I’m currently spending some time with the Boeing 247D, for reasons which can become apparent later, and I found that the text has a minor error in it. The specs for the Boeing on page 386 lists it as having 12 seats on board, but being able to carry 5 passengers (in addition to the pilot and navigator).
First of all, as near as I can tell the 247D actually had five rows of two seats, for a total of 10 passengers, as shown above. So even if it was fitted for passenger flight, it wouldn’t hold 12 plus pilot and navigator. Moreover while the Boeing’s are configurable, I don’t know how much so once you’re on the ice. The diagram on page 387 shows the Boeing outfitted with four extra fuel tanks just behind the cockpit, which would take up two rows, which leaves six seats.
Once you make room for the ‘extra radio equipment’ listed on page 386, that probably leaves us with the five passenger payload it lists.
Stay tuned for more riveting content!