Required Descent Rate Calculator (Crossing Restrictions)
“Cross 30 miles out at 11,000” solved: the descent rate and angle the restriction demands from your present position — and whether it's still flyable.
The counterintuitive lever: slowing down REDUCES the required rate (more minutes to the fix) even though the angle stays fixed. Speed brakes change the angle; the throttle changes the time. Different problems, different tools.
Formula
⚠️ For flight planning and education only — verify with current charts, AFM and ATC clearances. Not for primary navigation.
“Cross 30 miles out at 11,000” solved: the descent rate and angle the restriction demands from your present position — and whether it's still flyable.
About Required Descent Rate Calculator (Crossing Restrictions)
“Cross BAYST at one-one-thousand” converts instantly into a rate problem: feet to lose over minutes remaining, with the minutes shrinking at your ground speed. This calculator solves it from present position — required ft/min, the implied path angle, and a verdict with the two escape levers explained (slowing buys time and lowers the rate; drag steepens the achievable angle) — plus the sentence to use when neither suffices.
How to use Required Descent Rate Calculator (Crossing Restrictions)
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula rate = altitude-to-lose ÷ time-to-fix; angle = atan(Δalt / (dist × 6076)) substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Required Descent Rate Calculator (Crossing Restrictions)?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula rate = altitude-to-lose ÷ time-to-fix; angle = atan(Δalt / (dist × 6076)) with sources cited on the page
- ✓The counterintuitive lever: slowing down REDUCES the required rate (more minutes to the fix) even though the angle stays fixed. Speed brakes change the angle; the throttle changes the time. Different problems, different tools.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
Why does slowing down make a crossing restriction easier?+
The restriction fixes the geometry (feet over miles) but your VSI flies feet over MINUTES — and slowing stretches the minutes: 6,000 ft over 18 nm needs 1,167 fpm at 210 kt but only 933 at 168. The angle didn't change; your time budget did. It's the single most underused lever in GA descent management, mostly because the instinct under pressure is to hurry.
At what required rate should I get concerned?+
Bands for unpressurized GA: under 1,000 fpm is routine; 1,000–1,500 is brisk but fine briefly; beyond 1,500 sustained, ears, engine cooling (shock-cooling debates aside, big power reductions) and the approaching-unstable trend all argue for action — slow, drag, or renegotiate. Jets ride higher numbers comfortably but face their own idle-path and speed-limit ceilings.
What does 'descend via' add to this arithmetic?+
A chain of restrictions: descend-via clearances on STARs make you responsible for meeting every published crossing altitude/speed in sequence — effectively running this calculator fix-to-fix down the arrival. FMS VNAV does it continuously; the mental version is checking the next restriction's required rate each time you cross one. One unmakeable link means saying so before it, not at it.
How do I phrase it when the restriction isn't makeable?+
Early and factually: 'N123AB, unable to cross BAYST at one-one-thousand — request lower now' (or 'request vectors for descent'). ATC's alternatives are easy ten miles early and hard at the fix. The phrase carries no penalty; arriving high and diving for it carries several, starting with an unstable approach and ending with the letters that follow one.
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