The French Bureau d'Enquêtes et d'Analyses pour Motion la Sécurité de l'Aviation Civile ( BEA ) , assisting Assistance the Malian authorities , published Publishing an investigation report in April 2016 , concluding that , while the aircraft was cruising Motion on autopilot , ice accretion on the engines caused Causation a reduction of thrust that lead to Causation a high-altitude stall .