During the approach, the crew decided, without preparation, and specifically without any callout of the theoretical minimum speeds indicated in the document at their disposal, to undertake the check on the angle of attack protections in normal law at an altitude of about 4,000 feet. However, the blockage of angle of attack sensors 1 and 2 at identical values had inhibited the functioning of these protections and led to an erroneous display of the characteristic speeds of these protections.
The crew waited for these protections to be triggered while allowing the speed to decrease. The first triggering of the stall warning in normal law, at an angle of attack close to the theoretical angle of attack in landing configuration, indicates that angle of attack sensor 3 was functioning at that moment. The Captain reacted in accordance with the technique for approach-to-stall by increasing engine thrust and reducing longitudinal pitch.
Shortly after this, the flight control law changed from normal to direct due to a difference in the speed measurements. For this reason, after having progressively moved the horizontal stabiliser to the full pitch-up position during the deceleration, the autotrim system was no longer available. The horizontal stabiliser remained in this position until the end of the flight. Under the combined effect of the thrust and the increase in speed, the aeroplane was subject to a pitch-up moment that the Captain was not able to counter. The Captain did not react with any input on the trim wheel at any time or to reduce engine thrust in any prolonged manner.
Due to the position of the stabilizer and the pitch-up moment generated by the engines at full thrust, the crew lost control of the aeroplane during the increase in thrust. The aeroplane was completely destroyed on impact with the surface of the sea.
Auto trim paralysis strikes again....