What happened
On Friday, April 11, 2003, a single-seat Yakovlev Yak 3, registration F-AZLY, was performing a local flight at Caen-Carpiquet Airport. This was the owner's first flight of the season in this specific aircraft. During the pre-flight inspection, the pilot noted no anomalies. However, shortly after takeoff, the pilot discovered that the landing gear failed to lock in the retracted position. Following the flight manual, the pilot utilized the emergency air reserve to extend and lock the gear, subsequently deciding to terminate the flight early.
Believing there was sufficient pressure remaining in the emergency reservoir, the pilot attempted to extend the underside flaps. Following this action, the flaps began to flap uncontrollably in the relative wind, causing the aircraft to become unstable and heavy on the controls. During the approach to runway 13, the pilot misjudged the flare height and initiated a go-around. During this maneuver, the left wing struck the runway, causing the aircraft to yaw left. The propeller struck the ground, and a blade impacted the concrete runway edge. The resulting impact caused the reduction gear to disintegrate, and the propeller was thrown several meters from the aircraft. The aircraft then veered off the runway and came to a stop on its landing gear, at which point an engine fire ignited. The pilot escaped the aircraft without injury.
The investigation
The investigation focused on the pneumatic system responsible for the landing gear and underside flaps. This system consists of a primary circuit and a small compressed air reservoir for emergency use. Examination of the F-AZLY revealed a leak caused by a faulty seal within the landing gear control mechanism. This leak had occurred during the initial gear retraction attempt, depleting the pressure in the emergency reservoir.
Findings
- The pilot's misjudgment of the flare height during the go-around contributed to the wing strike.
- A faulty seal in the pneumatic circuit caused a loss of pressure in the emergency reservoir.
- While the remaining pressure was sufficient to lock the landing gear in the down position, it was insufficient to maintain the extended position of the underside flaps.
- The uncontrolled movement of the flaps in the airflow created significant aerodynamic instability and made the aircraft difficult to control at low speeds and during power changes.