You can say it as many times as you want. It won't make it right. Your analysis is for a 10-15 year airline. You can't simply compare the total costs of a new airplane that lasts 25 years versus the total costs of used model that only lasts 12. You need to push the used costs out to 25 as well, unless you plan to permanently remove that capacity from your airline in 12.

Let's go a step farther to look at the new order part. We know what

DL has on order, and it's not enough to replace their fleet, let alone grow it. We can roughly evaluate where

DL is at in regards to their widebody fleet. All of their planes have ages and approximate life spans. Let's go back about a year, before the 747 retirements and A330 deliveries, and for simplicity leave the international 757s out of this.

DL had 145 widebody international airplanes with X amount of capacity. Assume new widebodies to last an average of 25 years or roughly 100,000-120,000 hours.

DL had only 42 widebodies under the halfway mark in age, with none less than 4.5 years old. Assuming equal capacity for each aircraft and flat company capacity, the rough average is that

DL will need to buy 5.8 new widebodies a year to maintain their fleet.

DL had 60 new aircraft on order a year ago (I'm not counting the 787s since that order will be changed, if it happens at all) with a higher total capacity than the current aircraft they will replace. Those two orders will more than cover the 5.8 per year for when the last A339 will be delivered. If we assume the last delivery is 2022, that's 60/8 years=7.5 per year. But as we can see,

DL has kicked the can down the road too many times already. They need to acquire many more airplanes than the average in the next 10-15 years if they expect to just maintain their airline, let alone grow it. And that's where the new/used debate comes in. If

DL wants to shut down in 10-15 years, a used airplane is relatively very compelling. If

DL wants to be a top airline 15 years from now, as they are today, used has a harder time winning the comparison.

[Edited 2015-10-16 13:13:16]