In the landing gear system, placing the control valve switch in the neutral position serves to:

• A. Permit the test circuit to operate.
• B. Remove the ground from the green light.
• C. Allow hydraulic pressure to return to normal.
• D. Prevent the warning horn from sounding when the throttles are closed.

Answer: (D)

The key idea is how the landing gear warning system is wired to alert you when the gear isn’t down and locked while the engine is at idle. The control valve switch, when placed in the neutral position, interrupts the electrical path that would energize the warning horn under those conditions. In other words, with the valve in neutral, the horn cannot complete its circuit, so it won’t sound when the throttles are closed. This keeps nuisance warnings from occurring in situations where the system isn’t signaling a real gear problem.

The other options aren’t what this switch in neutral is doing. It isn’t primarily about enabling a test circuit, it doesn’t directly affect the grounding for the green gear-down light, and it isn’t a mechanism for returning hydraulic pressure to normal. The essential effect of the neutral position is to disable the warning horn circuit when throttles are closed.