Estimating glide range (windshield method)
Flying off best glide speed shortens glide distance. TP 1102 example: 6,000 ft AGL, still air, best glide 70 KT:
| Speed | Range | Why |
|---|---|---|
| 70 KT (best glide) | 10 NM | Reference case |
| 60 KT | Short of 10 NM | Rate of descent only slightly lower |
| 55 KT | Under 4 NM | L/D deteriorates: rate of descent rises far more than speed drops |
Wind:
- Shifts best-range airspeed (see range-endurance).
- Wind-corrected speed too complex in an emergency: fly familiar still-air best glide speed. Read range visually, do not compute it (TP 1102).
Windshield reference method: pick a fixed, repeatable windshield point (glass mark, spot beside compass). Watch the ground point against it:
| Ground point vs. windshield point | Meaning |
|---|---|
| Moves down | Reachable, height to spare |
| Stays stationary | Aircraft reaches this spot |
| Moves up | Unreachable |
Ground point judged (TP 1102):
- Aerodrome: point of flare
- Forced landing: touchdown point
Trap: method valid only when stabilized (constant power or power-off, attitude, airspeed); changing any resets the picture.
References
- TP 1102 Ex.8 Descending, Estimating Range