Which power source is typically used to start engines and power most avionics?

Which power source is typically used to start engines and power most avionics?

• A. 28V DC
• B. 115V AC
• C. 400 Hz AC
• D. 28V AC

Answer: (A)

Engine starting and the majority of avionics rely on a single, high-current, regulated DC power source. In modern aircraft that role is the 28-volt direct-current system. The engine starters are DC motors fed from the 28V DC bus, supplied by the battery or an auxiliary power unit and engine-driven generators, which makes starting quick and reliable. Avionics are designed to run from this same 28V DC supply, with regulators keeping the voltage stable for sensitive electronics. The other voltage forms are used for specific systems or loads rather than starting and the bulk of avionics. 115V AC and 400 Hz AC appear in certain aircraft subsystems or accessories, often via inverters or transformers, but they aren’t the power source for starting or the primary avionics power. 28V AC isn’t a standard aviation power supply for these purposes.

Engine starting and the majority of avionics rely on a single, high-current, regulated DC power source. In modern aircraft that role is the 28-volt direct-current system. The engine starters are DC motors fed from the 28V DC bus, supplied by the battery or an auxiliary power unit and engine-driven generators, which makes starting quick and reliable. Avionics are designed to run from this same 28V DC supply, with regulators keeping the voltage stable for sensitive electronics.

The other voltage forms are used for specific systems or loads rather than starting and the bulk of avionics. 115V AC and 400 Hz AC appear in certain aircraft subsystems or accessories, often via inverters or transformers, but they aren’t the power source for starting or the primary avionics power. 28V AC isn’t a standard aviation power supply for these purposes.