Incident Overview
On 5 March 2000 at 1430 hours UTC, a Piper PA-25-235 Pawnee D, registration G-BEII, experienced the loss of its tailwheel assembly while in flight near Eggborough, South of Selby, North Yorkshire. The aircraft was engaged in a private flight towing gliders. The single pilot on board was uninjured.
Aircraft Details
The aircraft was a Piper PA-25-235 Pawnee D, manufactured in 1976 and powered by one Lycoming O-540-B2C5 piston engine. It had recently returned from its Annual Inspection on 3 March 2000.
Sequence of Events
On the day following the inspection, the aircraft completed 15 to 20 aerotows. On 5 March, after approximately 10 tows, the pilot of the glider being towed observed the tailwheel assembly detach from the tug aircraft and fall toward the ground. This occurred at an altitude of 3,500 feet. The pilot of the tug aircraft was unaware of the loss until landing on the runway, when a scraping sound was heard after touchdown. As the aircraft slowed, it appeared that the noise originated from the rear. The pilot suspected a flat tailwheel tyre and taxied carefully. Upon inspection, the tyre, wheel, and fork assembly were all missing. The missing parts have not been found.
Examination and Possible Explanations
In the PA25 Pawnee, the tailwheel design is similar to that in a PA18 Super Cub. The tailwheel is held in a castoring fork assembly, secured to its stationary fitting by a vertical spindle with a castellated nut and split pin at its lower end. With an inflated tyre in place, the nut and split pin are normally not visible. The Annual Inspection had not indicated any required work on the tailwheel area other than servicing the wheel itself, which would be performed without removing the fork. There is no ready explanation for the occurrence, but the possibilities exist that, during a previous maintenance input, the split pin was inadvertently omitted during re-assembly or that it was deliberately removed at a later time.