Position Fixing
Position fixing = determination of own position at a given time with sufficient accuracy to base navigation decisions on it.
Types of position fix
1. Visual direct overhead
Directly overhead the landmark — accuracy ±0.5 NM.
- Best method for PPL practice.
- Required: unambiguously identifiable point (aerodrome, reservoir, castle).
- Note time and altitude in the PLOG.
2. Visual bearing on two landmarks
Two or more landmarks in known direction → intersection gives position.
- Accuracy ±1–3 NM (depending on distance and angle between bearings).
- Useful with valleys, hills, river bends.
3. Radio bearing
With two VOR stations (cross cut): pilot tunes two VORs, reads each radial → intersection of the two radials is the position.
- Accuracy ±2–5 NM at 60 NM distance, worse at large distances or sharp angles.
- Best: bearing intersection 60°–120°.
- Subject 060 lesson "VOR" explains the technique in detail.
With DME: intersection of a VOR radial and a DME distance.
- Unambiguous in symmetric setups.
- More accurate than pure VOR cross-cut (DME distance is exact).
4. NDB bearing (ADF)
With two NDBs: similar to VOR cross-cut, but NDB bearings are less accurate (magnetic vs. true, atmospheric disturbances).
- Accuracy ±5–10°, leading to several NM error at long distances.
5. GNSS / GPS
Direct position from satellite receiver.
- Accuracy: typically 1–3 m with clear view of at least 4 satellites (civil L1).
- With SBAS (EGNOS in Europe, WAAS in USA): < 1 m.
- Standard for modern cockpits and EFBs.
- Subject 060 lesson "GNSS" details.
6. ILS / GPS approach
Vertical + horizontal guidance on approach — very precise in the approach area.
- Not intended for cross-country navigation outside the approach area.
What to record?
Per position fix:
- Position (LAT/LON or known point name)
- Time (UTC)
- Altitude (AMSL)
- Heading / track
- GS (from time between last and current fix)
- Possibly fuel on board (FOB)
Fix frequency
- PPL VFR recommendation: every 10–15 min or at each planned waypoint.
- In bad weather or over uniform terrain: more often (5 min).
- In good weather, familiar terrain: 20 min may suffice.
Use of fix data
- Check GS → verify wind correction.
- Measure track offset → 1-in-60 correction.
- Compute ETA (remaining distance / GS).
- Check fuel status.