America West - Check your facts. The 747-400 does not have a spiral staircase but rather the standard type at door 2L.
Boeing has certified the capacity of the upper deck in the following manner :
741, 742 : 50 passengers
742SUD : 120 passengers
743, 744 : 100 passengers
This is due to emergency exit requirements. However, I don't believe that any airline has more than 70 seats upstairs.
Also, those numbers are rough estimates. I don't have my Boeing manuals with me right now.
"The A340-300 may boast a long range, but the A340 is underpowered" -- Robert Milton, CEO - Air Canada