Mental DR Rules of Thumb for PPL Practice
In the cockpit there is no time for long calculations. This lesson collects time-tested rules of thumb that suffice at PPL level and can be done in the head.
Wind components ("clock code")
Wind comes from a specific direction relative to track. Components can be estimated from this table (based on cos and sin at standard angles):
| Wind angle to track | Headwind/tailwind fraction | Crosswind fraction |
|---|---|---|
| 0° / 180° | 100 % | 0 % |
| 30° / 150° | 87 % | 50 % |
| 45° / 135° | 71 % | 71 % |
| 60° / 120° | 50 % | 87 % |
| 90° | 0 % | 100 % |
Example: wind 30 kt from 045°, planned track 090°. Angle: 045°. Crosswind component ≈ 30 × 0.71 ≈ 21 kt from the left. Headwind ≈ 21 kt.
Wind correction angle (WCA) — quick estimate
Rule:
WCA ≈ (crosswind component × 60) / TAS
(more precisely: sin(WCA) = XW/TAS, roughly linear for small angles).
Example: TAS 100 kt, crosswind 15 kt → WCA ≈ (15 × 60) / 100 = 9°.
Time from distance
"GS / 6 in NM per 10 minutes": at GS 90 kt → 9 NM in 6 min, 15 NM in 10 min.
| GS (kt) | Distance per 6 min | Distance per 10 min |
|---|---|---|
| 60 | 6 NM | 10 NM |
| 90 | 9 NM | 15 NM |
| 100 | 10 NM | 16.7 NM |
| 120 | 12 NM | 20 NM |
| 150 | 15 NM | 25 NM |
| 180 | 18 NM | 30 NM |
Time from arc length
1° of longitude in 6 seconds at GS 60 kt at the equator (i.e. 1 NM in 1 min) — rarely used, but a good sanity check.
1-in-60 rule — cockpit short form
For off-track distance Do after flown distance Df:
Correction (°) ≈ (Do/Df) × 60
and the double rule: correct twice — once for heading correction and once for closing angle.
Rule of thumb for even distribution: with short remaining distance → double the correction.
Climb / sink rate
- Climb gradient in % = (climb rate fpm × 60) / GS in kt × 100 / 6076
- Simplification: at 100 kt GS and 500 fpm → gradient ≈ 5 %.
- Rule of thumb: climb in ft/NM = (climb fpm × 60) / GS in kt. At 500 fpm and 100 kt: 500 × 60 / 100 = 300 ft/NM.
Sink gradient for PPL (3° approach standard)
3° descent = 300 ft per NM (≈ 5 %).
- At GS 90 kt: 90 NM/h → 90 × 300 = 27,000 ft/h = 450 fpm. Rule: sink rate fpm = 5 × GS in kt for 3° approach.
- At GS 120 kt → 600 fpm.
Fuel (see next lesson)
Rule of thumb fuel burn × hours + reserve.
Sense check in storm
If the wind to track is > 100° (i.e. from the rear hemisphere), HW becomes TW. At exactly 90° zero longitudinal component — pure crosswind.