ASN News Crew in fatal Mali MD-83 accident likely failed to use anti-icing systems, says interim report

Engine Pressure Ratio values (registered and re-calculated) of the accident flight

A progress report by the Mali investigators stated that the crew of an MD-83 that crashed in July 2014, killing all 116 on board, likely failed to use anti-icing systems.

The aircraft, operated by Swiftair on behalf of Air Algérie, had departed Ouagadougou, Burkina Faso on a flight to Algiers, Algeria. The plane reached the cruise altitude of 31,000 ft and the autopilot was used in altitude hold mode and the auto-throttle speed (Mach) hold mode.

Analysis of the recorded parameters by the flight data recorder, indicates that about two minutes after the leveling off at FL310, the engine pressure ratio (EPR) value became become incoherent in relation to other engine parameters. This anomaly occurred on the right engine and about 55 seconds later on the left engine. These false readings were probably caused by an obstruction of

the pressure sensors located on the nose cone of the engine, presumably by icing. This icing may have been caused by the presence of cold, moist air on the edge of the storm cell, considering

the fact that none of the anti-icing systems were activated.

Due to the incorrect values, the auto-throttle tried to maintain a lower thrust than was necessary. The aircraft lost speed and developed a tendency to descend. The autopilot, engaged in altitude hold mode, then attempted to raise the nose in order to maintain altitude. The aircraft ultimately stalled.

Approximately 20 seconds after the start of the aircraft stall, the autopilot disconnected. The plane then suddenly rolled to the left until it reached 140° bank angle and 80° nose down pitch.

At this stage of the investigation, it could not be determined whether the autopilot disconnection from a action of the crew or if this was an automatic disconnection.

The investigators found two related incidents in which the crew were able to recover. In June 2002 an MD-82 stalled when engine power rolled back in cruise. Another incident occurred in June 2014 when a Swiftair MD-83 suffered a similar situation with the crew recovering before the aircraft was able to enter a stall.

The investigation is ongoing with a report expected to be published in December 2015.

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Filed under: Investigation Reports by Harro Ranter

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