Which items are not powered by the master switch's bus circuit?

Which items are not powered by the master switch's bus circuit?

• A. Ignition Switch, Clock and Flight Time Recorder
• B. Avionics Bus
• C. Elevator Trim System
• D. Navigation Lights

Answer: (A)

The main idea here is how power is distributed in an aircraft electrical system. The master switch energizes the main bus that supplies most equipment, so items on that bus depend on the master being ON. The ignition system is wired differently: magnetos generate sparks independently of the battery and main bus, and the ignition switch simply controls those magnetos. Because of that independent path, the ignition switch isn’t powered by the master switch’s bus circuit. The clock and flight time recorder also have their own or standby power paths, often designed to keep timekeeping even when the main bus is deenergized. Therefore, these items aren’t powered by the master switch’s bus circuit. In contrast, avionics, the elevator trim system, and navigation lights rely on the main distribution through the master switch.

The main idea here is how power is distributed in an aircraft electrical system. The master switch energizes the main bus that supplies most equipment, so items on that bus depend on the master being ON. The ignition system is wired differently: magnetos generate sparks independently of the battery and main bus, and the ignition switch simply controls those magnetos. Because of that independent path, the ignition switch isn’t powered by the master switch’s bus circuit. The clock and flight time recorder also have their own or standby power paths, often designed to keep timekeeping even when the main bus is deenergized. Therefore, these items aren’t powered by the master switch’s bus circuit. In contrast, avionics, the elevator trim system, and navigation lights rely on the main distribution through the master switch.