What device on small turbine engines serves both as a starting mechanism and as an electrical power source?

• A. An auxiliary power unit
• B. A starter-generator
• C. A synchronous generator
• D. A motor/generator set

Answer: (B)

A starter-generator is the device that both starts a small turbine engine and provides electrical power once the engine is running. It’s a single unit connected to the engine’s accessory gear train. During start, it functions as a motor, drawing electrical power to turn the engine until it reaches self-sustaining speed. Once ignition occurs and the engine runs, the same unit switches to generating mode, converting mechanical energy from the spinning engine into electrical power for the aircraft systems and to recharge the battery. This integrated approach saves weight and space compared with having separate starting motors and generators. The other options describe separate systems or a generator-only device and do not provide both functions in one unit.