How does the electrical system support engine start?

How does the electrical system support engine start?

• A. External power is always required to start engines.
• B. The battery provides power to start the engine; once running, the engine-driven generators supply power to the buses and TRUs convert AC to DC for DC loads.
• C. Only the APU provides start power.
• D. The standby inverter supplies start power.

Answer: (B)

Starting the engines relies on the battery as the prime power source. The battery powers the engine starter to rotate the engine until ignition occurs. Once the engine is running, the engine-driven generators take over and supply the electrical system, feeding the buses with AC power. Those generators also provide the power that keeps both the AC and the DC systems operating, while the Transformer Rectifier Units convert the AC to DC to power the DC loads. This sequence allows a start without external power and then maintains normal operation through the engine-driven generators.

Starting the engines relies on the battery as the prime power source. The battery powers the engine starter to rotate the engine until ignition occurs. Once the engine is running, the engine-driven generators take over and supply the electrical system, feeding the buses with AC power. Those generators also provide the power that keeps both the AC and the DC systems operating, while the Transformer Rectifier Units convert the AC to DC to power the DC loads. This sequence allows a start without external power and then maintains normal operation through the engine-driven generators.