Navigation, Radio Aids and Air Traffic Services
What the exam tests
This domain covers navigation principles and the radio/ATS environment: true and magnetic direction, variation and deviation, great-circle and rhumb-line tracks, VOR/DME, NDB, GNSS, RNAV/PBN, SSR, ADS-B, ATC clearances, position reporting, and RVSM.
Core concepts
- True course is referenced to true north; magnetic heading is referenced to magnetic north and affected by aircraft deviation.
- Variation is the angle between true and magnetic north; deviation is the aircraft-installation error.
- VOR gives bearing; DME gives slant range; NDB gives relative bearing; GNSS provides position and RNAV guidance.
- PBN specifications state the navigation accuracy required, such as RNAV 5 or RNP 1. The aircraft and crew must be approved for the specification.
- ATC clearances must be read back, especially route, altitude, heading, speed, and SSR code.
Worked example
True course 090. Variation is 5 W, so magnetic course = 090 + 5 = 095. Deviation is 2 E, so compass heading = 095 - 2 = 093. The dispatcher checks that the planned airway and aircraft navigation specification support the route, then confirms the ATS flight plan and clearance readback. A sign error here can put the aircraft off track.
Traps
Adding easterly variation instead of subtracting; confusing course, heading, track, and bearing; assuming GNSS equals PBN approval; and failing to read back an altitude or SSR code. Also remember that an ATC clearance may differ from the filed route.