Don't forget engine maintaince costs, which is not small change, two engines means half the cost.

p.s. Reliability is another factor, if the 747's 4 have the same reliability as the 777's 2, then the 747 is twice as likely to break down.

a downside for twins, however, is if one engine breaks down it's gotta be fixed on the spot. A four engined plane can be ferried without passengers to another location for repairs.

[This message has been edited by snake (edited 02-23-2003).]