Whats the closest distance I can see from the track of an airliner while in the flight levels? From my estimates it’s about 2.5 to 5 nm. Next time I’m flying I’ll bring a sectional with me and find out what it actuall is.

In the above:

Lines “a” and “b” are parallel,

lines “g” and “e” are parallel,

lines “e” and “g” are perpendicular to lines “a” and “b”,

angle DAE is equal to angle FAG,

the distance of AF is 13 in (+/- 2 in),

the distance of FG is 8 in (+/- 2 in),

point “A” is where your eye is.