(Image embedded from wikipedia)
Aircraft Type: McDonnell Douglas DC-10-10
Name of Aircraft: Ankara
Registration Marks: TC-JAV
Location of accident: Ermenonville forest France
Oringin: Yeşilköy International Airport (Istanbul Ataturk International Airport)
Destination: London Heathrow Airport
Time of accident: About 1142 hrs GMT
Flight Crew: 3
Cabin Crew: 10
Engines: General Electric CF6-6D
On 3rd March, 1974,Turkish Airlines Flight 981, a McDonnell Douglas DC-10 departed Istanbul for a flight to Paris and London when it crashed in a forest at Ermenonville, France. The pilots lost control of the aircraft following an explosive decompression in its cargo hold. Some people at the rear were sucked out of aircraft.
During flight a rear cargo door on the left came off. This resulted in a rapid depressurisation in the cargo compartment. The air pressure difference between the passenger cabin and the cargo hold caused the floor to partially collaspe. Two rows of seats in the cabin were ripperd off. The control cables to the horizontal stabillizer and the elevators which ran under the floors of were severed, resulting in loss of control. In addition, the airplane lost power from engine number 2. The plane turned to the left and pitched nose down. Pitch attitude increased to -20 degrees and speed increased to 360 knots. It then levelled out at a pitch attitude of -4 degrees ,remained at a speed of 430 knots and banked 17 degrees to the left prior to crashing. The impact killed all remaining crew and passengers on board.
1. From Flight to Impact
(Video embeded from Youtube on 26 September 2009)
2. Door problem explained (Part 1)
American Airlines Flight 96, experienced a similar problem on 12 June 1972, except they were luckier. The crew managed to land safely at Detroit Michigan.
(Video embeded from Youtube on 28 September 2009)
Door problem explained (Part 2)
(Video embeded from Youtube on 28 September 2009)
How does the cargo door latch work?
See the animation at: http://lessons.workforceconnect.org/reflib/paran/
Analysis of the accident
The Swiss Cheese Model
This model was proposed by a British psychologist James Reason in 1990. It helps explain how various contributory factors come together to culiminate in an accident. For this reason, it is also known as the cumulative act effect. The slices of Swiss cheese illustrates a system’s defense against failures. The holes represent deficiencies in individual parts of a system. The type of deficiencies are:
Errors that have not immediate impact on the well being of a system. They arise from decisions made by people such as designers, manufacturers, regulators, top managers and procedure writers. Such errors lie dormant in a system, untill combined with active errors or appropriate triggers to create an accident. Some latent errors are harder to catch, in in the this case, they are obvious.
Errors that have an immediate effect on the system. They are usually commited people who are in direct contact with a system e.g pilots.
Reason also states that most of the accidents can be attributted to one or more of the 4 levels of failure:
- Level 1: Organizational influences
- Level 2: Unsafe supervision
- Level 3: Preconditions for unsafe acts
- Level 4: Unsafe acts themselves
See animation at of the model at: http://lessons.workforceconnect.org/reflib/defan
As the animation illustrates, accidents can be prevented at any stage along the way by taking the appropriate actions. Accidents happen when holes in the layers align permitting a hazard to pass through all the defences, which Reason described it as "a trajectory of accident opportunity". This model is also used by other industries where safety is paramount such as in the healthcare industry.
This crash was certainly not caused by an isolated event. Rather it took a culimination of design, organisational, management and human errors before the accident finally took places. In the TK981 case, the chain of latent errors leading up to the crash of are:
Latent Error 1
Macdonnell Douglas: Serious design flaws in the DC-10.
Latent Error 2
Macdonnell Douglas: The company that maufactured the cargo door for Macdonnell Douglas warned that the lack of vents in the floors and the design of the doors will eventually lead to a disaster. But MD did nothing about it.
American Airlines lost their cargo door in flight. After an investigation by NTSB, recommendations were made to modify the latching mechanism and add vents to the floors of the airplane.
Latent Error 3
Macdonnell Douglas: Did not implement the recommendations in the manufacturing process.
Latent Error 4
Federal Aviation Adminitration: Compromised their position as an aviation authority. After American Airlines lost their cargo door in flight, FAA At first prepared an Airworthiness Directive requiring all DC-10s to be grounded untill the required modifications are made, but the President of Maconnell Douglas managed to persuade the head of FAA to downgrade the urgency as he was afraid that the AD would affect the sales of the airplane. Unfortunately FAA gave in. It downgraded the urgency and issued a Service Bulletin instead.
Latent Error 5
Turkish Airlines (THY) : Did not see the urgency for the modifications and therefore give did not instructions to carry it out.
Latent Error 6
THY: THY neither fix the fatigue problemin the locking pins. This could reflect some organisational possible problems with THY, most probably with the:
- Feedback System
- Reporting System
Latent Error 7
Baggage Handler: Inadequate training. An Algerian handler was asked to close the cargo door. He knew how to close it but not how to use the window which MD added for inspection purposes. Like many other handlers, he did not known what the windows were for. In addition he found it surprising easy to lock the door due to fatigue which is already present in the locking pins. Neither did he understand the instructions or the warning placard as he speaks no English or Turkish. If he had been taught how to inspect the locking pins were for or the right amount of force needed to close the door (with his sense of touch), he could have known that something was not right.
Active Error 8
Neither a member of the flight crew nor a ground engineer did a final inspection before flight. Since the flight was already behind time, the pressure to take off and make up for lost time led the crew to overlook the need for final inspection.
Finally the the plane crashed.
Impact of the crash on Macdonell Douglas
The crash have botched their reputation. They were ordered to pay a heavy compensation to the families of the victims and orders for their products dropped significantly. The company was later acquired by Boeing.
The crash of TK981 illustrates that in accident investigations, it is not enough to just focus on the accident itself. All contributory factors have to be taken into account. At every step of the way, i.e from design up to the time where the DC-10 crashes, there is potential for errors to be introduced. As it is the very nature of humans to makes mistakes, no system can therefore be perfect. Also as the complexity of a system increases, so is the potential for harmful consequences.
After the crash, Macdonell Douglas finally carried out modifications to the cargo doors. In addition, FAA issued an AD requiring all DC-10s to be grounded untill the required modifications are made.
Finally, safety should come before profits in high reliability industries.
Want to know more?
http://aviation-safety.net/database/record.php?id=19740303-1 : More about the accident.
http://patientsafetyed.duhs.duke.edu/module_e/swiss_cheese.html : The Swiss Cheese Model.