight 96 found that the handlers had forced the locking handle closed, in spite of the fact that the latches had not engaged fully 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. 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 devices indicated that the door was properly closed. In the case of Flight 96, the plane was able to make a safe emergency landing because not all of the underfloor cables were severed, thus allowing the pilots limited control. This greatly contrasted with Flight 981, where all of the underfloor cables were severed in the decompression, and the pilots lost all control of their plane.

In the aftermath of Flight 96, 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 equalise 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, it also agreed with McDonnell-Douglas that the additional venting would be too expensive to implement, and did not demand that this change be made.

The plane that crashed as Flight 981, TC-JAV, or "Ship 29", had been ordered from McDonnell-Douglas three months after the service bulletin was issued, and was delivered to Turkish Airlines another 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 oversight or deliberate fraud, the manufacturer construction logs nevertheless showed that this work had been carried out. An improper adjustment had been made to the locking pin and warning light mechanism, however, 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 pounds-force or 220 newtons) despite the improperly engaged latches. These findings concurred with statements made by Mohammed Mahmoudi, the baggage handler who had closed the door on Flight 981; he 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.

After Flight 96, McDonnell-Douglas added a small peephole that allowed the baggage handlers to visually inspect the pins, confirming they were in the correct position, and placards to show the correct and incorrect positions of the pins. This modification had been carried out Flight 981's plane. However, Mahmoudi had not been instructed about the purpose 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 safely latched. Furthermore, the instructions on the plane regarding the indicator window were printed in English and Turkish, but Algerian-born Mahmoudi, who was fluent in three other languages, could read neither of these.

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 outlets 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 to be responsible for the safety of the aircraft.

Aftermath

Monument to the crash victims in 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 were routed under the floor. Therefore, a failure of the hatch that resulted in a collapse of the floor could impair the controls. If the hatch were to fail for any reason, there was a very high probability the plane would be lost. To make matters worse, Douglas chose a new type of latch to seal the cargo hatch. This possibility of a catastrophic failure as a result of this overall design 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 subcontractor, Convair. Although Convair informed McDonnell Douglas of the potential problem, Douglas ignored these concerns, because rectification of what Douglas considered to be a small problem with a low probability of occurrence would have seriously disrupted the delivery schedule of the aircraft, and caused Douglas to lose sales. 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 redesign of the latching system was finally implemented. The latches themselves were redesigned 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 forced closed without the pins in place, and the vent door was altered to be operated by the pins, thereby indicating when the pins, rather than the handle, were in the locked position. 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 equalise in the event of a blown-out door.

The death toll of 346 exceeded that of any previous aviation incident. Three years later, on 27 March 1977, 583 people perished in the collision of two Boeing 747s in the Canary Islands. Flight 981 remained the deadliest accident resulting from hull loss, involving a single aircraft, until 12 August 1985, when 520 were killed in the crash of Japan Airlines Flight 123, and the deadliest aviation accident with no survivors until the Charkhi Dadri mid-air collision of 12 November 1996 which killed 349 people. As of 2013, Flight 981 is still the deadliest single-plane accident with no survivors (there were four on JAL 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, and flown with an Airbus A330-300.

Similar accidents

An outward-opening cargo hatch is inherently less resistant to blowing open than an inward-opening one, also called a plug door. In flight, the air pressure inside the aircraft is greater than that outside, and pushes outward on the hatch. In the case of a plug door, this actually seals the door more tightly. An outward-opening hatch, however, relies entirely upon its latch to prevent it from opening in flight. This makes it particularly important that the locking mechanisms be secure. Aircraft other than DC-10s have also experienced catastrophic failures of hatches. The Boeing 747 has experienced several such incidents, the most noteworthy of which occurred on United Airlines Flight 811 in February 1989. On Flight 811, the cargo hatch failed, causing a section of the fuselage to fail, resulting in the deaths of nine passengers, who were blown out of the aircraft.

The NTSB's recommendations following the earlier Flight 96 incident, which were intended to decrease the possibility of another hatch failure, were not implemented by any airline. As a result, the NTSB now communicates directly with the FAA regarding the former's recommendations for safety improvements, and the FAA may issue Airworthiness Directives based on those recommendations. However, the FAA is not obligated to act on NTSB recommendations.

In media

Flight 981 and American Airlines Flight 96 were examined in "Behind Closed Doors", an episode from the fifth season of the Canadian National Geographic Channel series Mayday (US series title: Air Disasters; international title: Air Crash Investigation).

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

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