Interesting that "a spare engine will be mounted on the right wing in the same outer position as the damaged one. But this will only be used to balance the weight during flight and that engine will not be operable." I guess that assumes that the pylon is in a state to hold a whole engine, and that the aircraft can be ferried despite the damage to the wing (or that the damage can be repaired on-site before the ferry). At first sight it seemed odd to bring a whole engine with all its complexity, if they're not going to run it but just use it for balance – anything weighing the same would do. But I suppose an engine is easiest in some ways: it's the right weight and it's designed to be hung on the pylon.