By the late 1930’s the Boeing 314 flying boat became the standard of luxury air travel.

In the hangar for maintenance.

The 314 had access to the engines by crawling out through the wing so they could be serviced while in-flight.

What I like about these photos is that Walter had to be standing on the wing to take them.

See that open hatch?  That’s his return through the wing and to the main deck.