Aviation Navigation
VOR, NDB, GPS/GNSS, magnetic variation, dead reckoning, and course interception — the complete navigation fundamentals reference for PPL through ATPL.
Navigation is the science of determining and maintaining the position and track of an aircraft over the ground. Modern aviation uses a combination of ground-based radio aids (VOR, NDB, ILS), satellite navigation (GPS/GNSS), and traditional dead reckoning techniques.
Navigation Systems Overview
Navigation Fundamentals
All aviation navigation is built on a small set of core concepts. Understanding these allows a pilot to use any navaid — or no navaid at all — with confidence.
True vs Magnetic North
Aeronautical charts measure course in True degrees (referenced to the geographic North Pole). Aircraft instruments, VOR radials, runway headings, and ATC clearances use Magnetic degrees (referenced to the Magnetic North Pole). The difference is magnetic variation. See Magnetic Variation for the TVMDC conversion chain and worked examples.
Bearing, Track, and Heading
| Term | Abbreviation | Definition |
|---|---|---|
| True Course | TC | Direction from A to B measured on a chart, referenced to True North |
| True Heading | TH | Direction the aircraft nose points, referenced to True North; TC ± Wind Correction Angle |
| Magnetic Heading | MH | TH corrected for magnetic variation; what the compass/DI shows |
| Compass Heading | CH | MH corrected for compass deviation; what the compass physically reads |
| Track | TR | Actual ground path of the aircraft — should equal TC when WCA is correct |
Distance and Speed
- Nautical mile (nm): 1 nm = 1,852 m = 6,076 ft. One minute of arc of latitude. Standard distance unit in aviation.
- IAS (Indicated Airspeed): what the airspeed indicator reads — subject to instrument error and position error.
- CAS (Calibrated Airspeed): IAS corrected for instrument and position errors.
- TAS (True Airspeed): CAS corrected for altitude and temperature — actual speed through the airmass.
- GS (Groundspeed): TAS modified by the wind — actual speed over the ground used for ETAs and fuel calculations.
Radio Navigation Aids
| Navaid | Frequency Band | Range | Accuracy | Type |
|---|---|---|---|---|
| NDB | 190–1750 kHz (LF/MF) | 50–200 nm | ±5° | Non-precision bearing only |
| VOR | 108.0–117.95 MHz (VHF) | 25–130 nm | ±2–3° | Non-precision bearing, radials |
| DME | 962–1213 MHz (UHF) | ~200 nm | ±0.1 nm | Slant-range distance |
| ILS LOC | 108.10–111.95 MHz | ~25 nm | ±0.5° | Precision lateral guidance |
| GPS/GNSS | L1: 1575.42 MHz | Global | ±15 m (±1–3 m SBAS) | Precision 3D positioning |
RNAV — Area Navigation
RNAV (Area Navigation) allows aircraft to fly any desired flight path within coverage of ground-based navaids or within the limits of self-contained navigation systems. The aircraft's FMS computes position from multiple inputs (GPS, DME/DME, VOR/DME) and creates virtual waypoints anywhere in space.
- RNP (Required Navigation Performance) adds an integrity monitoring requirement — the system must alert the crew if accuracy falls below the required level
- RNAV 1 — accuracy 1 nm or better, 95% of the time; standard terminal area and SID/STAR procedure
- RNAV 2 — accuracy 2 nm or better; en-route RNAV standard
- RNP AR — Required Navigation Performance with Authorisation Required; allows curved approaches to high-obstacle runways
Course Interception
Intercepting a VOR radial or GPS track from an off-track position is a standard IFR skill. The procedure depends on the angle of interception:
- 30° intercept angle: moderate, predictable intercept — preferred for precision approaches
- 45° intercept angle: standard en-route intercept; CDI responds quickly enough to manage
- 90° intercept angle: fast intercept, used only when far from the track and time is important
- Lead the final turn by approximately 0.5–1 nm for each 10 kt of groundspeed above 100 kt
- An HSI or EFIS navigation display makes course interception significantly easier by showing the aircraft's geometric position relative to the course