Intruder
The circumfrence of the earth is (in 'round' numbers) about 21,600 NM (360 deg * 60 NM per deg). Divide by 2*PI, and the radius is about 3437.746771 NM.
Add 6nm (altitude 36000ft) to radius giving 3443.746771 NM. Multiply by 2pi giving circumference of 21637.6991131943440470267223105866 need I go on with the decimal places????
Calculation was based on the figures you provided
How have you managed a different answer?!? "One" would have thought all those bloody decimal places would have IMPROVED accuracy???
Andy