On January 21, 1980, an Iran AirBoeing 727-86 was making a domestic flight from Mashad Airport to Tehran-Mehrabad Airport in Iran. At 1911h local time, the aircraft, registered as EP-IRD, collided with the Alborz Mountains, 29 kilometres (18 mi) north of Tehran, during its approach to Tehran-Mehrabad runway 29 in foggy and snowy weather conditions. All 8 crew members and 120 passengers died in the incident, and the plane was destroyed. At the time, Iran Air Flight 291 was the deadliest aircraft disaster in Iranian history.
Investigators concluded that the probable cause of the crash was believed to be an inoperable instrument landing system and ground radar. The head of Iran's Civil Aviation Authority and five other officials were charged with manslaughter as a result of the crash of Flight 291.