Obsolete in a very peculiar way

This thing had "passageways inside the wings so crewmembers could service the engines in flight." Service what? What on earth could you reach and service in a crawl space at the rear of the engine that would matter in keeping the plane flying in an emergency? "Hold my parachute, Bob, I'm gonna replace the spark plugs on cylinder eight of engine three." Can somebody clue me in? I've always wondered about this after reading about several other (earlier) aircraft having same.


Photo credit: James Vaughan - Flickr - X-Ray Delta One

View: https://youtu.be/2LSOiep6GCA?feature=shared

They might have advertised access to engines and systems in-flight for wow-factor, but I think it was more for normal servicing access in there. However, things like oil tank replenishment in flight might have been needed, until remote pumping was designed.

Eng

A remote possibility was access to things like air pump/s or vacuum pumps, Hydraulic pump/s, generator/s.
This assumes there are spares on board and/or problem is minor like loose fittings/connections?
But still a daunting task in dark with a flashlight with even the neighboring engine roaring away.

That said, some of the 1920s/early 30s record flights were accomplished with inflight repairs and without that sissy crawl tunnel. Real men climbed across the wing from strut to strut and tied themselves in place to work on the engine

Well, you can turn the engine off so that it is not running when you service it. In some engines the magnetos are in the back and could be reached from inside the wing. Aside from that, you can have instrumentation back there you can read that is not available in the cockpit. On aircraft such as the Ford Trimotor, there were some gauges mounted right on the engine you had to read by looking at them through the window. You also can add oil.

The PBY had a the flight engineer's compartment in the pylon that supported the wing, so it was close to the engines.

I recall one flight on a DC-9 where I was seated next to an engine; the side of it was the only thing visible through the window. It occurred to me that they really ought to provide the passenger in that position with some engine instrumentation so he could make the decision to move in case things looked about to come unzipped.

B-36A Info Below.

Cool picture of Dornier X showing the tunnel in the wing.

View: https://www.reddit.com/r/WeirdWings/comments/s6a3dv/cutaway_of_a_dornier_do_x_one_of_the_mightiest/#lightbox