FAA Powerplant Written Practice Test

In a thermal switch type fire detection system, how are heat-sensitive switches arranged?

1. Series; parallel with the flight deck indicator lights

2. Parallel; series with the flight deck indicator lights

3. Independently; with no connection to indicator lights

4. In a single row; with a direct connection to the power source

The correct answer is: Parallel; series with the flight deck indicator lights

In a thermal switch type fire detection system, the heat-sensitive switches are arranged in a parallel configuration with the flight deck indicator lights. This design allows for multiple switches to monitor the same area for heat, enhancing redundancy and reliability in detecting potential fire conditions. When the thermal switches detect a specific temperature indicative of fire, they close the circuit, which powers the indicator lights in the flight deck. This parallel arrangement ensures that if one switch fails or does not detect the heat, other switches can still function and activate the alarm system. The use of parallel wiring is crucial because it allows for consistent monitoring of temperature across different zones without relying on a single point of detection. Thus, if any one switch activates due to excessive heat, it will signal the indicator lights, providing critical information to the flight crew about a potential fire hazard.