Aviation Rules of Thumb

M 0.80 at tropopause = approx. 450 knots. Time to fly any distance at 450 knots groundspeed can be found easily...just take the distance (NM), divide it by 10...take 1/3 of the result, & add the two. This is time in minutes to fly the given distance.

example: 360 nm to fly -- divided by 10, equals 36. 1/3 of 36 = 12, 45+12 = 57. It will take 57 minutes to fly the distance.