In my mind it is related to cost and FedEx is willing to spend the bucks in the prevention of in-flight fires.
Right, Do you know what a STC is and how valuable it is if marketable?
One side of the coin.
Also take in mind what FedEx's insurance cost's are after recent hull losses and the insurance savings they gain by producing and operating with this system...
Guppy, respect you for being a realist on this issue.