Departure

Question 1

Departure(at the equator) =

Answer 1

change in longitude x 60

Question 2

Departure(away from equator) =

Answer 2

(change in longitude x 60) x cos latitude

Question 3

An aircraft flies a distance of 1200nm at lat 30° and lat 0°. What is the change of longitude of both scenarios?

Answer 3

Since one nautical mile is defined as the amount of distance travelled along 1 minute of latitude(along a meridian), 1° of latitude will equal 60nm. Remember that this is only correct along a meridian or along a parallel of latitude at the equator(000° LAT)

Travelling 60nm on a parallel of latitude away from the equator will result in a greater longitude change. And a given longitude change will result in less distance travelled. Remember that the nautical mile is defined along a meridian(N/S)

1° of latitude along a meridian will equal 60nm

1° of longitude will only equal 60nm at the equator.

So, 1200nm at the 0° lat will equal:

1200/60 = 20° of longitude change.

1200nm at 30° lat will then have to equal a greater amount of longitude change:

1200/cos 30° = 1385

1385 / 60 = change of longitude of 23°.