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Last updated: 8 December 2021
Datum:vrijdag 27 oktober 1972
Type:Silhouette image of generic VISC model; specific model in this crash may look slightly different
Vickers 724 Viscount
Luchtvaartmaatschappij:Air Inter
Registratie: F-BMCH
Constructienummer: 50
Bouwjaar: 1955
Aantal vlieguren:31413
Aantal vluchten:26330
Motoren: 4 Rolls-Royce Dart 506
Bemanning:slachtoffers: 5 / inzittenden: 5
Passagiers:slachtoffers: 55 / inzittenden: 63
Totaal:slachtoffers: 60 / inzittenden: 68
Schade: Vernield
Gevolgen: Written off (damaged beyond repair)
Plaats:4 km (2.5 mijl) W of Noirétable (   Frankrijk)
Fase: Kruisvlucht (ENR)
Soort vlucht:Binnenlandse lijnvlucht
Vliegveld van vertrek:Lyon-Bron Airport (LYN/LFLY), Frankrijk
Vliegveld van aankomst:Clermont-Ferrand-Aulnat Airport (CFE/LFLC), Frankrijk
Air Inter flight 696 departed Lyon for a night time flight to Clermont-Ferrand. It was raining in the area of Clermont-Ferrand, the visibility was around 5 miles with a low 4/8 ceiling at 2300 feet and an overcast at 8000 feet. Near Clermont-Ferrand, the crew had to fly a holding pattern before being cleared to descend to 3600 feet. Then the airplane's radio compass shifted 180-degrees, probably because electrical discharges in the rainfall blocked the signals of the Clermont-Ferrand (CF) NDB. The crew initiated their descent too early and the Viscount collided with a mountain (Pic du Picon) at 1000 feet, 44 km east of the airport.

Probable Cause:

Cause (translated from French):
The accident is a direct result of a collision with the terrain, which occurred at night in stormy conditions near a cold front, while the aircraft was following an apparently normal approach procedure, but shifted eastward by about 30 km.
The origin of this accident reveals two anomalies.
The first is that the crew was convinced that they were actually over CF when in fact the beacon was more than 30 km away. It seems to be explained only by a strong rotation of the direction finder, whose aberrant character could not be detected by the crew. Still it is necessary to admit moreover that the indications of the direction finder afterwards presented coherent variations with the successive positions of the plane during the double circuit of descent and with the second overflight of the CF beacon.
The second anomaly is characterized by the announcement of the beacon overflight by the aircraft, more than three minutes ahead of an estimated eight minutes. This difference may have been overlooked by the crew because of their confidence in the radio compass indication. One can also think that this difference went unnoticed by the crew either because they forgot to check the time or because of a reading error, as the crew had to face a difficult piloting due to turbulence and the presence of a training pilot could also have been a factor of concern and distraction at that time.
The work of the commission having made it possible to rule out the hypothesis of a pirate transmitter, the erroneous indication of the radio compass could have resulted either from a defect in the installation of the on-board antenna system associated with certain conditions of the electric field, or more probably from very localized precipitation which accompanied the cold front in the zone of the accident and which could have constituted a kind of transmitter (series of microdischarges) sufficiently powerful to be, during this phase of flight, detected by the aircraft's radio compass by suffocating the CF field.
The interception of the ILS localizer probably strengthened the crew's conviction.
In addition, it is not impossible that the light halo of the city of Thiers, perhaps visible at certain times, may have been an additional motivating factor.
Although the instructor pilot had the reputation of attaching great importance to a cross-checking of positions, which was possible in particular by the radial of Moulins, it seems that the crew did not do anything about it.
The commission, in definite, admits the possibility of an aberrant indication of a radio compass, but cannot explain the reasons that prevented the crew from correctly controlling the point from which the descent was started and continued.

Accident investigation:
Investigating agency: BEA
Status: Investigation completed
Duration: 1 year
Accident number: Report f-ch721027
Download report: Final report


photo of Vickers-724-Viscount-F-BMCH
accident date: 27-10-1972
type: Vickers 724 Viscount
registration: F-BMCH

Deze kaart geeft het vliegveld van vetrek weer en de geplande bestemming van de vlucht. De lijn tussen de vliegvelden geeft niet de exacte vliegroute weer.
De afstand tussen Lyon-Bron Airport en Clermont-Ferrand-Aulnat Airport bedraagt 137 km (86 miles).
Accident location: Approximate; accuracy within a few kilometers.

This information is not presented as the Flight Safety Foundation or the Aviation Safety Network’s opinion as to the cause of the accident. It is preliminary and is based on the facts as they are known at this time.
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Vickers Viscount

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