Which piece of equipment is included in the hot battery bus?

The hot battery bus is a critical component of the electrical system in the T-6A, as it provides power to certain essential systems even when the aircraft is not actively running or when the engines are shut down. Among the equipment connected to the hot battery bus are systems that require continuous power for safety or operational readiness.

Emergency flaps are included in the hot battery bus because they are vital for safe landing in case of an emergency situation. These flaps must be capable of functioning independently of the aircraft's main electrical system and should be available for immediate use regardless of the aircraft's operational state. This ensures that flight crews have the necessary capability to manage their descent and landing safely, even if other systems might be offline.

In contrast, the other options, such as fuel gauges, the fire warning system, and radios, are typically powered by different electrical buses that do not retain power when the aircraft is switched off. This distinction makes emergency flaps essential within the hot battery bus system, as they play a critical role in the safety and emergency operations of the aircraft.