Originally Posted by The SSK
I would imagine the rule of thumb is to have the maximum cabin width round about where the passengers' shoulders would be. This would tend to put the floor close to half-way up the cross-section on a larger aircraft, but proportionately closer to the bottom of the hull on a smaller one.
Sure, it works for most main decks.
But Boeing 747 upper deck has the maximum width at floor. It then narrows rather steeply upwards. Nevertheless B747 has the upper deck.
And a lower deck is possible: see this
http://www.!!!!!!!!!!!!!!/open.file/0136897/M/ So, can anyone explain just why the Tristar lower deck was so unacceptable?