What happened
On May 21, 2015, a DR400-140B, registration F-GBUP, departed from Arras aerodrome for a training flight involving an instructor, a pilot, and a passenger. During the initial climb following a touch-and-go maneuver, the engine experienced power loss and eventually stopped.
Following the engine failure, the aircraft entered a left-hand turn at a low altitude. The instructor took control of the aircraft and attempted an emergency landing on a road perpendicular to the runway. During this maneuver, the aircraft entered a stall and struck the ground with a high bank angle and a nose-down attitude. The impact caused the aircraft to slide approximately 70 meters before coming to rest on its back. A post-impact fire destroyed the wreckage. The accident resulted in two fatalities (the instructor and the passenger) and one injury (the pilot).
The investigation
The BEA examined the wreckage, the engine, and the flight history of the aircraft. Investigators noted that the engine, a Lycoming O-320-D2A, was showing significantly lower fuel consumption than manufacturer specifications. While the engine had recently undergone a major overhaul and a 100-hour inspection, data indicated an average consumption of approximately 24 l/h, whereas the manufacturer's documentation suggests much higher rates (up to 38 l/h at 75% power).
An examination of the engine revealed an anomaly involving a cylinder tie bar, though investigators could not establish a direct link between this component's displacement and the engine failure. Testing on a test bench demonstrated that running the engine with an excessively lean mixture could lead to significantly reduced fuel consumption, which might go unnoticed by operators.
Findings
- The primary cause of the accident was a loss of control during a low-speed turn at low altitude following an engine failure during the initial climb.
- The aircraft likely experienced an asymmetric stall during the maneuver.
- The instructor's decision to target the road rather than the adjacent open field—which was suitable for an emergency landing—may have been influenced by a desire to avoid damage to the aircraft from the crops.
- Contributing factors included the lack of a pre-takeoff briefing and the instructor's extensive experience, which may have influenced his decision-making during the emergency.
- The unusually low fuel consumption of the engine was noted as a significant discrepancy that could mislead an operator regarding engine health.