What happened
On August 26, 2000, at approximately 18:30 local time, a Robin DR 400/200R, registration F-OIPA, was performing a glider tow operation at the Pavullo nel Frignano airport. The aircraft was towing an ASK 21 glider, registration D-9490.
During the initial climb and subsequent left turn, the towing aircraft experienced a sudden loss of airspeed and altitude. The pilot of the F-OIPA successfully released the tow cable, but the aircraft entered a steep dive and struck the roof of a building on the outskirts of the town. The impact caused a violent fire, fueled by leaking fuel, which completely destroyed the wooden and fabric structure of the aircraft. The pilot of the towing aircraft sustained fatal injuries. The glider, which remained attached to the tow cable, continued its turn and landed safely following standard procedures.
The investigation
The ANSV investigation focused on the sequence of events following the takeoff and the state of the aircraft's engine controls. Investigators examined the wreckage and found that the magneto switch was in the OFF position. Analysis of the propeller showed that it was nearly stationary at the moment of impact, indicating the engine was not producing power.
While the investigation considered the possibility of pilot error by the glider pilot, no evidence was found to support that the glider's flight path contributed to the accident. The investigation also noted that no pre-flight briefing or radio communication had taken place between the two pilots regarding emergency procedures.
Findings
- The primary cause of the accident was the accidental shutdown of the engine by the pilot of the F-OIPA. While attempting to follow the flight manual's procedure for addressing engine vibrations, the pilot mistakenly moved the magneto switch to the OFF position instead of switching between the left and right magnetos.
- This error caused an immediate loss of engine power and a rapid reduction in airspeed, leading to an aerodynamic stall during the climbing turn.
- The low altitude at the time of the stall left the pilot with insufficient margin to recover the aircraft.
- The lack of a pre-flight briefing between the towing and glider pilots regarding emergency protocols contributed to the lack of coordination during the event.