At what percentage should starter dropout occur?

Starter dropout is an important aspect of the engine start sequence, specifically related to the operational limits of the engine's N2 speed which signifies the rotational speed of the high-pressure compressor and turbine. The correct percentage for starter dropout typically occurs at 45% N2.

During the engine start process, starters are utilized to bring the engine up to a certain speed before they are disengaged. This dropout point is critical for ensuring that the engine has sufficient power and momentum to continue running on its own after the starter is removed. If the starter disengages at too low a percentage of N2, the engine may not have enough thrust to sustain combustion, leading to a potential start failure.

Starting the engine effectively at this dropout point helps to ensure a reliable transition from starter assistance to the engine's own thrust generation capabilities, thereby maintaining operational integrity and efficiency.