SNCASE SE.161 Languedoc

The above leads to the conclusion that if the accident was due to meteorological factors, icing would have been the factor most directly responsible. It is assumed that during its flight through innocuous stratiform clouds, the aircraft may have encountered a cumulus congestus where sudden severe icing occurred. The following may have taken place:
a) a sudden change in the aerodynamic characteristics of the aircraft may have caused stalling without giving the captain time to initiate recovery action,
b) the aircraft may have lost height rapidly, down to a level where the downdrafts over the lee slope swept it into a lower zone of erratic turbulence that sent it out of control,
c) when icing occurred, the captain may, in the belief he had already passed the mountain divide, have decided to fly below the freezing level which, as he knew, was to be found at about 2 200 metres. It is possible that in assumptions (a) and (b) turbulence within the cumuli may have been a contributing factor. Under severe icing conditions, the mechanical de-icing equipment is practically inoperative. About 40 minutes before the accident, the mountain divide was over- flown, also at level 95, by a scheduled Santiago-Madrid flight. This aircraft found nothing unusual to report, since light icing and turbulence are the normal accompaniments of winter weather in a low pressure area. This fact however, in no way precludes the possibility that shortly thereafter conditions of severe icing may have prevailed.

Failure of the right main gear on landing. It appears it was down but not locked for unknown reasons.

The accident was due to a loss of power followed by a sudden picking up of no. 1 engine, added to the inherent tendency of the aircraft to veer to the left. The flight engineer noticed this loss of power but did not warn the pilot before checking the instruments at his own station. Having noticed that his instruments read normally, and finding, on turning back to the pilot's panel, that the engine had picked up, he did not consider it necessary to report the loss of power to the pilot-in-command. The pilot-in-command must have presumed the swerving of the aircraft to be normal and have corrected the motion of the aircraft on that basis. Owing to the complexity of the flight engineer's duties on take-off and to the fact that he had to stand, thus being subject to inertia and centrifugal forces, he was hampered and delayed in his motions. The aircraft was destroyed as a result of the fact that, in running over sandy ground its left wheel sank into a soft spot causing the left attachment fitting of the left landing gear to break. In collapsing, the landing-gear caused no. 1 and, no. 2 engines to come into contact with the ground. The fuel cocks and the cut-off valves were not closed. Fire broke out on the left wing, and destroyed the aircraft.

The loss of control occurred when the crew decided to raise the flaps, apparently following an asymmetric issue.

The exact cause of the failure of the engine number one could not be determined with certainty. However, it would appear that the pilot showed a poor knowledge of the airplane, especially on the following items:
- The fire warning system had not operated nor had the automatic extinguishers, indicating that the nacelle temperature could not have risen appreciably. The extinguisher had been manually operated.
- He should not have restarted the defective motor after a fire and with almost a full load.
- If the main undercarriage systems had failed to function, he should have operated the first and the second emergency systems.

It was decided that the unusual path of the aircraft immediately following the take-off, was due to the blocking of the ailerons to the left at an angle of approximately 10 degrees. It was determined on the basis of analysis that the probable cause of the blocking was the unclamping of a link cheek of the upper rear chain of the co-pilot's control column, as a result of which the chain slipped off the sprocket and jammed against the internal boss of the pin which locks the ailerons in the neutral position. More broadly, the investigation brought to light the difficulty of setting and inspecting the chains inside the dual control columns. This difficulty is directly attributable to the design, and may cause certain chains which have not been properly studied in relation to the type of service for which they are intended, to become unclamped by torsion during maintenance and setting work.