Isfahan

The accident was happened due to many chains of considered causes but the “Human Factor” had main roll for the conclusion of the scenario. The Cockpit Crew action which has caused dangerous conditions for the flight is considered as main cause. Based on provided evidences, the errors of cockpit crew were as follows:
- Continuing to the Yasouj airport for landing against Operation manual of the Company, due to low altitude ceiling of the cloud and related cloud mass. They should divert to alternate airport,
- Descending to unauthorized altitude below minimum of the route and MSA,
- Lack of enough CRM during flight,
- Failure to complete the stall recovery (flap setting, max RPM),
- Inappropriate use of Autopilot after Stall condition,
- Inadequate anticipation for bad weather based on OM (Clouds, Turbulence, and Icing ...),
- Quick action to switch off anti-ice system and AOA,
- Failure to follow the Check lists and standard call out by both pilots.
Contributing Factors:
The contributive factors to this accident include but are not limited to the following:
- The airline was not capable to detect systematic defectives about :
- Effectiveness of crew training about Meteorology, OM, SOP,
- Enough operational supervision on pilot behaviors,
- The lack of SIGMET about Mountain Wave or Severe Mountain wave,
- Unclear procedure for stall recovery in FCOM,
- Lack of warning in aircraft manuals by manufacturer for flight crew awareness about mountain wave.
- Lack of APM System to alert crew about performance degradation.
Other Deficiencies and Short Comes:
In the process of the accident investigation, some detailed deficiencies and short comes were found and should be considered as latent conditions by related authorities:
- AD accomplishment and related monitoring,
- Sanction on aviation industries and effect on Flight safety,
- Non-standard communication between ATC and crew,
- Unclear definition of the Fully Qualified Pilot and qualified copilot in Aircrew regulation.
- Weather forecast (TAF) in the airports based on annex 3 procedure in the Civil Aviation Organization for approving alternative method of compliance for aircraft AD,s
- Search and rescue Coordination with local authorities for aviation accidents,
- Time setting of aircraft flight data recording(FDR) either by technician or pilots.

Controlled flight into terrain after the pilots failed to use properly the GPS system installed in the cockpit.

For unknown reasons, both engines lost power simultaneously, causing the aircraft to enter an uncontrolled descent.

The pilot was unexpectedly confronted with severe carburetor icing conditions. A loss of engine power resulting from this impelled him to descend through the cloud layer when possibly the icing conditions became considerably worse, thus rendering a quick melting of the carburetor ice problematic. His already serious situation was intensified due to breaking cloud over mountainous terrain under conditions of bad visibility. In an effort to avoid the mountain barriers confronting him, he endeavored to fly through a narrow gorge and a visible gap at the top. He, however, to a still greatly diminished power from the persistent effects of carburetor icing, together with the most imposing turbulence and downdraught effects that he would undoubtedly encounter in the crest area, his attempt failed. Unfortunately, the protruding rock formation which he first hit presented a further great obstruction at the most critical point of his passage.