Even more capable is the final variant of the venerable 747 program, the
747-8F, which could carry a substantially larger payload of 314,500
pounds to the target altitude. The problem with planning the fleet based
on this super-jumbo is that the last 747-8 was delivered in January 2023
and the production line has closed39. Consequently,
obtaining new aircraft from Boeing would require a line restart roughly
a decade from now, and the chances of that are remote. Just 107 747-8Fs
were delivered, along with 48 in passenger
configuration40. The polar SAI mission would require
more than 70 such aircraft, which is to say most of the production
freighter fleet and roughly half the total fleet. The likelihood that so
large a proportion of the delivered fleet could be acquired on the
secondhand market is low, and passenger aircraft converted to the tanker
mission would have marginally reduced payloads relative to the
production freighters. Nonetheless, some substantial proportion of a
polar SAI fleet perhaps could be assembled via used 747-8s. This raises
the prospect of a mixed SAI fleet, consisting of some repurposed 747-8s
and perhaps some similarly repurposed mid-life 777s, operating alongside
a core of factory- delivered 777 Special Tankers. Freight operators are
opportunistic in their fleet acquisitions and therefore customarily have
a mix of production freighters and repurposed second-hand aircraft in
their fleets. An SAI fleet might be similarly composed. Nonetheless, for
the purpose of the discussion hereafter, we will assume an all 777
Special Tanker fleet is newly acquired from Boeing, noting that in fact
some portion of it might be otherwise acquired.