What happened
On September 7, 2014, a privately owned Stoddard-Hamilton Glasair II FT, registration HB-YGL, was performing a local flight from the Talmont Saint-Hilaire airfield in France. The aircraft was accompanied by one passenger. Shortly after rotation on runway 03, the engine experienced several loud detonations and a significant loss of power.
In an attempt to manage the failure, the pilot adjusted the aircraft's pitch; however, the aircraft entered an asymmetric stall to the right. The aircraft subsequently collided with a cornfield approximately 60 meters from the runway threshold. The impact resulted in two serious injuries and the destruction of the aircraft.
The investigation
Investigators examined the wreckage and the propulsion system to identify the cause of the power loss. While the engine block and fuel system showed no signs of internal failure or contamination, evidence of high-temperature operation was found, including white discoloration inside the cylinder chambers and exhaust pipes. Additionally, a resistance irregularity was noted in the left magneto coil, though testing could not replicate a failure during flight conditions.
Witnesses at the airfield reported hearing three heavy engine detonations over a ten-second period. They also observed the aircraft banking right and losing altitude before the impact. The investigation also reviewed the pilot's recent flight experience and the aircraft's performance characteristics, noting that the Glasair II has a high wing loading, which results in a high sink rate during engine-out scenarios.
Findings
- The engine was operating at temperatures above normal, likely due to a lean fuel mixture, which can trigger detonations and power loss.
- A potential malfunction in the left magneto may have contributed to the engine instability.
- The pilot's pitch adjustment was not sufficiently immediate or aggressive to prevent the aircraft from decelerating and entering an asymmetric stall.
- The pilot's attention was likely diverted to monitoring engine parameters to diagnose the power loss, leading to insufficient flight path control.
- The aircraft's lack of a stall warning system may have prevented the pilot from detecting the onset of the stall in time to recover at such a low altitude.