Navigation (General Navigation, Radio Navigation, Instrumentation)
What the exam tests
General navigation, radio navigation and instrumentation: Earth geometry, magnetism, VOR/DME, ILS, GNSS and basic instrument interpretation.
Core rules
- A great circle is the shortest path; a rhumb line cuts meridians at a constant angle.
- Variation is the angle between true and magnetic north; deviation is aircraft-specific and comes from the compass.
- VOR gives the radial from the station; the CDI centres when the OBS is set to the bearing. DME gives slant range, so it over-reads ground distance at close range.
- ILS localizer is 108–112 MHz, glideslope 329–335 MHz; a 3° path is about 300 ft per nautical mile.
- GNSS RNAV needs adequate RAIM or SBAS; an INS/IRS must align before departure.
- Transponder Mode C gives pressure altitude; Mode S adds aircraft identification.
Worked example
Aircraft on radial 090 at 40 DME from a VOR is 40 nm east of the station at the same altitude. If the station is at 1,000 ft and the aircraft at 5,000 ft, slant range is greater than 40 nm, so the true ground distance is slightly less than 40 nm.
Traps
Applying variation the wrong way (east is least, west is best for converting true to magnetic); confusing radial with bearing to the station; and using DME as exact ground distance.