A clutch in a pneumatic starter must perform three basic functions:
Transmit starter turbine torque to the engine shaft when the starter turbine torque is accelerating the engine shaft.
Prevent the output shaft from driving the starter turbine when the engine shaft speed exceeds the starter turbine speed.
Allow re-engagement when the engine shaft is already rotating (running engagement).
Previous clutch designs were capable of achieving the first two requirements, but were limited in their ability to successfully achieve running engagements. In many instances, “crash re-engagements” occurred, often damaging the starter and typically causing an operational disruption. A solution is the synchronous engagement clutch which permits running engagements at any starter operating speed. The synchronous engagement clutch represents a paradigm shift in clutch design for pneumatic starters which increases the operational flexibility of the pneumatic starter.