Slingsby T67M260 Firefly, G-BYOB
As the crew carried out functional checks of the flight controls while taxiing for takeoff, the left wheelbrake master cylinder became detached from the rudder/brake pedal mechanism. The failure was consistent with the effects of previous overload and consequent weakening of the mechanism as a result of inadvertent exceedance of the maximum allowable nosewheel steering angle during ground towing. In this situation, as the primary steering stops were within the pedal mechanism rather than on the nosewheel leg, the mechanism could be severely overloaded. Damage could both weaken the mechanism and reduce the clearances between its moving parts and other components, potentially preventing operation of the rudder and/or wheelbrake controls, and could remain undetected for a considerable time. The aircraft manufacturer had taken a number of measures aimed at reducing the likelihood of the pedal mechanism being damaged during towing. A relatively minor aircraft modification could probably eliminate the possibility of such damage. Three safety recommendations are made.
Published 10 December 2014