NavList:

Dear Peter and Lars,

Excellent example from you Peter and excellent explanation from you Lars.

-If you follow a great circle from one Departure Point (e.g. Санкт-Петербу́рг) at a given Departure Track Heading and over a given Distance you will eventually hit your arrival point, which is unique.

- But this does not imply the existence of only one such unique/single Departure Point with both same Departure Track Heading and Distance to hit this very same unique arrival point !

Since we do not have accurate enough azimuth references on board most craft, we are - or maybe better : at least I am - insufficiently familiar with Equal Azimuth Lines.

Peter, we have here an excellent example of an Equal Azimuth Line (030° towards one unique arrival point) having 2 different intersections with a circle of equal altitudes centered on that same and unique arrival point.

I really learnt something here.

Thanks also and again to you Dave for having given us this example to study.

Best Regards,

Antoine