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The initial great-circle course between two positions comes from the spherical bearing formula, and the distance from the haversine formula using a mean Earth radius of 3440.065 nautical miles. On a long leg the course changes continuously, so the final course differs from the initial one.
Great-circle course
theta = atan2(sin(dLon) x cos(lat2), cos(lat1) x sin(lat2) - sin(lat1) x cos(lat2) x cos(dLon))
Aviation results are planning estimates only. Always verify take-off, landing, fuel, weight and balance figures against the certified Aircraft Flight Manual, current performance charts and applicable aviation regulations before flight.
A great circle crosses each meridian at a different angle. Only tracks along the equator or a meridian keep a constant true course.
No. A rhumb line holds a constant course but is longer. The great circle is the shortest path and is what long-range navigation systems fly.