Passenger Planes: Boeing 747

Initial designs of the 747 called for a twin deck aircraft, with two decks running the full length of the fuselage. This gave a very effective increase in capacity, however, the ability to evacuate two decks of passengers was found to be not possible within the recommended 90 second limit. Boeing opted for a single main deck which was then widened from the standard economy configuration of the day of three and three with a single aisle, to a twin aisle layout with seating in three four three.