Africa

Shut down by enemy fire.

None of the assumptions i.e. Material failure, electrical failure, abrupt manoeuvre to avoid another aircraft and unfavorable weather conditions, satisfied the investigating commission as being a definite cause of the accident. The last one, however, although unlikely at first sight, could account for the accident if the crew warned of the deteriorating weather by the Anfa tower had decided to take advantage of the partial visibility (of the ground) between stratus cloud and had attempted a fast let-down in unfavorable conditions.

The accident was the result of an error of judgement on the part of the captain, who, after sighting the runway lights, concentrated on keeping them in sight and failed to make adequate reference to his flight instruments. As a result, he allowed the aircraft to descend below the obstacle clearance limit of 360 feet. In the darkness with no ground reference, the distant runway lights gave him insufficient guidance as to his height and angle of approach, and he was unaware that the aircraft had descended to ground level. The fatigue of the captain and the failure to put the aircraft's landing lights ON were considered as contributing factors.

The accident was caused by flight at too low an altitude during a night training exercise. According to witnesses, the instructor had directed the pilot to circle the runway at an altitude of 150 ft during the first training exercise; it appears that this instruction was maintained for the same exercise by night. Assuming that take-off was made with flaps extended, it so happened that complete retraction of the flaps occurred practically at the time of impact with the first tree. In fact, it can be estimated that the flight lasted 30 - 40 seconds from the time of take-off to impact with the first tree. Retraction of the landing gear takes ' 15 seconds and of the flaps approximately 10 seconds. Rapid retraction of the flaps at low speed causes the aircraft to nose down, It is possible that the loss of altitude occurred just before reaching the curtain of trees. Flaps are normally retracted gradually after reaching an altitude of 200 feet in visual meteorological conditions and 400 ft in instrument meteorological conditions or at night. The normal path of a DC-4 with one engine on reduced-power at take-off, climbing speed 400 - 500 ft/min, made it impossible for the aircraft to clear the tops of the trees which it struck. Assuming the take-off was made without flaps - a manoeuvre not recommended during night flights at Douala - the path followed would have inevitably brought the aircraft into the trees. It should be noted that the Air France DC-4 Manual prohibits counter-rotating the engine propeller in case of hydraulic Iock; this manoeuvre merely forces the oil into the intake pipe and can render the engine inoperative. Even though this prohibited manoeuvre was followed, it does not appear that it was one of the causes of the accident; the incident would most certainly have occurred during the first aerodrome circuit after the return to the parking area. In conclusion, it appears that the accident should be ascribed to lack of seriousness and judgement on the part of the instructor. Pilot fatigue may also be invoked after a two-hour training flight at very low altitude under the constant supervision of the instructor. The pilot was a very serious, methodic and calm flier, but he did not have sufficient authority to disregard the unduly risky manoeuvres urged upon him, as confirmed orally by a flight mechanic who had flown with the crew involved in the accident.

The accident was caused by the pilot-in-command inattention to his instruments.

It is believed that the probable cause of the accident was an act of sabotage with the denotation of a nitrocellulose explosive device. The reasons and the authors of this act remains unknown.

Engine failure during initial climb.