Don't know about the 30s but when I started in 1955 there were no SIDs, STARs or TAPs. I seem to remember that a guy called Jeppesen was makin a few sketches and notes as he flew around the States. RAF EnRoute charts started circa 1961. So I suspect the 1930s were using topographical maps, astro when it was dark and suck-it-and-see on arrival (Look at the signal square). No let down aids either. (Find a gap or keep a very good eye on Safety Alt.) A good reason to use seaplanes on the Imperial route.
Later thought; Don't know when NDBs started?
Last edited by Four Turbo; 8th Mar 2022 at 10:36.
Reason: Later thought