Investigation Summary
The flight was a leg of a long-distance cargo operation from the United Kingdom to Australia. The aircraft, G-AGRH, was a modified Avro Tudor IV known as a Super Trader IV, featuring an aft cargo door and an unpressurized cabin. After departing Ankara, the flight was supposed to follow an air corridor over Lake Van toward Tehran. However, the aircraft encountered significant navigational challenges. Investigators found that the crew was operating in instrument conditions and failed to account for strong winds that were more powerful than forecast. Additionally, the crew did not check the wind forecast at Van and was unable to obtain an accurate radio bearing at Muş. Environmental factors also played a role: sub-normal temperatures likely caused the altimeter to over-read, giving the crew a false sense of altitude. The lack of coordination between beacon contacts and flight calculations resulted in the aircraft drifting significantly north of its track, placing it directly in the path of Mount Süphan.
Final Conclusions
The official investigation concluded the primary cause was controlled flight into terrain resulting from navigational errors. The aircraft drifted off course due to strong winds that exceeded forecasts. Contributing factors included the failure to verify wind data at Van, the inability to secure a radio bearing at Muş, and altimeter errors caused by extremely low temperatures. The investigation also noted that contacts with navigational beacons were not sufficiently coordinated or controlled by the crew.
Video Analysis
Mysterious British Plane Crashes on Mount Süphan — A detailed look at the 1959 crash of the Avro Super Trader IV 'Zephyr' in Turkey, its secret cargo, and the subsequent RAF demolition mission.
If playback is blocked, the owner has disabled embedding — use the link above.
Systems & Failure Modes
Altimeter
Sub-normal temperatures at the time of the flight resulted in a high indicated altimeter reading, meaning the aircraft was lower than the instruments suggested.
Avro Super Trader IV Modification
A modified version of the Avro Tudor IV, fitted with an aft cargo door and operated as an unpressurized freighter.
Interesting Facts
- 01The aircraft was named 'Zephyr'.
- 02The aircraft was carrying top-secret equipment for the Woomera rocket range in Australia.
- 03The crash site was located near the Soviet-Armenian border, heightening Cold War security concerns.
- 04The wreckage was intentionally demolished by the RAF to prevent sensitive technology from being recovered by third parties.
- 05The aircraft was a modified Avro Tudor IV, designated as a Super Trader IV.
- 06All 12 individuals on board were killed; while often referred to as crew, some sources suggest they were a mix of crew and passengers associated with the mission.
Safety Actions & Advisories
Navigational Coordination Improvements
The investigation highlighted the need for better coordination and control of flight calculations and beacon contacts, particularly when operating in instrument conditions with unforecasted winds.
Known Controversies & Unanswered Questions
Nuclear Cargo Speculation
Reference ↗There has been unproven speculation that the aircraft was carrying nuclear warheads. Local rumors alleged villagers suffered radiation-related illnesses after visiting the site, though these claims lack official verification.