green-dot-speed,
Long Distance over water flying has always used Great Circle Navigation, but until INS, Omega, GPS/IRS etc. came along to enable constant maintainance of the Great Circle Track, The Great Circle was 'broken' into smaller sections, usually about 300 nm apart, and Navigators would fly a Rhumb line between these successive points. Such tracking was known as "Composite Tracking", and some tracks, such as Southern Indian Ocean from Australia to South Africa were published and named as such, i.e. Composite Great Circle / Rhumb Line Track. The advent of INS, Omega, GPS/IRS etc. enabled pilots to fly constant Great Circle Tracks, and forced the Navigators into retirement.
What can be fairly misleading on a great deal of the North Atlantic routes is that Magnetic Variation change fairly nicely disguises the actual constant change in True Track, making them APPEAR to be Rhumb Lines. For the example quoted earlier (40N20W to 43N30W), the Initial Track, Distance, and Final Tracks are -
295.1°(T) / 483.7 nm / 288.5°(T), clearly showing a 6.6° Track change, or a 1° Track change every 73 miles.
If you consider the Initial and Final Magnetic Variation to be applied (9.40°W and 14.26°W), the same track becomes -
304°(M) / 483.7 nm / 303°(M), which does look very close to being a Rhumb Line, but is NOT.
411A, the last time that I used Pressure Pattern Navigation was on a DC 4, I must be showing my age
It did work well, wandering all over the sky from MPP to MPP, but magically arriving very close to the destination
I suspect not so suitable for today's congested airways.
Regards,
Old Smokey