Investigation Summary
The investigation focused on two primary anomalies: the false radio compass (ADF) indication and the crew's failure to cross-check their position. The radio compass likely suffered a 180 degree shift due to 'static' or micro-discharges from a localized cold front, which effectively drowned out the signal from the Clermont-Ferrand (CF) beacon. This led the crew to report passing the beacon three minutes earlier than their own estimates. Despite the presence of an instructor pilot known for rigorous cross-checking, the crew did not use the Moulins VOR radial to verify their position. The crew's conviction was further reinforced by the accidental interception of a false ILS localizer signal and possibly the visual sighting of lights from the town of Thiers, which they may have mistaken for Clermont-Ferrand.
Final Conclusions
The BEA concluded the accident was a Controlled Flight Into Terrain (CFIT) resulting from a navigation error. The primary cause was the crew's reliance on an aberrant radio compass indication that was likely influenced by atmospheric electrical activity. Contributing factors included the crew's failure to detect a significant timing discrepancy (arriving three minutes early) and the lack of position cross-checking during a high-workload approach in turbulent, stormy conditions.
Video Analysis
Air Inter Flight 696 Aftermath Footage | 27 October 1972 Noirétable, France — Historical aftermath footage and accident description of the Air Inter Flight 696 crash near Noirétable, France.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Crew Experience
Captain
Copilot
Systems & Failure Modes
Radio Compass (ADF)
The primary navigation tool used for the approach, which provided an aberrant 180-degree shift due to weather interference.
ILS Localizer
The crew believed they had intercepted the ILS, which reinforced their false belief that they were on the correct approach path.
NDB (Non-Directional Beacon)
The ground-based Clermont-Ferrand (CF) transmitter whose signal was 'suffocated' by localized precipitation and micro-discharges.
Interesting Facts
- 01The aircraft was 44 km east of the airport and approximately 30 km east of its intended track at the time of the crash.
- 02Atmospheric electrical discharges from a cold front likely caused the radio compass to point toward the storm rather than the NDB.
- 03The crew reported passing the beacon at 19:17, despite an earlier estimate that they would not reach it until 19:20.
- 04The crash site was located on the border of the Loire and Puy-de-Dôme departments.
- 05The aircraft was a Vickers Viscount 724 manufactured in 1955.
Safety Actions & Advisories
Position Cross-Checking Requirements
The investigation highlighted the critical need for crews to cross-check NDB/ADF indications with other available navigation aids, such as VOR radials, especially in stormy conditions.