mod on the 400 does several things. As stated above, the upper deck is modified aft of the upper deck doors. The floor is removed, thus allowing taller cargo to be loaded aft of the upper deck doors, on the main deck. The cargo handling system is installed on the main deck and the side door is also added. There are other things done, but that's the highlights.
The floor is strengthened in several areas on the main deck, although there are still some weight restricted positions (when compared to the 744F).
The 4056 engines are left and not changed to RR
. This mod would be very expensive as it has not been done before and would have to be certified by the FAA/JAA and other agencies.
The empty weight of the aircraft is generally lighter than a 744F, since there is no nose door and all of the associated equipment for that. The average weight of a 744F is about 159.6 Tonnes and the SF
should be at 157.5 or so.
The stretched upper deck is actually more fuel efficient than the shorter upper deck. The result is the 744F is .85 and the 744(SF) is .86. Not much difference.