The Excel GreatCircleDistance function returns the line-of-flight distance between two latitude-longitude pairs.
=GreatCircleDistance(lat1, long1, lat2, long2)
lat1, long1 are the coordinates of the origin
lat2, long2 are the coordinates of the destination
=GreatCircleDistance(1,2,3,4) returns 5
The results are accurate to better than 0.5mm for all cases except those where Haversine is used. These all occur at longitudes between -179.5 and 179.5, which are in the middle of the Pacific.