What happened
On September 8, 2009, at approximately 12:40 UTC, a mid-air collision occurred over Saint-Martin-de-Brloéthencourt, France, involving two aircraft operating under Visual Flight Rules (VFR). The first aircraft, a Reims Aviation F 172 with registration F-BXIU, was conducting a local instructional flight from Toussus-le-Noble. The aircraft was performing various maneuverability exercises at a relatively constant altitude.
The second aircraft, a Rockwell Commander 114 with registration G-DANT, was engaged in a cross-country flight from Lognes toward Dinard. The pilot was maintaining a steady course of 260 degrees at 1,500 feet.
During the flight, the F-BXIU performed a right turn of more than 180 degrees before stabilizing on a northerly heading. During this sequence, the two aircraft collided. The impact caused a portion of the F-BXIU's right wing to detach. The F-BXIU subsequently struck the ground in an inverted position, causing a fire and resulting in two fatalities (the student pilot and the instructor).
The pilot of the G-DANT managed to maintain control of the aircraft despite significant damage to the left wing. After declaring an emergency and reporting that he had struck an aircraft, the pilot performed an emergency landing in a field near Boinville-le-Gaillard. The pilot of the G-DANT was uninjured, while the passenger sustained minor injuries.
The investigation
The BEA investigation focused on the flight trajectories, the visibility of the aircraft to air traffic services, and the technical state of the aircraft. Investigators examined radar data, which showed the flight paths of both aircraft. The investigation also reviewed the transponder settings and the functionality of the Flight Information Service (FIS) provided by Paris Info.
It was established that the G-DANT was visible on the radar screen because it was using transponder code 7010. However, the F-BXI0 was using code 7000 and was not visible to the FIS controller. Furthermore, the G-DANT was experiencing a failure of its Mode C altitude reporting capability.
Findings
- The collision was caused by the failure to maintain adequate separation through the application of the "see and avoid" principle.
- The F-BXIU was not visible on the radar screen of the Flight Information Service because it was using transponder code 7000, a setting that controllers typically do not activate to avoid screen saturation.
- The G-DANT was unable to provide altitude information to air traffic services due to a malfunctioning Mode C transponder.
- The pilot of the G-DANT was flying with the sun at a disadvantageous angle (backlit), which may have hindered visual acquisition of the other aircraft.
- The F-BXIU was performing maneuvers that changed its heading significantly just prior to the impact.