Hi,

In article ,
Bertie the wrote:
Well, even at middling altitudes I find it hard to tell the altitude of
other airplanes.

I read somewhere that if the other plane appears above the horizon, it's
above you. Similarly, if it appears below the horizon, it's below you.

Obviously this will change depending on whether you're climbing or
descending, but as a general rule it sounds like it could make sense.

Haven't really had the chance to test it myself since I read it though.

Andy