What happened
On March 20, 2011, an Aerospool Dynamic WT9, registration PH-3Z2, was performing a local flight from Teuge Airport (EHTE). Shortly after beginning its takeoff roll on runway 27, the pilot noticed that the cover for the oil filler cap was open. In response to this observation, the pilot decided to abort the takeoff by pulling the throttle back.
During the reduction of power, the aircraft began to veer to the right. The pilot attempted to correct this with left rudder input. However, the pilot unintentionally pushed the throttle forward again. This sudden application of power caused the aircraft to lift briefly off the runway and veer sharply to the left. The aircraft subsequently exited the runway into the grass. The impact caused the nosewheel to break off and resulted in significant damage to the propeller blades and engine cowling. There were no injuries to the two occupants, who were able to exit the aircraft unaided.
The investigation
The investigation focused on the aerodynamic forces acting on the aircraft during the power transitions. In single-engine aircraft with a right-turning propeller, the slipstream creates a leftward force that must be countered with right rudder. This effect is particularly pronounced in modern micro-light aircraft when power is high relative to the aircraft's mass.
Investigators determined that when the pilot initially reduced power to abort the takeoff, the aircraft veered right because the pilot maintained the previous rightward control input while the leftward torque from the propeller decreased. When the pilot subsequently applied power again without sufficient right rudder correction, the aircraft veered left and became airborne briefly before the nose was forced down.
Findings
- The pilot's reaction to the open oil cap cover caused a startle response.
- The pilot's insufficient experience and knowledge prevented them from maintaining control of the aircraft during these unexpected power changes.
- The sudden increase in power without adequate rudder compensation led to the loss of directional control and the runway excursion.