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3 Answers

Top of descent

Asked by: 5621 views , ,
Commercial Pilot, Flight Instructor, General Aviation, Instrument Rating, Private Pilot, Student Pilot

Please could someone provide me with an easy rule of thumb/ formula for top of descent for a private pilot. There seems to be no standard formula and some of them out there and have no explanation. Thanks in advance!

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3 Answers



  1. John D Collins on Aug 04, 2015

    With modern GPS avionics, the time remaining to your destination is readily available. If you know your altitude above the airport pattern altitude, you know how many thousands of feet you need to lose. Double the number of 1000’s of feet you need to lose and use this as the time remaining in minutes when you wish to start your descent. So my home airport has a 1500 foot traffic pattern and if I am at 8500 feet, then I need to lose 7000 feet from cruise to pattern altitude, Double 7 is 14 minutes. I often add an extra minute so I can be at pattern altitude well before joining the pattern. This time assumes you will use 500 feet per minute of descent. So I would start down when I am 15 minutes from my home airport.

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  2. Dan S. on Aug 04, 2015

    If you want to use mileage from airport to start descent in a typical single, determine thousands of feet to descend to pattern altitude. Using Johns’s example, 7*2=14 and at 2 miles per minute, start descent 24 miles from the airport. I’ll usually add 1 mile as buffer.
    If you ever fly faster aircraft, 3 times the altitude to lose in thousands of feet works pretty well. With 30,000 feet to lose, multiply 30*3, you would need to start down around 90 miles from destination.

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  3. Mark Kolber on Aug 05, 2015

    If you want an explanation of John’s formula, a generally accepted descent rate for a non-pressuruzed piston aircraft is 500 feet per minute. It is a rate that is comfortable for most passengers, not producing too rapid changes in pressurization.

    The rest is simple math to get the time away from destination and Dan’s addition simple math to convert the time to a distance based on speed.

    You can see multiple variations on the theme, most of which are simply using arithmetic shortcuts to make the math simpler. As an example, take John’s 7000 altitude loss and notice that 7000/500 and 7×2 give the same result.

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