[rogerbinns]

The dedicated cargo freighter market has been in decline for quite a while, but the volume of cargo has been increasing. The reason is cargo goes in the holds of passenger aircraft. This is nice extra money for the airline: the plane was going to go anyway, the crew is paid for, the fuel difference is minimal etc.

Remember that planes are already double decker (triple for A380). They look like this: https://qph.ec.quoracdn.net/main-qimg-4c732e2865f73d86b72c5a...

The bottom deck has fuel tanks, passenger bags, and space for cargo. The A380 (passenger version) is problematic for cargo because there are two passenger decks which means up to twice the lower deck taken up with baggage leaving less for the cargo.