What happened
On August 19, 2018, at approximately 16:30, a Dynamic WT9 ultralight, identified as 68ADW, was performing a glider tow at the Colmar Houssen aerodrome. The tow formation included a Centrair 101A Pégase glider, registered F-CGOT.
Shortly after takeoff from the grass runway, the glider moved into a high position relative to the towplane. The pilot of the F-CGOT attempted to correct the altitude but subsequently deployed the airbrakes, which increased tension on the tow cable. The towplane pilot noticed the altitude discrepancy and observed the aircraft pitching down sharply. The WT9 lost altitude rapidly, and the tow cable eventually broke. The ultralight struck the ground near the threshold of runway 19, resulting in a post-impact fire. The one fatality was the pilot of the 68ADW. The pilot of the glider landed safely without injury.
The investigation
The BEA examined the wreckage of the 68ADW, noting that the propeller was still rotating upon impact and that the aircraft had a high vertical velocity at the moment of collision. The investigation focused on the tow cable, which had broken at the glider side near the knot. While the club had been using higher-rated fuses (750 daN) than the manufacturer's recommendation (300 daN) to prevent frequent breakage, the investigation looked at how this affected the separation of the aircraft.
Investigators also reviewed the glider's configuration, noting it used a central tow hook rather than a nose hook. The pilot's recent flight experience was also evaluated, as the glider pilot had a significant gap in regular flying prior to the accident.
Findings
- The primary cause of the accident was the glider moving into a high position, which destabilized the towplane.
- The deployment of airbrakes by the glider pilot increased cable tension, further destabilizing the WT9.
- The use of higher-rated fuses than those recommended by the manufacturer delayed the separation of the aircraft, preventing the towplane from recovering control.
- The glider's use of a central tow hook may have facilitated the transition into the high position.
- The glider pilot's recent lack of flying experience may have contributed to the delayed detection of the unusual flight position.