What happened
On March 15, 2012, at 13:40 local time, a Robin DR 400-120, registration F-GXGB, was performing a takeoff roll on the unpaved runway 05R at Sarreguemines Neunkirch aerodrome. During the takeoff roll, at a speed between 100 and 110 km/h, the student pilot attempted to rotate the aircraft by pulling back on the elevator control, but the aircraft failed to respond. The instructor then took control and applied full elevator deflection, but the aircraft continued to accelerate without reacting to the pitch input.
In an attempt to abort the takeoff, the instructor applied the brakes. The aircraft veered longitudinally off the runway, crossed a ditch, and the nose gear collapsed. The aircraft came to a stop 160 meters beyond the end of the runway. Shortly after the aircraft stopped, flames were observed near the front right of the engine. Both occupants evacuated the aircraft using the emergency handle. Approximately one minute after evacuation, an explosion occurred, and the aircraft was completely consumed by fire. There were no fatalities.
The investigation
The investigation focused on the continuity of the elevator control system. Examination of the wreckage revealed that the continuity of the elevator control chain was interrupted at the connection between the cables and the elevator horn. While the lower cable connection showed evidence of molten metal, indicating it was intact prior to the fire, the upper cable connection lacked such deposits. This suggested that the horn had likely detached from its attachment point before the fire began.
Investigators also noted that during a period of intense cold in February 2012, temperatures had dropped as low as -16 °C. An instructor from the aircraft's home base had previously reported significant resistance in the flight controls during this cold period and had requested an adjustment to the control tension, though this request had not been implemented.
Findings
- The accident was caused by the failure of the upper end of the elevator horn during the takeoff phase.
- A recent period of extreme cold contributed to increased tension in the elevator control cables due to thermal contraction.
- This heightened tension likely caused premature wear and subsequent failure of the aluminum alloy elevator horn.