Africa

The accident was caused by failure of the pilot to execute a successful single engine forced landing after concluding that there had been a power loss in the port engine. Evidence indicated that a failure of the port engine did not, in fact, occur. The pre-take-off rudder trimmer check was not carried out correctly as laid down in the checklist, and the aircraft took off with full left rudder trim applied. Once airborne this was misinterpreted as port engine failure, and the port propeller was feathered. No apparent action was taken by the pilot to correct the ensuing critical speed yaw.

Investigations determined that the loss of control that occurred shortly after takeoff was caused by the movement of the safety catch located on the rails of the copilot's seat that dislodged. This caused the seat to slid on its rails back to the stop. As a result, the copilot involuntarily pull the control column, causing the aircraft to nose up and to stall due to an excessive angle of attack. It was determined that the copilot was flying when control was lost after rotation, which was non compliant as he did not have a licence allowing him to perform a takeoff with passengers on board.

It was strongly urged that the Commission should not conclude that the accident was due to pilot error. Reasons have been given for saying that other suggested causes were not really possible. Reasons have also been given for concluding that the approach was made by a visual descent procedure in which the aircraft was brought too low. It could not be said whether that came about as a result of inattention to the altimeters or misreading of them. The Commission felt it must conclude that the aircraft was allowed, by the pilots, to descend too low. In so doing it struck trees and crashed.
COMMENTS FROM THE UNITED NATIONS:
The Commission has carefully examined all possible causes of the accident. It has considered the possibility of sabotage or of attack and the material or human failures which could have resulted in an accident. It has found no evidence to support any of the particular theories that have been advanced nor has it been able to exclude the possible causes which it has considered. In this connexion it notes that the United Nations and the Swedish Observers who participated in the work of the Rhodesian Board of Investigation also expressed the opinion that it was impossible to exclude any of the possible causes which they considered or to establish an order of priority among them. With respect to sabotage it has noted that the aircraft was without special guard while it was at N'Djili Airport in Léopoldville and access to it was not impossible. The Commission is aware that there are many possible methods of sabotage. No evidence of sabotage has come to its attention but the possibility cannot be excluded. The possibility of attack from either the air or the ground has also been fully examined. The Commission has found no evidence that an attack of any kind occurred It has also noted the opinion of experts that it is improbable that the plane would have been in the apparently normal approach position indicated by the crash path and wreckage analysis had it been under attack. Nevertheless, it cannot exclude attack as a possible cause of the crash. The Commission has also considered various possibilities of material failure, including technical or structural defects, altimeter failure or fire in flight. A thorough analysis of that part of the wreckage capable of being examined was made by technical experts, including members of the Rhodesian Board of Investigation and United Nations and Swedish observers. The altimeters were examined in the United States by the Civil Aeronautics Board and the manufacturer. No evidence of material failure of the aircraft was found, but this possibility cannot be excluded, mainly because of the destruction of a major part of the aircraft by fire. The Commission also considered various possibilities of human failure. It found no evidence that any of the pilots had been incapacitated. It cannot, however, completely exclude this possibility as some forms of incapacity might not be revealed by a post-mortem examination, It also considered various possibilities of pilot error, including the use of a wrong instrument approach chart or a misreading of altimeters. It noted that the Rhodesian inquiry, by eliminating to its satisfaction other possible causes, had reached the conclusion that the probable cause of the crash was pilot error. The Commission, while it cannot exclude this possibility, has found no indication that this was the probable cause of the crash. The Commission considered the possibility that during the course of a visual or semi-visual approach or through the use of an instrument procedure involving a descending turn, the aircraft might have come below the accepted safety margin of 1 000 ft above ground level. On some landing charts, information concerning exact elevations in the approach area is not provided and should the aircraft have descended below the accepted margin a momentary distraction, either from inside or outside the aircraft, might have caused the pilot to lose the remainder of his margin of safety. The Commission however, has found no evidence that this could have been a possible cause of the crash. The Commission considers it its duty to record that it has examined the various rumors that have come to it, attention concerning the cause of the crash and has found no evidence in their support.

Shot down.

In the opinion of the board of inquiry of all the theories listed above, those related related to material failure appear the least likely. On the other hand, the theory regarding an error in instrument reading appears more probable than the others. Therefore, the Board explained the failure:
1) by the fact that reading of the Kollsman window altimeter, with which this Caravelle was equipped, may be delicate, as demonstrated by some systematic tests carried out by highly trained crews of various European airlines ;
2) by the possibility that the pilot made that error of 1,000 feet at the beginning of the descent, retaining it, then gave his full attention to reading the pointer, which seemed to him to be of prime importance, in order to bring in the aircraft at the minimum authorized altitude.

Failure of the nose gear on landing.