Rotorcraft Electrical, Avionics and Instrument Systems
Electrical, avionics and instrument questions test the 28 V DC distribution, engine and rotor indication, pitot-static systems, and the checks that keep avionics legal and reliable.
Electrical system
Most helicopters use 28 V DC: battery, starter-generator or alternator with rectifier, master relay, split bus and avionics bus. Circuit breakers protect wiring; a popped breaker should not be reset in flight unless the manual authorises it and the load is essential. Alternator capacity must cover the load analysis with failed-generator contingency. Piston helicopters use magnetos with an ignition switch that grounds the primary circuit; a broken ground wire is a live-mag hazard.
Instruments and avionics
Rotor and engine tachometers (NR, N1, N2), torque, TGT/TOT, manifold pressure and fuel flow are the core indications. Torque may be sensed hydraulically or by strain gauge. Pitot-static systems need clear static ports; blocked statics cause airspeed, altitude and VSI errors. Transponder, altimeter and static system checks, compass swings and ELT inspections follow the maintenance schedule. ADS-B and GPS installations require configuration and data checks.
Worked example
After adding avionics, the ammeter shows a steady discharge in cruise. Reasoning: complete a load analysis, confirm alternator output and belt condition, check the avionics bus and breaker sizing; do not simply fit a larger battery.
Traps
- Resetting a tripped breaker without finding the fault.
- Confusing NR with N2 on a dual tachometer.
- Signing a transponder or static check without the required test equipment.