Conclusions TC-JAV

7 Conclusions

Results of the Inquiry
The findings of the Inquiry are as follows:

The crew members held the certificate, licences and qualifications required for the performance of their duties in the type of aircraft and on the flight in question.

The aircraft was certificated, equipped and operated in accordance with national and international requirements; both on take-off and at the type of the accident, its load and centre of gravity position were within the appropriate limits.

Nevertheless, as regards the aft cargo door on the left-hand side:

A Service Bulletin 52-37, specifying the installation of a support plate designed to prevent forced closing of the 1ocking handle and the vent door in the case of incomplete engagement of the latching system, had not been applied to the air-craft before delivery and this oversight had not 5een detected at the time of delivery. It was found, however, that work on the application of this modification had begun on the lock tube where chamfering had been roughly carried out.

While the aircraft was in service, a modification (direct access to the drive mechanism) had been carried out in a way which did not comply with Service Bulletin S2-38.

The adjustments of the lock pins and the lock limit warning switch were incorrect.

The striker of the unIock limit switch had two shims of Douglas origin, surmounted by a shim with no reference and of a quality not to aeronautical standards.

During the aircraft’s stop at Orly, the aft cargo door on the left-hand side had been closed without any apparent abnormality, the locking handle had been pulled down and the vent door closed, although the 1ock pins were not engaged and no visual inspection had been made through the view port provided for the purpose of verifying that the lock pins were in place.

The take-off and climb progressed without incident until the aircraft reached approximately 12,000 feet at about 1140 hrs.

At that time, the aft cargo door on the left-hand side opened in flight and became detached from the aircraft structure.

The drop in pressure in the cargo compartment caused an immediate pressure differential which was sufficient to cause the disruption of the floor structure and the consequent ejection of six passengers, their cabin seats and various pieces of wreckage.

The deformation and disruption of the floor led to serious impairment of the controls af Ho 2 engine and of the flight controls of which,the cables run under this part of the aircraft structure and the damage was such that it was impossible for crew to regain control of the aircraft.

Because of the design of the mechanism as a whole the incomplete application of modification SB 52-37 (absence of support plate specified) and the adjustments found on measurement to"incorrect (lock pins and striker) it was possible for the door locking handle,to be pulled, down without the use of-any abnormal force and for the flight deck visual warning light to be switched off, when the latches were not fully engaged and the lock pins not in place. The tests and research have confirmed incomplete engagement of the cargo door latches and in correlation the non-engagement of the lock pins.

The Inquiry into an accident at Windsor (Ontario) on 12 lune 1972 had provided evidence of the grave risks entailed by sudden depressurization, of. the, cargo compartment: the inadequacy of the pressure relief vents had resulted in the disruption of the floor under which the flight control cables and, thereby causing the jamming or rupture of the cables.

5.2 Causes of the accident

The accident was the result of the ejection in flight of the aft cargo door on the left-hand side: the sudden depressurization which followed led to the disruption of the floor structure, causing six passengers and parts of the aircraft to be ejected, rendering No 2 engine inoperative and impairing the flight controls (tail surfaces) so that it was impossible for the crew to regain control of the aircraft.

The underlying factor in the sequence of events leading to the accident was the incorrect engagement of the door latching mechanism before take-off. The characteristics of the design of the mechanism made it possible for the vent door to be apparently closed and the cargo door apparently locked when in fact the latches were not fully closed and the lock pins were not in place.

It should be noted, however, that a view port was provided so that there could be a visual check of the engagement of the lock pins.

This defective closing of the door resulted from a combination of various factors:

incomplete application of Service Bulletin 52-37;

incorrect modifications and adjustments which led, in particular, to insufficient protrusion of the lock pins and to the switching off of the flight deck visual warning light before the door was locked; the circumstances of the closure of the door during the stop at Orly, and, in paiticular, the absence of any visual inspection, through the view port, ta verify that the lock pins were effecfively engaged, although at the time of the accident inspection was rendered difficult by the inadequate diameter of the view port

Finally, although there was apparent redundancy of the flight control systems, the fact that the pressure relief vent between the cargo compartment and the passenger cabin were inadequate and that all the flight control cables were routed 'beneath the floor placed the aircraft in grave danger in the case of any sudden depressurization causing substantial damage to that part of the structure.

All these risks had already become evident, nineteen months earlier, at the time of the Windsor accident, but no efficacious corrective action had followed.

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Department of Trade
ACCIDENTS investigation BRANCH

Turkish Airlines DC-10 TC-JAV Report on the accident in the Ermenonville Fozest, France on 3 March 1974