Economically, older cargo types can make a lot more sense than a new plane. With the 744 no longer in production, a used model with another 15 years of use at $50mn is a better investment than a new 748 at its $400mn list price. Well-capitalized wet lessors like Atlas can afford to invest in new frames, but if you're a startup or a primarily passenger airline looking to branch out into a few cargo routes, you can't necessarily afford to buy new.
A similar trend occurred with the MD-11. Only a hundred or so frames exist, the last one built in 2000. As a passenger airplane, it was not great: high deck angle in cruise, noise, and of course poor fuel burn compared to projections. But for freight, its nearest competitor is the 77F. A few years ago when I was looking into this, a used MD11 frame would go for around $3mn. With a D-check you could have it flying again for an all-in cost of maybe $10-$15mn and it would last another 10 years. The 77F lists for around $200mn. Thus, even though the M11F is far less efficient than the 77F, it would be 10 or more years before the fuel costs would make up the difference in initial outlay. This is why the MD-11s are still flying.
Passengers prefer new planes, but cargo doesn't complain!
Overnight cargo carriers like FedEx additionally have economics that make this worthwhile. Those planes might typically make only two flights in a day, one to a hub in the evening and one from the hub in the morning.
The efficiency of modern planes is only worth the price if you fly them constantly.
Likewise, this is why there are still freight companies flying (older) aircraft with a three-man crew, including a flight engineer (or four with a loadmaster). Yes, you have to pay an extra crew member… but the initial outlay can be much lower.
My father in law just switched to the triple 7 after a few decades on the MD-11 out of Anchorage. He loved the plane but even with the top spot on seniority the routes kept getting reduced making the 777 more desirable. He often commented that ATC always did a poor job of accounting for their higher approach speed when placing them into the lineup, as they about every other plane out there can fly much slower.
It's interesting - in the current low rates environment, I'd have thought that the initial outlay is much less relevant. On the other hand, even a paltry 2% are $4m a year on a $200m 77F.
Turning this around, though, we should see even more older planes being kept around once rates rise significantly.
A similar trend occurred with the MD-11. Only a hundred or so frames exist, the last one built in 2000. As a passenger airplane, it was not great: high deck angle in cruise, noise, and of course poor fuel burn compared to projections. But for freight, its nearest competitor is the 77F. A few years ago when I was looking into this, a used MD11 frame would go for around $3mn. With a D-check you could have it flying again for an all-in cost of maybe $10-$15mn and it would last another 10 years. The 77F lists for around $200mn. Thus, even though the M11F is far less efficient than the 77F, it would be 10 or more years before the fuel costs would make up the difference in initial outlay. This is why the MD-11s are still flying.
Passengers prefer new planes, but cargo doesn't complain!