Ive gotten a bit hooked on viewing in-flight aircraft with binoculars from the ground. Myself and a few friends are wondering, given the value of all of us standing at an elevation of sea-level, and generally clear sky conditions, what is the greatest physical distance from us as the aircraft “disappears” out of sight over the horizon? We’ll just say the aircraft is at an altitude of 360. There are many particular values that could obviously be tweaked, but just a general answer, anyone?

# Aircraft distance from sea level...

**magnetoz**#2

I did a Google search for distance to horizon and found the equation of 1.17 times the square root of the altitude.

In this example, roughly 260 miles if you are at sea level and the plane is at 36,000 MSL

**emathieu**#3

Wow that is very interesting. Being a novice with ‘plane watching’ I never took the time to understand the distance a plane is visible, thanks for sharing the information!

**simpilot7**#4

Kudos for the info Mag…thats some interesting stuff, esp for us novice “regular job by day, aviation freak by night” folk. thanks!

**tobyz1**#5

You can turn that question around and ask how far up/down the coastline could the passengers of a trans-oceanic flight see from an altitude of 36,000 MSL. 260 miles! Since the pilot can see in both directions, he has a visual ‘wingspan’ of 520 miles. Quite a horizon for him!

**dcgreene**#6

Well, taking the BoatSafe.com formula at face value (and I’m a little reluctant to jump in here, but) …

The square root of 36,000 is 189.74 (rounded to 2 decimal points).

189.74 X 1.17 = 222 (rounded to 2 decimal points) nautical miles.

Now, to convert to statute miles …

222 X 1.15 = 255.30 or about 260 statute miles as **magnetoz** posted.

I just thought the nautical to statute mile conversion should be made evident.

**NeedleNose**#7

I was lookin’ at that earlier and noticed the discrepancy. I was wondering about that, but not too concerned about it. Thanks for clearing that up.