Accident
An Avro York aircraft operating a freight flight from Beirut to Tehran via Kuwait crashed shortly after takeoff from Mehrabad Airport. The flight had departed from Kuwait and was en route to Tehran when the accident occurred. On the Kuwait-Tehran leg, a check pilot was examining the pilot in command and co-pilot for renewal of their licenses. Shortly after takeoff from Mehrabad, while climbing, the airplane went out of control and crashed in a huge explosion 11 kilometers southeast of Karaj, west of Tehran. The aircraft was completely destroyed upon impact, and all four crew members were killed.
Investigation
Investigators examined the wreckage to determine the sequence of events leading to the loss of control. The position of the propellers at the time of impact provided key evidence. Mehrabad Airport, from which the flight had just departed, has an elevation of 3,900 feet. The aircraft was fully loaded at the time of the accident.
Probable Cause
The official findings stated: "The position of the propellers at the time of impact would indicate that, at a time when the no. 4 engine power was off, an emergency condition developed which necessitated the feathering of no. 3 engine and the unfeathering of no. 4. Alternatively, a loss of power on the starboard engines could have occurred from an erroneous manipulation of the feathering switches during the course of this assumed crew checking exercise. In view of the fact that the fully loaded aircraft was flying at a low altitude after taking off from Mehrabad Airport which has an elevation of 3900 feet, it is evident that at the aircraft would not have sufficient altitude for the pilot to take effective recovery action and so avoid a crash resulting from the above mentioned loss-of-power conditions."