Radio Navigation and Instrumentation
Radio Navigation and Instrumentation
This domain covers VOR, ADF, GPS, ILS, transponders and basic flight instruments: pitot-static, gyroscopic and magnetic compass. Questions test interpretation of indications, not button-pushing.
Core rules
- VOR: radials are magnetic bearings from the station. With the OBS set and the CDI centred, a TO indication means you are on the reciprocal radial flying toward the station; a FROM indication means you are outbound on the selected radial.
- ADF: the needle points to the station relative to the aircraft nose; the relative bearing plus heading gives the magnetic bearing to the station.
- ILS: localiser gives runway centreline; glideslope gives vertical path; marker beacons or DME give distance.
- Transponder: code 7700 for emergency, 7600 for radio failure, 7500 for unlawful interference. Mode C reports altitude.
- Instruments: the attitude indicator and heading indicator are gyroscopic; the altimeter, airspeed indicator and VSI are pitot-static. The magnetic compass turns errors in northerly and southerly turns.
Worked example
You select 090° on the VOR OBS and the CDI centres with a TO flag. The selected course is toward the station, so you are on the 270° radial, west of the station, tracking 090° inbound. If you turned outbound with the same setting, the TO/FROM flag would reverse and reverse sensing could mislead you.
Traps that cost marks
Reading a VOR radial as the course you are flying, forgetting the ADF relative-bearing conversion, and relying on the magnetic compass in a turn are common. A centred CDI does not by itself prove you are on the selected radial unless the TO/FROM flag is read correctly.