Aircraft General Knowledge – Electrics
Electrics covers DC generation, batteries, bus distribution, circuit protection, bonding and indications. The CPL exam tests system logic: what happens when an alternator fails, which bus feeds which load, and how to interpret ammeter and voltmeter readings.
Generation and distribution
A 28 V DC alternator with rectifier and voltage regulator supplies the main bus; the battery provides standby and starting power. A split bus or essential bus keeps critical avionics alive. Two 12 V batteries in series give 24 V; in parallel they keep 12 V but double capacity. Circuit breakers protect wiring; bonding returns current and prevents static build-up.
Worked example
A 28 V alternator is rated 50 A. Maximum power = 28 × 50 = 1400 W. With a 35 A load, 15 A remains to charge the battery. If load rises to 55 A, the alternator is overloaded; the battery supplies the difference and will discharge. After an alternator failure, shed non-essential load and land as soon as practical.
Traps
Reading an ammeter as bus voltage; forgetting the battery contactor; assuming a circuit breaker may be reset without finding the fault; confusing AC and DC indications; ignoring load shedding after a generator failure.