Charlie - I'm off to read your link now. Hope it's not going to do my head in too much!
Completely agree with Circuit Basher, by the way, about the "classical" solution only being an approximation, which is why I said it wouldn't work over long distances or near the poles. But a further thought occurs to me. Budipro specified that the aircraft's direction was given as an angle from north, implying that he's flying a rhumb line. But in the situations where "classical" maths breaks down (long distances or polar transits) you wouldn't do that anyway - you'd either fly a great circle, or for polar transits you may use grid navigation. In either case, your track will be far from constant, so the question isn't valid anyway! (Wonder if Charlie's link will address these issues.....)
FFF
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