RPAS Systems
The exam tests system knowledge at the level needed to predict failure: what each subsystem does, how it degrades, and which configuration choices create risk.
Core architecture
Flight controller; IMU with accelerometers and gyros; barometer; magnetometer; GNSS receiver; ESCs and motors; RC control link; telemetry; video downlink; gimbal and payload; power distribution; geofence and failsafe logic.
Degradation modes
- GNSS loss: the aircraft drops to attitude mode, loses position hold and drifts with wind; hovering becomes a pilot skill.
- Compass error: yaw drift, circular "toilet-bowl" motion, and in severe cases a fly-away as the controller fights a false heading.
- Barometer drift: altitude hold wanders, especially in gusty or hot conditions, so AGL margin must be generous.
- IMU drift or thermal error: false horizon, poor levelling.
- Link loss: failsafe action fires, which is only as safe as the pre-set RTH height and route.
Configuration discipline
Calibrate away from ferrous metal and strong current; allow IMU warm-up; track firmware versions across the fleet; set geofence radius and height; define low-battery actions with a reserve; verify payload mass against the flight manual.
Worked example
After takeoff the aircraft holds position but slowly rotates and drifts in a circle. The launch pad was a steel-reinforced loading dock. Reasoning: a bad compass calibration corrupts the heading solution, so position hold commands push the aircraft the wrong way. Correct action is to land promptly in attitude mode, relocate, recalibrate and re-fly.
Traps
Treating a GNSS lock as proof of accurate altitude (barometric and GNSS altitude diverge); trusting a geofence to exclude a NOTAM zone; skipping calibration because it worked yesterday.