About seventy minutes into the flight, the crew made a request to the Lorient approach controller to deviate from their route slightly to the west to Quiberon Bay.

[2]: 24  Both aircraft immediately fell to the water, killing all 14 passengers and crew on board the Beechcraft, as well as the sole occupant of the 177.

[2]: 53 In documentation published by the Aeronautical Information Service in 1997 and 1998 and probably used by the pilot of the Cessna, the use of a transponder while operating under visual flight rules could be interpreted as optional.

[2]: 36  As a result of the transponder being off, the Cessna was not depicted on the radar screen of the Lorient approach controller and its traffic information could not be relayed to the crew of the Beechcraft.

Had the Cessna's transponder not been turned off and the Beechcraft's TCAS not been uninstalled, a pilot with expected reaction time would likely have avoided the collision by about 300 feet.