What happened
On March 11, 2004, at 17:20 UTC, a mid-air collision occurred approximately 1.5 NM west of the Château Arnoux Saint-Auban airfield. The incident involved a Socata Rallye MS 235 E (registration F-BXYS) acting as a tow plane and a Centrair C101A Pégase glider (registration F-TGDG).
The tow plane pilot had recently completed a glider release at 6,000 feet. Following the release, the pilot began a high-speed descent at 250 km/h, turning left toward the west. Simultaneously, the glider pilot was exiting a spiral turn to join the descent zone. As the glider pilot descended, they noted the tow plane directly ahead for approximately two seconds. Despite an immediate attempt to climb and turn left to avoid the aircraft, a collision occurred.
The impact caused significant damage to both aircraft: the F-BXYS lost its right wingtip, and the F-TGDG sustained a large tear on the leading edge of its left wing. Both pilots were able to land their respective aircraft safely at the airfield.
The investigation
The investigation focused on the visibility conditions, radio communications, and flight trajectories of both aircraft. Investigators examined the environmental conditions, noting that while the weather was clear, the sun was positioned low on the horizon, directly in the tow plane pilot's line of sight during the descent.
The investigation also reviewed the radio procedures used by both pilots. The tow plane pilot was using the airfield's self-information frequency (122.3 MHz), while the glider pilot was still monitoring a separate military operations frequency. Furthermore, the investigation looked into the flight paths, noting that the tow plane pilot was following a verbal instruction to fly west to avoid noise pollution, which deviated from the published traffic pattern on the VAC map.
Findings
- The high-speed descent of the tow plane at 250 km/h was inappropriate given the reduced visibility caused by the sun's position.
- The tow plane pilot's trajectory did not adhere to the published traffic pattern, leading the aircraft into the same circuit area used by gliders.
- Inappropriate radio usage by the glider pilot meant the two aircraft were not aware of each other's presence via radio contact.
- The glider's low detectability, particularly during a head-on approach, contributed to the late detection by the glider pilot.
- Low local traffic density on the day of the accident may have reduced the pilots' overall level of vigilance.