Instrument Navigation Systems and Radio Aids
What this domain tests
Radio navigation and area navigation: how VOR, DME, NDB, ILS and GNSS behave in the air, and whether you can compute a heading, an intercept or a DME arc without trial and error.
The core aids
A VOR gives a radial (magnetic, from the station); a DME gives slant range in nautical miles, so it over-reads directly overhead by roughly your altitude in miles. NDB/ADF senses the bearing to the station and is vulnerable to thunderstorm static, night effect and coastal refraction, all relevant in a tropical archipelago. ILS gives lateral guidance from the localiser and vertical guidance from the glideslope, with marker beacons or DME as fixes. GNSS/RNAV provides point-to-point navigation with RNP containment; RAIM prediction and receiver fault detection are the integrity checks, since the Philippines has no SBAS coverage.
Tracking and intercepting
Outbound on a radial, track equals the radial. Inbound, track equals the radial ±180°. Correct for wind with the wind correction angle (WCA): WCA ≈ arcsin(crosswind ÷ TAS). Intercept angles of 30–45° are standard; lead the turn onto the radial by roughly half your intercept angle.
Worked example
Tracking R-090 outbound from a VOR at TAS 120 kt, wind 360°/20 kt. The wind is at 90° to track, so the full 20 kt is crosswind from the left. WCA = arcsin(20 ÷ 120) ≈ 9.6°, round to 10° right, giving heading 100°. The headwind component is 20 × cos 90° = 0, so groundspeed stays about 120 kt. On a 10 DME arc at that speed, use a lead of about 5–6° of radial to roll out on the inbound course.
Traps
Setting the OBS to the outbound radial and reading the wrong sensing; forgetting that DME is slant range; using a VOR beyond line-of-sight or on the wrong side of a mountain; trusting ADF in a CB; assuming GPS integrity without a RAIM check.