Use the formula d = 1.22√x, where x is the elevation, in feet., of a person, to estimate how many miles a person can see from an airliner at 12,100 feet.

Question

The person can see blank miles from the airliner at 12,100 feet. (Type an integer or a decimal).

I got 134.2 miles. Would that be correct?

Answer 1

Hi Tor P.,

Your calculation is right as far as you took it. But you need to round the result to the # significant digits in the formula, which seems to be 3, from both the "1.22" and the "12100" pieces. The extraction of the square root, and the multiplication, don't affect the use of significant digits method of rounding. If you step up a level to consider variances (assuming the 12100 to be measured to +-50 ft), then you need to propagate variance correctly. That's quite another discussion, however.

And not a useful one, here: you are only dealing with an approximation, when you actually have a trig function you are invoking! And then there's the distinction, are you measuring line-of-sight, or along the Earth's surface from the point directly below you?

And lastly, what do you mean by "seeing"? You won't be able to distinguish much on the ground, at a distance of 134 miles. Even in clear air, which seldom obtains!

--Cheers, --M. d.