When the gear was selected down it did not fully extend and the gear circuit breaker tripped. Initially the circuit breaker could not be reset nor could the gear be lowered using the emergency system. The circuit breaker was subsequently reset and a gear down indication obtained. Shortly after touchdown the aircraft yawed until it was travelling backwards. The tailskid struck the runway and the aircraft came to rest after turning through a further 90 degrees. The right main wheel was found to have turned through 90 degrees because the scissor linkage arms had become disconnected. A castellated nut and its retaining split pin was found to be missing from the bolt which joins the scissor linkage arms. The reason for the loss of these items could not be positively established.
