Circle of uncertainty
Circle of uncertainty (TP 1102): bounds landmark search once position is unknown. Draw when checking heading and nav log did not resolve the doubt.
| Part | Rule |
|---|---|
| Radius | 10% x distance flown |
| Distance flown | groundspeed x time since last confirmed position |
| Centre | on intended track, that distance along (use track made good instead, if known) |
- Example (TP 1102): 10 min at 120 KT = 20 NM (2 NM a minute), so centre 20 NM along track, radius 2 NM.
- Technique flips: watch ground, match to map (not map first).
- Circle only narrows search. Only positive ID of a distinctive landmark confirms back on track.
Trap: radius = 10% of distance flown (not groundspeed alone, not elapsed time alone), and a radius, not a diameter.
References
- TP 1102 Pilot Navigation, Circle of Uncertainty