The air starter, coded P51309-16, is a critical auxiliary system in the MAN L21/31 engine, enabling smooth and reliable engine startup. By using compressed air to drive a small turbine or motor, the air starter turns the engine crankshaft until the first combustion cycle begins. This robust system is particularly advantageous for large diesel engines, where electric starters are impractical. Dependable air starters are key to operational readiness and safety in marine and power generation applications.