this weeks "Flight" article on the 747 notes there are 234 747 freighters in service - of these 217 are -400 models with an average age of 16 years - but the oldest is a 200F with 38 years on the clock
"although certain operators love the nose door capability of the 747, the -8F is a large aircraft to fill and more cargo users are favouring the 777F. Plus low oil prices extend the life of current -400F's..."
Their Ascend forecast in 2015 was only another 57 -8's to be built but even that is now looking optomistic.........................
"a rate of 0.5 a month is not sustainable in the long, or even medium, term"