What happened
On 19 February 2005, a Scheibe SF25C, registration G-FLKS, completed a 30-minute private flight in clear, sunny weather. Upon landing at the London Gliding Club in Dunstable, the aircraft encountered a northerly wind of approximately 20 knots. After coming to a halt, the pilot disengaged the tail wheel to allow it to castor freely.
While taxiing to the launch point, the pilot held the control stick in the full aft position and initiated a right-hand turn. After the aircraft had turned roughly 80 degrees, it lost momentum and stopped. The pilot then applied additional power while maintaining the stick in the back position. This action caused the tail to lift abruptly, resulting in the propeller striking the ground and shattering. The engine continued to run for several seconds before the pilot could shut it down.
The investigation
The investigation examined the aircraft's configuration and the environmental conditions at the time of the incident. Investigators looked into the state of the tail wheel lever, which was found in the locked position when the pilot exited the aircraft, though it was noted this could have been disturbed during egress. The study focused on the aerodynamic forces acting on a tail-wheel aircraft during ground maneuvers in high-wind conditions.
Findings
- The incident occurred during ground maneuvering in strong, 20-knot winds.
- In tail-wheel aircraft, applying power and rudder during a crosswind turn can create a nose-down pitching moment, especially if differential braking is used.
- The propeller struck the ground because the tail lifted rapidly during the application of power.
- Strong winds can deflect the propeller slipstream away from the tail surfaces, reducing the downward force typically provided when the stick is held back.
- A tailwind component may have further contributed to the instability of the aircraft during the maneuver.