What happened
On June 14, 2011, a Piper J3 C65, registration F-BHHQ, departed from the Serres-La Bâtie aerodrome for a private local flight carrying one passenger. During the initial climb, the pilot executed a left turn toward the Grand Buech valley to take advantage of available updrafts. However, at approximately 200 feet, the aircraft began to descend.
In an attempt to regain altitude, the pilot performed a turn to return to the original heading. During this maneuver, the pilot encountered a row of poplar trees and applied maximum power while pitching the aircraft up. Despite the full throttle setting, the aircraft failed to gain altitude. Realizing the aircraft was too low to safely rejoin the base leg for a landing on runway 36, the pilot opted to land in a nearby field of tall grass facing south. During the landing roll, the aircraft' landing gear collapsed after striking an irrigation ditch that was not visible from the cockpit. The aircraft sustained heavy damage.
The investigation
The investigation focused on the aircraft's performance capabilities and the environmental conditions at the time of the accident. Investigators noted that the weather featured a north wind of 5 to 10 knots and a temperature of 27 °C, conditions that likely promoted vertical thermal movements.
The investigation also examined the engine configuration. The aircraft was equipped with a 65 hp engine and a fixed-pitch propeller (specifically a "large pitch" propeller rather than a "small pitch" version). The pilot indicated that during the high-pitch, low-speed climb attempt at maximum power, the engine likely transitioned into a second regime, which prevented the aircraft from maintaining or increasing its altitude.
Findings
- The primary cause of the accident was the pilot's optimistic estimation of the aircraft's performance relative to the prevailing atmospheric conditions.
- The decision to perform an initial turn into an area of descending currents contributed to the loss of altitude.
- The use of a large-pitch propeller hindered the aircraft's ability to maintain climb performance during the low-speed maneuver.