NavList:

Sam you wrote:  To find the new Latitude use the Hc formula but for declination use the arcosine of the distance travelled divided by the radius of the earth in nm.  LHA is course bearing.  Ap Lat. is the Latitude of origin.  To find the Longitude use the typical formula to obtain Zn with the Latitude, obtained above, as the Hc.  Once you get the answer, subtract or add it to Longitude of origin.  Mathematically there has to be some way to determine whether to subtract or add the result from the Longitude of origin. This probably needs some refinement....but for the moment it worked.

I think I see what you’re doing.  You’re effectively substituting the start and finish points as two corners of a skewd PZX triangle and the distance between them as the side joining them – noble stuff, but pretty complicated and a bit beyond my powers of comprehension at 00.08.  I think I’ll stick with my method with a Douglas protractor, albeit ‘flat Earth’.  W.r.t. how to deal with the sense of chlong, why not just visualise it (or write a condition)?  If course is in the sector 360 through 090 to 180, the destination longitude will be east of the start point, and if it’s in the sector 180 through 270 to 360 it’s west of the start point.  DaveP