Always thought it was based on maritime law, where ships pass port-to-port, the captain sitting on the port side to maintain visual contact with the other ship when passing. Which doesn't explain why so many pleasure craft are built these days with the pilothouse to starboard, even though maritime law still mandates ships pass "to each other's right", just as aeronautical law says.
Probably me that has missed something but if ships pass 'port to port' then are they not keeping each other on
their left?
