Time, Speed, Distance + 1-in-60 Rule
This lesson combines the basic formula of motion with the most important mental rule of thumb for PPL cross-country.
Basic formula
Distance = speed × time
In navigation units:
- D in NM
- v in kt (= NM/h)
- t in hours
Rearranged:
- t = D / v
- v = D / t
Conversions minutes ↔ hours
| Time | Fraction of hour |
|---|---|
| 1 min | 1/60 h |
| 6 min | 0.1 h |
| 10 min | 1/6 h |
| 15 min | 0.25 h |
| 30 min | 0.5 h |
Rule of thumb: in 6 min, an aircraft covers GS/10 NM. Example GS = 90 kt → 6 min ≈ 9 NM.
Worked example
- D = 75 NM, GS = 100 kt → t = 75 / 100 = 0.75 h = 45 min.
- t = 12 min = 0.2 h, GS = 110 kt → D = 110 × 0.2 = 22 NM.
The 1-in-60 rule
From geometry: for a 60 NM chord in a 1° sector, the lateral displacement at the far end is 1 NM.
Application 1: track error correction If after a distance Df (NM "flown") you find yourself Do NM from the desired track, the track-error angle is:
TE (°) ≈ (Do × 60) / Df
Application 2: closing angle To rejoin the target point within the remaining distance Dr, the closing angle is:
CA (°) ≈ (Do × 60) / Dr
Total correction (add to heading, sign per side of off-track):
Total correction = TE + CA
Worked example for the 1-in-60 rule
Plan: 80 NM leg EDDM → EDQS. After 30 NM you determine by visual nav: 4 NM right of plan track.
- Df (flown) = 30 NM
- Do (off-track) = 4 NM right
- Dr (remaining) = 80 − 30 = 50 NM
TE = (4 × 60) / 30 = 8° — pilot drifted 8° too far right. CA = (4 × 60) / 50 = 4.8° — to reach destination in 50 NM.
Correction (heading left): 8° + 4.8° ≈ 13° left.
→ If previous heading 090°: new heading 090° − 13° = 077°.
Rule of thumb for 6 NM marks
In practice 6 NM marks are often used instead of 60 NM:
- TE (°) ≈ (Do in NM × 60) / (Df in NM)
- For Df = 6 NM: TE = 10 × Do (in NM).
- For Df = 12 NM: TE = 5 × Do.
Visualisation
Picture yourself at the start point drawing a fan of 1° rays. After 60 NM, ray spacing is 1 NM/ray. After 120 NM 2 NM/ray. After 30 NM 0.5 NM/ray.
Cross-reference to PLOG
The 1-in-60 rule is the mental tool for in-flight track correction without picking up the plotter. The PLOG usually has pre-computed heading and position updates every 10 or 20 NM.