Leon Solent
Striker
A visual inspection during service should have picked up an incorrectly fitted split pin. In normal use a split pin carries no load so is not under stress. The assembly to which it is fitted should already be secure and the pin is there to prevent slackening should that security be lost (slackening). From the AAIB report the foot pedals became detached from the rotor actuator linkage and feedback signal was lost. Once lost it allowed the rotor blades to fail to full pitch with no control over them, as was a common occurrence in controllable pitch propellers at sea until suitable modifications were made. At full pitch the helicopter began to yaw (rotate about a vertical axis) with no control. It was effectively 'lost' from then on. Split pins have been fazed out of most industries where component security is critical. They are cheap and cheerful, shouldn't be re-used, disposable, and they do work but a thorough visual inspection will turn up an incorrectly fitted or damaged pin.
I would expect recommendations from the report to include a modification to the failure mode from that of 'fail to full pitch' to either 'fail to zero pitch', where no sideway thrust is developed, or 'fail to a pre-calculated pitch' sufficient to prevent yaw and maintain the helicopter's stability. These failure mode modifications are relatively easy to achieve and were made to ships' CPP systems twenty years ago following several incidents of collisions caused by propellers failing full ahead or full astern, with no control, during manœuvring.
A friend of mine's brother was CEO of a leading helicopter operator in that field. He resigned because of the overhaul of engine practices adopted by the company. He took up the job of head of flights for the Sultan of Oman's fleet. The company he left have been in the news occasionally.
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