Investigation Summary
The flight took place against a backdrop of industrial unrest. Iranian air traffic controllers had been on strike, causing widespread cancellations, and had only resumed work at 16:00 local time, less than two hours before Flight 291 departed Mashhad. During the approach to Tehran, the crew was operating in challenging conditions including night, fog, and snow. Navigational confusion arose when the air traffic controller instructed the crew to take a 360 degree heading to reach the Varamin non-directional beacon. The aircraft drifted 17 miles off course to the north. Although the first officer noted that the VORTAC was providing incorrect radial information, the captain did not take corrective action. The lack of functional ground radar meant controllers could not see the deviation, and the inoperative ILS deprived the crew of a precision approach path.
Final Conclusions
The investigation attributed the crash to Controlled Flight Into Terrain (CFIT) caused by a combination of human error and infrastructure failure. Primary factors included the crew's deviation from the approved ATS route and the unauthorized 360 degree turn. Contributing to the disaster were the inoperative ILS and ground radar systems at Mehrabad Airport, as well as the adverse weather conditions. The systemic failure to maintain operational safety equipment led to the prosecution of several high ranking aviation officials.
Photographic Evidence (1)
Video Analysis
No video analysis linked for this case file yet.
Systems & Failure Modes
Instrument Landing System (ILS)
A precision radio navigation system that provides short-range guidance to aircraft to allow them to approach a runway at night or in bad weather; it was inoperative at the time.
VORTAC
A radio-based navigation aid that the first officer identified as providing incorrect or conflicting radial information during the descent.
Ground Radar
Airport surveillance radar used by controllers to monitor aircraft positions; its failure prevented ATC from noticing the flight's 17-mile deviation.
Interesting Facts
- 01The crash was the deadliest aviation accident in Iranian history at the time, a record it held until the downing of Iran Air Flight 655 in 1988.
- 02The aircraft was a Boeing 727-100 series (727-86) built in 1968.
- 03The Instrument Landing System (ILS) and ground radar at Mehrabad Airport were both inoperable during the approach.
- 04The aircraft was 17 miles north of its intended course at the time of the accident.
- 05The head of Iran's Civil Aviation Authority and five other officials were later charged with manslaughter.
Safety Actions & Advisories
Infrastructure Upgrades
The disaster highlighted the critical need for reliable navigation aids, leading to investments in functional ILS and ground radar systems across Iranian airports.
Enhanced Crew Training
Reforms were introduced to improve training for flight crews and air traffic controllers, emphasizing strict adherence to standard operating procedures and ATS routes.