What happened
On June 20, 2012, an Aquila AT01, registration F-GVAQ, was performing a flight training exercise at the Brest Bretagne aerodrome. The flight, conducted by an instructor and a student pilot, involved a simulated engine failure maneuver known as an "L-shaped" landing. During the downwind leg, the aircraft encountered increasing rainfall, which significantly reduced visibility and caused condensation to cover the canopy.
As the instructor took control to demonstrate the maneuver, the engine power was reduced. Upon extending the flaps during the final approach, the aircraft's flight path became destabilized, causing it to sink abruptly. The aircraft touched down approximately 27 meters before the runway threshold in a grassy area. The impact with the edge of the runway caused the nose landing gear to collapse. The aircraft subsequently regained altitude, and the instructor applied power to complete the landing approximately 250 meters beyond the threshold.
The investigation
The investigation focused on the aerodynamic performance of the aircraft under heavy rain and the decision-making process of the crew. Investigators examined the aircraft's maintenance history, noting that the wing surfaces were slightly matte in certain areas, which can affect the performance of laminar flow profiles. The flight manual specifies that water on the wings and control surfaces can increase the stall speed by up to 3 knots.
Meteorological data confirmed that a moderate rain shower arrived at the aerodrome shortly before the accident, leading to a rapid degradation in visibility. The instructor reported difficulty maintaining external visual references during the final approach. The investigation also looked into the instructor's decision to continue the exercise despite the deteriorating weather conditions.
Findings
- The primary cause of the accident was the destabilization of the aircraft's flight path following flap extension, driven by reduced engine power and the aerodynamic degradation caused by heavy rain on the wings and control surfaces.
- The instructor's decision to proceed with the training maneuver despite rapidly worsening weather conditions contributed to the landing occurring short of the runway.
- Reduced visibility due to rain and canopy fogging prevented the instructor from detecting the loss of flight path stability.
- A lack of awareness regarding the specific performance impacts of water on modern laminar flow airfoils may have played a role.