What happened
On June 23, 2004, at approximately 16:47 UTC, a Dynali Chickinox Kot Kot ultralight, registration 83-JV, was conducting a training flight at the Cuers Pierrefeu aerodrome. The flight was intended to help the owner-pilot obtain the necessary training for passenger carrying privileges. After completing an initial circuit, the pilot announced a low-level circuit. During a turn, the crew decided to shorten the circuit to allow an aircraft on the ground to proceed to the runway holding point. During this maneuver, the aircraft entered a steep dive. An instructor on the ground observed the aircraft in a heavy pitch-down attitude with significant bank, noting that no recovery attempt was visible before the impact.
The investigation
The investigation focused on the aircraft's mechanical condition and the flight controls. Investigators examined the wreckage and found no evidence of engine failure or structural failure prior to impact; the engine was producing low power at the time of the crash, and the propeller remained intact. The investigation also scrutinized the aircraft's control surfaces. It was discovered that the 83-JV was equipped with older-model return springs on the elevator control cables, which were weaker than the standard recommended by the manufacturer since late 1992. Additionally, the aircraft featured an unauthorized modification to the elevator trim tabs, where the standard dual-tab setup had been replaced by a single, larger tab on the left side only. The investigation also noted that the pilot performed his own maintenance and that the aircraft's previous sale documentation did not disclose these deviations from the manufacturer's recommended configuration.
Findings
- The aircraft experienced a loss of control not caused by mechanical failure.
- The primary cause was likely the crew's lack of familiarity with the specific aerodynamic characteristics of the Chickinox Kot Kot 3-axis "double surface" model, specifically the risk of the elevator losing effectiveness at low speeds and reduced power.
- The use of non-compliant, weaker return springs likely contributed to the inability to maintain control.
- The decision to reduce engine power to shorten the circuit contributed to the loss of elevator effectiveness due to lack of airflow over the control surfaces.
- The aircraft was equipped with unauthorized modifications to the elevator trim tabs.