Originally Posted by
LASJayhawk
If you are flying level you fly 4 miles to cover 4 miles of ground. In climb or descent you have to fly more than 4 miles to cover 4 miles of ground.
So if you ground speed is the same (ignoring wind) you have higher airspeed in the climb or descent to maintain the same ground speed
Clearly from a non pilot.
Temperature, pressure and thus density altitude all have a big effect in the airspeed/groundspeed relationship. At typical flight angles (even quite large ones) the angular differential is negligible and the above answer does not accurately respond to the question.