Accident
On a scheduled flight from Tehran-Imam Khomeiny Airport to Yerevan, a three-engine aircraft departed at 1117 local time with 158 passengers and 10 crew members. Sixteen minutes after takeoff, while cruising over Qazvin at flight level 340 (FL340), the aircraft suddenly changed its heading to 270 degrees and entered a rapid descent, losing 20,000 feet in 90 seconds. The aircraft descended in a near vertical attitude and crashed in an open field, creating a large crater. The aircraft disintegrated on impact, and all 168 occupants were killed.
Investigation
The official investigation found the probable cause to be a failure of the first stage of the high compressor disk on the left engine while the aircraft was at FL340. The failure was attributed to fatigue cracks. Debris from the failed disk punctured the engine nacelle and severed several hydraulic and fuel lines, rendering all control systems unserviceable. A large fire spread on the left side of the aircraft, leading to an uncontrolled descent that continued until impact.