On 18 February 2018, contact was lost with an ATR72-500 approaching Yasouj and two days later the wreckage of the aircraft was located in mountainous terrain with no sign of survivors. The flight recorders were eventually recovered and their data helped attribute the accident to descent below the designated minimum safe altitude followed by an encounter with severe mountain wave conditions which led to the crew losing control and a terrain impact which destroyed the aircraft and killed all its occupants. An apparently widespread failure to recognise the potential risk of severe mountain wave encounters was also found.