What happened
On 5 March 2000, a Piper PA-25-235 Pawnee D, registration G-BEII, was engaged in private aerotow operations near Eggborough, South of Selby, North Yorkshire. The aircraft had recently returned to service following its annual inspection on 3 March. During the course of approximately 10 to 20 aerotows on Sunday, the pilot of a trailing glider observed the tailwheel assembly detach from the tug aircraft and fall toward the ground while at an altitude of 3,500 feet.
The pilot of G-BEII remained unaware of the detachment during the flight. It was only after landing on the runway that a scraping sound was heard as the aircraft decelerated. Upon inspection, the pilot initially suspected a flat tyre, but discovered that the tyre, wheel, and fork assembly were entirely missing from the aircraft. The detached components were not recovered.
The investigation
The investigation focused on the mechanical attachment of the tailwheel assembly. The design of the Piper PA-235 Pawnee D utilizes a tailwheel held within a fork assembly that allows for castoring during taxiing. This fork is secured to a stationary fitting by a vertical spindle, which is held in place by a castellated nut and a split pin. Under normal operating conditions, the presence of an inflated tyre would obscure the nut and pin from view.
Investigators reviewed the aircraft's recent maintenance history, noting that the annual inspection completed two days prior to the incident had required only the servicing of the wheel itself, a task that does not necessitate the removal of the fork assembly. No specific defects were identified during that inspection.
Findings
- The tailwheel, wheel, and fork assembly all detached from the aircraft during flight.
- The pilot of the tug aircraft was not aware of the loss of the assembly until after landing.
- The split pin or castellated nut may have been absent due to an error during a previous maintenance event or subsequent manual removal.