Lol, was wondering about that. Figured They removed the prop for working in close like that.
Was reading up on the B-17, they said the wings were so big they could walk in them. Then go up to the engines in flight and do some minor service and tuning as needed while underway.
Really interesting article about them, their prodution, how they outfitted them, and the war efforts they were used in.
Crew members had to be tough.