Work out top of descent point instantly with clear inputs, formula shown and shareable results.
Top of descent is found by dividing the altitude to lose by the gradient in feet per nautical mile. A 3 degree path is about 318 ft/nm, which is where the pilot rule of thumb 'altitude to lose in thousands of feet times three' comes from.
Top of descent
TOD distance = altitude to lose / (tan(angle) x 6076.12 ft per nm)
Aviation results are planning estimates only. Always verify take-off, landing, fuel, weight and balance figures against the certified Aircraft Flight Manual, current performance charts and applicable aviation regulations before flight.
Three nautical miles per 1,000 ft is 333 ft/nm, very close to the 318 ft/nm of a true 3 degree path, so it is an easy and slightly conservative approximation.
Yes. Most operators add a few miles to slow from cruise speed to approach speed, plus an allowance for a tailwind.