Iran Aseman ATR 72-212 plane crash
The ATR-72-212 operated by Iran Aseman took off from Tehran, Iran, for a passenger flight to Yasuj, Iran. 60 passengers and 6 crewmembers were onboard. The plane disappeared from radar near the Zagroz Mountains. The wreckage was found 30 meters below the peak of the mountains south of Noqol. All the 66 people onboard were killed.
The crew was cleared to join the approach procedure to Yasuj. The crew did not indicate any emergency or abnormal situation on board. Communication with the aircraft was lost about 85 minutes after departure from Tehran. The aerodrome of Yasuj is surrounded by high mountains. Those mountains were covered by clouds at the time of the accident.
Flight data recorders analysis indicates that while approaching Yasuj, the aircraft levelled off at 15,000 ft on autopilot for 1 minute. Then the engines were reduced to idle, the speed reduced to 200 KIAS with the angle of attack increasing, the engines get slightly accelerated. The speed continued to decrease and reached 129 KIAS (minimum maneuvering speed 132 KIAS), the pitch reaches 15 degrees nose up, the engines accelerate. The altitude target is set to 14,000 ft and the aircraft begins to descend at about 600fpm. The speed further reduces to 117 KIAS, a stall warning activates, the crew disengages the autopilot, the aircraft rolls 20 degrees to the left, the pitch reduces to about 9 degrees nose down. Descending through 14200 ft at 137 KIAS the autopilot gets re-engaged, the aircraft rolls right by 12 degrees, the pitch increases to 5 degrees nose down. A GPWS warning "TERRAIN AHEAD! PULL UP!" activates, the autopilot is disengaged, the GPWS warning continues for 12 seconds until impact.
Iran investigation boards stated that the crew should have maintained 17,000 ft in accordance with the flight plan, however, descended the aircraft to 15,000 ft followed by a target altitude of 14,000 ft on the autopilot contrary to flight rules. In addition, while the crew was permitted to conduct the flight with the weather data available at the time of departure, the latest weather information provided by Yasuj Tower indicating clouds up to 15,000 ft prohibited the approach to Yasuj according to company procedures due to cloud cover present at the aerodrome, the crew should have diverted to Shiraz or Isfahan planned as alternate aerodromes.