Sensor icing likely cause of Air Algerie crash
Apr 7, 2015
Alan Dron
Apr 7, 2015
Alan Dron
- The icing of engine power management sensors triggered the stall and fatal crash of Air Algerie flight AH5017 in northwest Africa last July 24, according to an investigation.
French air accident investigation agency BEA and Mali’s Commission d'Enquêtes Accidents et Incidents de l’Aviation Civile issued the update as the investigation proceeded. A final report is due in December.
Air Algerie Flight AH5017 from Ouagadougou, Burkina Faso, to Algiers was being operated by a Spanish wet-lease company Swiftair on behalf of the North African flag carrier with a Boeing MD-83.
It crashed in the Gossi region of northeastern Mali, killing all 110 passengers and six crew. The flight data recorder has yielded usable information, but the cockpit voice recorder is unreadable.
The aircraft, EC-LTV, took-off at 01:15 local and climbed uneventfully to its cruise attitude of 31,000 ft., with the crew making several heading changes to fly around a storm cell. The autopilot and the autothrottle were engaged.
The update stated that, about two minutes after leveling off at 31,000 ft., engine pressure ratio, the main parameter for engine power management, “became erroneous on the right-hand engine and, 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.”
The false EPR information transmitted to the autothrottle led it to reduce the engines’ thrust and the aircraft slowed. To compensate, the autopilot commanded an increase in pitch attitude to maintain height.
Speed dropped from 290 knots to 200 knots over a period of around five minutes and the angle of attack increased until the aircraft stalled.
About 20 seconds after the beginning of stall, the autopilot was disengaged. The aircraft rolled suddenly to the left until it reached a bank angle of 140 degrees, and a nose-down pitch of 80 degrees. The crew did not initiate any stall recovery maneuvers.
The investigators add that at least two similar events had occurred in the preceding two years—one involving another of Swiftair’s MD-83s—but with no serious consequences.
This background, the report stated, “should serve as the basis for future publication of corrective measures aimed at assisting crews in identifying and responding to similar situations.”
Further work is continuing, in particular to analyze the flight parameters to complete the scenario described above; possible crew reactions; and the training and follow-up of Swiftair crew.
