What happened
On the afternoon of 13 June 2021, a Citabria 7ECA, registration EI-ANT, was performing circuits at Trim Airfield in Co. Meath. The aircraft was being operated as part of a private flight involving two occupants: a handling pilot in the front seat and a licensed pilot in the rear seat acting as an observer.
After completing two circuits, the aircraft performed a three-point landing on Runway 28. The aircraft decelerated to approximately 30 mph, at which point the pilot applied power to begin a ground roll for a third circuit. As the aircraft accelerated to between 35 and 40 mph, it suddenly and violently swung to the left. The aircraft departed the side of the runway, crossed the grass shoulder, and crashed through a barbed wire boundary fence before coming to a stop in an adjacent field. The impact caused significant damage, including a fractured right wing and a separated left undercarriage leg, resulting in the aircraft being destroyed. Both occupants exited the aircraft without injury, and no fire occurred.
The investigation
The AAIU examined the wreckage and the runway at the accident site. Investigators noted that the aircraft had touched down to the left of the runway centerline. The survey of the runway showed that the deviation from the centerline began approximately 140 meters from the threshold, leading the aircraft across the 2-meter wide shoulder and through the fence.
Technical inspections of the aircraft revealed that the wheel brakes were functioning normally with no evidence of binding. The investigation also reviewed the aerodynamic forces acting on the aircraft, specifically those related to the propeller's clockwise rotation, such as P-factor, torque effect, and prop-wash, which can induce leftward yawing moments in single-engine aircraft.
Findings
- The aircraft featured a tailwheel (tail-dragger) configuration, which inherently possesses directional instability during ground maneuvers.
- The aircraft's tailwheel was non-steerable, meaning it could castor freely.
- The aircraft touched down to the left of the runway centerline, which reduced the available margin for error and recovery.
- Aerodynamic forces, including propeller torque, P-factor, and prop-wash, likely exacerbated the leftward yawing tendency during the application of power at low airspeed.