Investigation Summary
Flight 704 was originally scheduled to fly from Reykjavík to Vágar on September 23, 1970, but was repeatedly delayed by persistent fog at the destination. On September 25, the flight departed Reykjavík but was forced to divert to Bergen, Norway, after being unable to land at Vágar. The following morning, the aircraft departed Bergen at 08:22 to complete the journey. Upon arriving over the Faroe Islands at 10:20, the crew entered a holding pattern due to continued fog. At 10:52, the crew reported they were turning toward the 'MY' Non-Directional Beacon (NDB) to begin their final landing procedure. Three minutes later, they reported being inbound over the beacon and descending. However, the aircraft was not actually over the beacon; it was approximately one minute away from impact with the slopes of Mykines. The crash killed the captain and seven passengers, all of whom were seated on the left side of the fuselage. In a remarkable feat of survival, three passengers hiked for an hour through difficult terrain to reach Mykines village to summon help.
Final Conclusions
The accident was classified as a Controlled Flight Into Terrain (CFIT). The primary cause was the initiation of the descent procedure from a position other than the 'MY' NDB. This navigational error was attributed to the aircraft's weather radar T/R unit, which had an instability between 315 KHz and 339 KHz, interfering with the ADF equipment tuned to 337 KHz. This provided the flight crew with a false indication that they had passed the beacon. The aircraft struck the mountain at an altitude of 1,500 feet while in a controlled descent.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
Automatic Direction Finder (ADF)
A radio-navigation instrument that automatically displays the relative bearing to a ground-based radio station (NDB). In this accident, it provided an erroneous 'station passage' indication.
Weather Radar
Used to detect precipitation and turbulence; investigators concluded this system likely caused electromagnetic interference with the ADF.
MY Non-Directional Beacon (NDB)
The primary navigational aid used for the approach to Vágar Airport, which the crew believed they had passed when they began their descent.
Interesting Facts
- 01The aircraft was jointly owned by Flugfélag Íslands and Scandinavian Airlines (SAS).
- 02All eight fatalities occurred among occupants seated on the left side of the aircraft.
- 03The flight had been delayed for three days due to poor weather conditions in the Faroe Islands.
- 04The crash site was near the highest point of the island of Mykines.
- 0526 people survived the impact, though some sustained serious injuries.
Safety Actions & Advisories
ADF and Radar Interference Warning
The investigation highlighted the risk of electromagnetic interference between the aircraft's weather radar T/R unit and the Automatic Direction Finder (ADF) equipment, particularly when tuned to frequencies near the radar's instability range (315-339 KHz).