Descent Rate & Angle Required Calculator
Work out the vertical speed needed to lose a given altitude over a given distance at your ground speed, the resulting descent angle, the distance and time to descend, and the 3-degree glidepath rate (ground speed × 5) with a table of rates by ground speed.
How it works
Time = distance ÷ ground speed; ROD = altitude ÷ time; angle = atan(altitude ÷ (distance × 6,076)); 3° ROD ≈ GS × 5; start distance (NM) = altitude ÷ tan(angle) ÷ 6,076
Descent planning is triangle geometry: altitude to lose is the vertical leg, distance to the fix is the horizontal leg, and ground speed sets how quickly the horizontal leg is covered — so the vertical speed required is altitude divided by time. The standard 3° glidepath is around 318 ft per nautical mile, which at any ground speed works out to about five times the ground speed in feet per minute — the rule every instrument pilot memorises. Because it is ground speed that matters, a tailwind on descent demands a higher rate or an earlier start, and the classic "three times the altitude" rule for top of descent should be padded for deceleration and for the wind.
Worked example
Losing 8,000 ft in 25 NM at 140 kt gives 10.7 minutes, so 747 ft/min at a 3.0° angle — a normal profile. A pure 3° path at that speed is 700 ft/min and needs 25.1 NM; at 200 kt the same 3° needs 1,000 ft/min.
Frequently asked questions
Why does the required rate depend on ground speed, not airspeed?
Because the distance to the fix is over the ground. A 30 kt tailwind at 140 kt TAS means 170 kt GS — 21% less time — and the rate must rise from 700 to 850 ft/min for the same 3° path.
What descent angle is used on approaches?
ILS and most RNAV glidepaths are 3.0°; obstacle-limited approaches go to 3.5–4.5°; London City is 5.5°. Non-precision step-downs are often flown as a continuous 3° descent using the ×5 rule.
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Planning aid using standard flight-training rules of thumb and ISA atmosphere approximations — not a substitute for the aircraft flight manual (AFM/POH) performance charts, ATC instructions or an approved flight computer. Always apply the manufacturer's data and required safety margins.