A plane flies from A (60°N, 40°W) to town B (60°N, 140°E)

Answer 1

What is your question?

Answer 2

since the towns are at the same latitude, the radius of the circle flown is Rcos60 = 1/2 earth radius
so the distance flown is s = rθ = R/2 * (140+60)/360 * 2π

unless the plane flies along a great circle ...

Answer 3

yes I response to maths