Radio navigation aids and systems
Radio navigation aids and systems
This domain tests whether you can turn a VOR, DME, NDB or ILS indication into a position and a tracking instruction.
VOR. The OBS selects the radial - a magnetic bearing from the station. With TO indicated you are tracking inbound on the reciprocal of the selected radial; with FROM you are outbound. The CDI centres when you are on the selected radial; full-scale deflection is typically ±10°. In the cone of confusion above the station the TO/FROM flag may flicker - do not chase it.
DME. Slant range, not ground distance. Error is small beyond about three times your height above the station: at 6,000 ft and 1 NM ground range, slant range ≈ √(1² + 1²) ≈ 1.4 NM.
NDB/ADF. Magnetic bearing to the station = aircraft magnetic heading + relative bearing. The ADF is affected by thunderstorm static, coastal refraction and night effect.
ILS. Localizer gives lateral guidance, glideslope normally 3.0°; fly to the decision altitude/height. A 3° path rises about 300 ft per NM.
Surveillance. NZ requires ADS-B in controlled airspace; Mode A/C transponders with 4096 codes remain standard, and 7500/7600/7700 are the emergency codes.
Worked example. Heading 090°M, ADF relative bearing 030°. Bearing to station = 090 + 030 = 120°M. To fly directly to the station, turn right to 120°M. If the station is 20 NM away and you are 4 NM right of the 120°M bearing, track error = (4 × 60)/20 = 12°; turn left 12° to parallel, plus a closing angle for the distance to go.
Traps. Adding relative bearing to track instead of heading; reading DME as ground distance; selecting a radial and flying the wrong end; and forgetting that VOR radials are magnetic while chart grid is true.