What happened
On Monday, August 11, 1997, at 14:15, a Robin HR 200-120 B, registration F-GORV, departed from Annecy for a local flight over the lake. Approximately five minutes into the flight, while cruising at 3,500 feet, the pilot experienced a sudden and significant drop in engine speed, with RPM falling from 2,700 to 1,500. Suspecting fuel contamination, the pilot decided to return to the departure airfield.
In an attempt to maintain flight for as long as possible, the pilot pulled back on the control column. This maneuver caused the aircraft to approach its aerodynamic limits; the pilot noted that he would pull the stick back until the stall warning sounded, then release it to regain airspeed. During this sequence, the aircraft struck the roof of a school and subsequently crashed into a street below, striking parked vehicles. The impact occurred at an altitude of approximately 1,500 feet, roughly 750 meters from the threshold of runway 04. The accident resulted in two injuries (the pilot and one passenger) and caused heavy damage to the aircraft.
The investigation
The investigation focused on the cause of the engine power loss and the pilot's subsequent flight maneuvers. A visual inspection of the engine at the accident site revealed the presence of water within the carburetor's fuel pump. Additionally, investigators analyzed the aircraft's aerodynamic performance, specifically regarding the relationship between airspeed, lift, and drag during an engine-out glide.
Findings
- The primary cause of the engine malfunction was the presence of water in the carburetor fuel pump.
- The pilot's attempt to extend the glide distance by pulling back on the controls led to an unsafe flight regime. By attempting to fly at speeds near the stall limit, the pilot failed to maintain the maximum glide speed (best glide speed), which is essential for maximizing distance during an engine failure.
- For the Robin HR 200-120 B at maximum takeoff weight, the maximum glide speed is 120 km/h, whereas the stall speed is 110 km/h (or 100 km/h with 10° flaps). The pilot's maneuvering significantly reduced the aircraft's ability to reach the airfield.