Electrical and Avionics Systems
Core concepts
Candidates must understand DC and AC power generation and distribution: batteries, starters, generators, alternators, inverters, transformers, rectifiers, bus bars, and circuit protection. Know the difference between a generator and an alternator (alternator produces AC rectified to DC; generator produces DC directly with a commutator). Understand bonding and grounding, shielded cables, and the role of static dischargers. For avionics, know pitot-static and gyroscopic instruments, air data computers, and the difference between VFR and IFR required equipment. Understand the magneto system: independent ignition, impulse coupling, and why the engine keeps running on one magneto. Know wire identification, routing separation from fuel lines, and the purpose of fuses versus circuit breakers.
Traps in questions
Questions often test whether a circuit breaker may be reset in flight: only once, and only if the crew has approved procedures and no smoke or burning odor is present. Another trap is confusing a bus tie with a bus bar, or assuming a generator and alternator are interchangeable terms. Watch for questions about bonding: bonding provides a low-resistance path for static and fault current, not a return path for normal load current (that is grounding). Also remember that a magneto is independent of the aircraft electrical system, so a total electrical failure does not stop ignition.
Worked example / rule of thumb
Rule of thumb: Ohm's law, V = I × R. A 28-volt circuit drawing 7 amps has 4 ohms resistance. If a 14-gauge wire has a rated current of 15 amps, a 7-amp load is acceptable with margin. For voltage drop, keep total drop below about 2 percent of system voltage (about 0.56 V on a 28-V system) for critical avionics.