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Glide to shore

Asked by: 923 views General Aviation

How do I calculate altitude that provides adequate glide to shore when crossing a large body of water such as lake Michigan? Distance is 25NM over water. Cruising at 6K' over land, what altitude should I climb to to make sure I can glide to shore while over water and how do I figure wind into the scenario? Thanks!

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2 Answers



  1. Mark Kolber on Sep 30, 2023

    Do you have a GPS or EFB the provides a glide ring?

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  2. Best Answer


    Jeff Baum on Sep 30, 2023

    Depends on the glide ratio of the specific airplane.

    But first, from what I’m seeing, most of Lake Michigan requires a crossing of much more that 25nm. More like 50nm and more.

    But, staying with your scenario of a crossing of 25nm and No Wind…

    The Cessna 172 POH shows a 9:1 glide ratio and has a chart. A 1/2 of 25 is 12.5nm. The chart shows that a minimum altitude needed to glide 12.5nm would be about 8400 AGL (or would that be AWL?). Done the math; 12.5 nautical miles equals 75,950 feet, that divided by 9 (a 9:1 glide ratio) comes up with a minimum altitude of 8,439. (To glide 25nm [1/2 of 50nm] would require a minimum of 16,878)

    The Beechcraft V35B Bonanza has a glide ratio of 10.3:1, this results in a minimum altitude to make 12.5nm of 7,374 AWL. (To glide 25nm [1/2 of 50nm] would require an minimum of 14,748)

    If you’re going to try to add wind into your calculations the easiest is the same as your normal cross country planning for calculating True and Ground Speed. Calculate your True Airspeed from your indicated Best Glide speed. Calculate your glide duration by deciding your Above Water Altitude by the Best Glide Rate of Descent. Next, calculate your Ground Speed for the headwind and tailwind component. Now, you will be able to determine the change-over point between continuing or returning to the shore behind (don’t forget to take into account the altitude loss during the turn, and a fudge factor for imperfect IAS control and less that book performance).

    As Mark points out, if your system can take into account the wind effects, the EFB/FMC with a glide ring is far easier.

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