Investigation Summary
The accident occurred as the crew was attempting a truncated instrument approach to runway 06. During the descent, the captain engaged in a private conversation with the air traffic controller regarding the upcoming Christmas holidays, violating the principles of a sterile cockpit. This distraction occurred while the aircraft was navigating through darkness and fog. The investigation revealed that the aircraft's ADF (Automatic Direction Finder) number 2 was likely tuned to 100 kHz in error, causing it to receive signals from a longwave transmitter in Lahti, Finland, rather than the intended local beacon. Furthermore, the ILS system for runway 06 was known to produce false glideslope signals in the area of the crash site, which may have misled the crew into believing they were on the correct path. The rescue operation was hampered by the remote, wooded terrain and incorrect search coordinates initially provided to the police. While seven people initially survived the impact, two succumbed to their injuries before or during the rescue process, resulting in a six and a half hour delay before the wreckage and the five final survivors were located.
Final Conclusions
The investigation commission concluded the primary cause was a navigational error that occurred before the aircraft descended below 1,100 meters (3,500 feet). The crew failed to recognize that they were more than 4 nautical miles off course and 1,510 feet below the glide path; this deviation became fatal during the final 13 seconds of flight. Contributing factors included the captain's lack of rest (the report stated he was not as rested as he could have been according to regulations), the unauthorized radio chatter, and the lack of radar monitoring by air traffic control, who had the equipment to see the deviation but no instructions to intervene. Technical factors included the interference between ILS beacons for different runways and the susceptibility of the aircraft's marker beacon receiver to false signals when set to 'HIGH'. Additionally, the control tower bearing indicator had been moved from its fixed position in the control desk, which reduced the possibility of random directional control checks by the controller.
Photographic Evidence (1)
Video Analysis
The Pilot's Nightmare From Hell | The Bizarre Case of Braathens Flight 239 — A detailed look at the Asker Disaster, exploring the navigational errors, pilot fatigue, and the tragic sequence of events that led to Norway's deadliest civil aviation accident at the time.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Crew Experience
Captain
Employed by Braathens for 16 years; investigation noted he was not as rested as regulations required.
First Officer
Nine years of experience with Braathens.
Systems & Failure Modes
Instrument Landing System (ILS)
The system for runway 06 provided usable but false glideslope signals in the area where the aircraft crashed.
Automatic Direction Finder (ADF)
One ADF unit was erroneously tuned to 100 kHz, leading to incorrect navigational bearings.
Outer Marker Beacon
The receiver could provide false passage signals if the sensitivity switch was set to 'HIGH'.
Interesting Facts
- 01The aircraft, LN-SUY, was the first Fokker F28 to enter revenue service in 1969.
- 02The aircraft was named 'Sverre Sigurdsson'.
- 03The passenger count of 42 included four infants.
- 04The crash was the deadliest civil aviation accident in mainland Norway.
- 05Five passengers survived the impact and the subsequent fire, while 40 occupants perished.
- 06The investigation found the radio compass was receiving signals from Lahti, Finland, due to an incorrect frequency setting.
Safety Actions & Advisories
Navigational Redundancy
The commission recommended that airlines enforce routines requiring multiple independent systems to be used for determining position and bearing.
ATC Monitoring Procedures
Recommendations were made to update air traffic control instructions so that radar could be used to actively alert pilots if they deviate from their assigned path.
Infrastructure Improvements
The installation of an additional radio beacon in Drammen was recommended to better aid the approach to runway 06 at Fornebu.
Known Controversies & Unanswered Questions
Allegations of Pilot Intoxication
While the official report only stated the captain was 'not as rested as he could have been', persistent reports and rumors suggested he had been seen consuming alcohol in the early hours of the morning on the day of the accident. The investigation did not formally cite intoxication as a cause.