What about cruise on 10hr+ flight?
Probably the only time it is "allowable" is on long overwater sectors but even so only if it's co-ordinated in a similar manner to controlled rest/controlled napping...i.e. one pilot monitoring the ship
and ATC, allowing the other pilot to go "off watch" for a short while.
So you have never tuned the HF or ADF to a radio station?
Problem is finding anything audible or worth listening to at 50 west or east.........