ATPL question bank · Subject 021

Free Electrical Systems ATPL questions

AC and DC generation, distribution and protection — power for the whole aircraft.

What does Electrical Systems cover?

The electrical system generates, distributes and protects the power that runs avionics, lighting and many services. The exam tests generation (AC and DC), batteries, busbars and distribution, and the protective devices that isolate faults.

What this subject covers

  • DC and AC generation; the constant-speed drive
  • Batteries and their characteristics
  • Busbar systems and load shedding
  • Circuit protection: fuses, circuit breakers

Study tip

Follow the path of the power and what happens when a generator fails — busbar and load-shedding logic is a favourite exam target.

Frequently asked questions

Why do large aircraft use AC power?

AC can be generated at constant frequency and transformed easily, and it suits high-power loads; DC is derived from it for batteries and specific systems.

What is load shedding?

Automatically disconnecting non-essential electrical loads when generating capacity is reduced, to protect essential services.

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