When the landing gears are up and the throttles are retarded, the warning horn will not sound if an open occurs in wire _______.

When the landing gears are up and the throttles are retarded, the warning horn will not sound if an open occurs in wire _______.

• A. No. 2
• B. No. 3
• C. No. 5
• D. No. 4

Answer: (D)

The key idea is that an electric horn only sounds when there is a complete current path. In the landing gear warning system, the horn is energized only if the gear-up/idle-throttle condition would demand an alert, which requires all parts of the circuit to be closed. If there is an open in the wire that provides the return path for the horn current (the conductor that completes the circuit back to the power source/ground), the current cannot flow. No current means no energizing of the horn, so it will not sound even under the conditions that would normally trigger it. This is why an open in that particular wire stops the horn from sounding.

The key idea is that an electric horn only sounds when there is a complete current path. In the landing gear warning system, the horn is energized only if the gear-up/idle-throttle condition would demand an alert, which requires all parts of the circuit to be closed. If there is an open in the wire that provides the return path for the horn current (the conductor that completes the circuit back to the power source/ground), the current cannot flow. No current means no energizing of the horn, so it will not sound even under the conditions that would normally trigger it. This is why an open in that particular wire stops the horn from sounding.