What type of circuit breaker may not be used in an aircraft?

The automatic resetting type of circuit breaker may not be used in an aircraft due to safety and reliability concerns. In aviation, it is critical to maintain control and awareness of electrical systems, especially during flight. An automatic resetting circuit breaker will react to a fault and reset itself without the pilot's knowledge, potentially allowing a malfunctioning system to re-energize. This could lead to further damage or create hazardous conditions onboard.

In contrast, manual resetting types are commonly used because they require the pilot to consciously reset the breaker after it trips, ensuring that any issues are assessed before re-energizing the circuit. Fuses provide another level of protection, as they are designed to blow and must be replaced after a fault, completely severing the electrical flow until the issue is resolved. Hydraulic types are specialized for systems where fluid under pressure is used to actuate components, but their application is typically limited to non-electrical systems.

Therefore, the design and operational requirements of aircraft systems necessitate that circuit breakers are easily monitored and controlled, reinforcing the reason why automatic resetting circuit breakers are not suitable for use in aviation.