The 1993 Llyn Padarn helicopter crash occurred on 12 August 1993, when an RAF Westland Wessex helicopter, serial number XR524, with 3 aircrew and 4 Air Training Corps cadet passengers on board suffered a catastrophic tail rotor failure and plunged into Llyn Padarn, a lake in North Wales.

[2] The aircraft departed RAF Valley[3] on 12 August 1993, for a routine search and rescue training mission over North Wales.

[Note 1] Without it to counteract the torque produced by the main rotor, the helicopter became uncontrollable[1] and started spinning before impacting the water.

The shaft that drives the tail rotor is broken and then remade by means of a disconnect coupling using two flanges.

It is hypothesized that the disconnection of the autopilot just prior the accident increased the stress on the tail section, triggering the failure.

As of 2000, at least one of the four recommendations made by the military board of inquiry as a result of the crash (simulator training for a tail rotor failure) had been implemented.