The starter motor will automatically drop out at ______.

• A. 40 percent N2
• B. 43 percent N1
• C. 14 percent N1
• D. 62 percent NR

Answer: (B)

The starter motor in turbine engines is designed to disengage automatically once a specific parameter is reached, ensuring efficient engine start-up and protection of the starter system. The correct choice, 43 percent N1, represents the point at which the engine has reached sufficient speed and internal conditions for the starter to no longer be necessary.

N1 refers to the rotational speed of the low-pressure compressor section and is critical for maintaining optimal engine performance. At 43 percent N1, the engine is typically established enough in its operation to sustain combustion without the aid of the starter, allowing it to disengage and preventing unnecessary wear or overheating of the starter motor.

Other options refer to different engine parameters that either do not represent the correct point for starter disengagement or relate to components that are not directly associated with the automatic drop-out of the starter motor. Therefore, understanding the functioning and operational parameters of the engine is vital to recognizing why 43 percent N1 is the appropriate threshold for the starter motor's automatic drop-out.