At what fuel pressure do the igniters and starter de-energize?

The correct answer is that the igniters and starter de-energize above 10 PSI. Typically, aircraft ignition systems are designed to operate under certain fuel pressure thresholds to ensure proper engine operation. When the fuel pressure reaches a level above 10 PSI, it indicates that there is adequate fuel flow and pressure to support combustion and the normal functioning of the engine.

At this point, the system can safely de-energize the igniters and starter because the likelihood of a flameout or insufficient fuel supply is minimal. Fuel systems are controlled to ensure that the igniters and starters operate only when necessary, thus promoting efficiency and reducing unnecessary wear and tear on the components.

This operational threshold is important for maintaining the stability and safety of the engine during its ignition and startup phases. Other figures such as 30 PSI, 40 PSI, and 10 PSI individually do not represent the deactivation point; thus they do not apply in this context.