NavList:

David C you wrote: “I now follow the Australia/NZ to Santiago air route. As it is nearly east-west it is probably not the best of routes to study mercator sailing”

That’s true.  Just looking at the Flight Track Map for QFA28 B789 (VH-ZNL) Santiago to Sydney 22Dec2024 on FR24, which appears close to Mercator projection, The aircraft, which is probably flying a great circle, appears to trace the cross section of a bathtub.  However, if you could maintain modern day speed range and endurance but only had the air navigation resources available in the 1950s, you could use Mercator sailings and still make a good approximation to a great circle by splitting the trip from Sidney to Santiago into three parts, a South Easterly Section, followed by an Easterly Section, followed by a North Easterly Section.   We regularly did something similar flying between Waddington, Lincolnshire and Goose Bay Labrador, except we used a protractor and dividers instead of Meridional Parts.  DaveP