Descent + Deceleration Planner
The miles slowing down steals: TOD computed with the level deceleration segment the basic 3-to-1 forgets — cruise speed to approach speed, honestly.
Slippery airplanes don't slow downhill — the decel segment is flown level (or nearly) and costs real miles: 60 knots of speed reduction is 5–7 nm in a clean single, more in anything faster. The rule of thumb hiding here: a mile per ten knots.
Formula
⚠️ For flight planning and education only — verify with current charts, AFM and ATC clearances. Not for primary navigation.
The miles slowing down steals: TOD computed with the level deceleration segment the basic 3-to-1 forgets — cruise speed to approach speed, honestly.
About Descent + Deceleration Planner
The 3-to-1 rule delivers you to pattern altitude — at cruise speed, which is the wrong arrival twice over. Clean airframes barely decelerate downhill, so the speed has to come off level, and level miles must be budgeted: roughly one per ten knots in a light single. This planner adds that deceleration segment to the standard descent math, producing the honest TOD that has you at both the altitude AND the speed when the airport arrives.
How to use Descent + Deceleration Planner
- 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 TOD = 3-to-1 descent miles + (speed to lose ÷ decel rate) — the decel happens level or shallow substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Descent + Deceleration Planner?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula TOD = 3-to-1 descent miles + (speed to lose ÷ decel rate) — the decel happens level or shallow with sources cited on the page
- ✓Slippery airplanes don't slow downhill — the decel segment is flown level (or nearly) and costs real miles: 60 knots of speed reduction is 5–7 nm in a clean single, more in anything faster. The rule of thumb hiding here: a mile per ten knots.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
Why won't my airplane slow down while descending?+
Energy bookkeeping: descending converts altitude to airspeed unless drag absorbs it, and clean modern airframes are drag-poor by design. Pointing down at fixed power, speed rises toward the trim equilibrium. To descend AND decelerate simultaneously needs the drag budget raised — power to idle, eventually flaps/gear — or the deceleration scheduled level, which is what this tool budgets.
How many miles does slowing actually take?+
Level, power reduced to approach setting: light trainers shed 8–12 kt per nm (already draggy), slick singles and light twins 6–10, jets far less (hence their elaborate decel planning). The bundled rule — a mile per ten knots — sits safely inside most GA numbers. Measure yours once: note the distance a 40-kt level reduction takes, and you've calibrated the input this tool wants.
Where should the decel segment sit in the arrival?+
At the bottom, mostly: descend at cruise-ish speed (efficient, expedites for ATC), then level at pattern/initial altitude with the budgeted miles remaining for the slowdown. The alternative — slowing first, descending slow — wastes time aloft but suits turbulence (maneuvering speed logic) and steep terrain arrivals. Either way the miles are paid; the choice is where.
How does this interact with crossing restrictions that include speeds?+
'Cross at 11,000 and 210 knots' makes the decel segment part of the restriction: the FMS plans deceleration before the fix, stealing miles from the descent and steepening what remains — why descend-via profiles feel busier than plain altitudes. Mentally: apply this tool's logic at each speed-restricted fix, budgeting the mile-per-ten-knots BEFORE it, not after.
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