Altitude of a Landing Airplane

A friend posted that airplanes are going right over her house in their new landing path. I’ve noticed that at my house too, although I live twice as far from the airport as she does.

Technique

How high is that airplane?  A homey technique.

Outside, I extended my right arm when the next jet came overhead. The plane’s length was covered by the tip of my finger to the second knuckle (Figure 1 below).

That gave me similar triangles. One from my eye to my finger, the other from my eye to the plane.

That is, the 2″ of my finger is 2′ from my eye and the 230′ length of the plane is x’ from me.

Thus, 2″/2′ = 230’/x.

With 2″ = 1/6′, 1/12 = 230’/x

Or x = 230′ * 12 = a bit over  2700′

At my house, the airplane is still 1/2 mile up.

Figure 1. Two triangles for altitude estimate

Figure 1. Two triangles for altitude estimate

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