Verify before flight. Check the POH/AFM for aircraft-specific limits and performance.
Flight Planning
Top of Descent Calculator
Estimate descent distance using altitude to lose and desired descent gradient.
ft
ft/NM
kt
TOD distance—
Required descent rate—
Descent time—
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Losing 6,000 feet at 300 ft/NM
Losing 6,000 ft at 300 ft/NM requires 20 NM. At 120 kt groundspeed, that takes 10 minutes and requires 600 fpm.
Include distance for deceleration or leveling off separately. The selected gradient is a planning assumption; terrain, clearances and published restrictions control descent.
Formula and method
Top-of-descent distance = altitude to lose ÷ selected descent gradient. Descent time then follows from groundspeed.