Mali

About two minutes after leveling off at an altitude of 31,000 ft, calculations performed by the manufacturer and validated by the investigation team indicate that the recorded EPR, the main parameter for engine power management, became erroneous on the right engine and then about 55 seconds later on the left engine. This was likely due to icing of the pressure sensors located on the engine nose cones. If the engine anti-ice protection system is activated, these pressure sensors are heated by hot air. Analysis of the available data indicates that the crew likely did not activate the system during climb and cruise. As a result of the icing of the pressure sensors, the erroneous information transmitted to the auto throttle meant that the latter limited the thrust delivered by the engines. Under these conditions, the thrust was insufficient to maintain cruise speed and the aeroplane slowed down. The autopilot then commanded an increase in the airplane's pitch attitude in order to maintain the altitude in spite of this loss of speed. This explains how, from the beginning of the error in measuring the EPR values, the airplane’s speed dropped from 290 kt to 200 kt in about 5 minutes and 35 seconds and the angle of attack increased until the aeroplane stalled. About 20 seconds after the beginning of the aeroplane stall, the autopilot was disengaged. The aeroplane rolled suddenly to the left until it reached a bank angle of 140°, and a nose-down pitch of 80°. The recorded parameters indicate that there were no stall recovery maneuvers by the crew. However, in the moments following the aeroplane stall, the flight control surfaces remained deflected nose-up and in a right roll. It was concluded that the accident was caused by the combination of several factors, among them the fact that the engine anti-icing systems were not activated by the crew. The final report is not available in English yet.

The Accident Investigation Board (AIB) President found by clear and convincing evidence that the cause of this mishap was the mishap aircraft running out of fuel due to the mishap aircraft commander’s and mishap copilot’s failure to properly fuel plan and then refuel the mishap aircraft at Nouakchott with a sufficient amount to reach their destination. Once airborne, despite indications of a fuel shortage, the mishap crew did not divert to a suitable alternate airport early enough in the sortie to avoid this mishap. The AIB President also found sufficient evidence to conclude the following factors substantially contributed to the mishap: insufficient mission and flight planning; faulty decision-making; complacency; task misprioritization; channelized attention; and the mishap crew pressing to meet mission demands.

Loss of control after landing due to strong crosswinds in thunderstorm activity.