With the advent of the 61/63 series,Douglas introduced a limit of the amount of 'reverse'one could select in the Air(legal).Up until this time one could select ,if required,MCT on all four for the descent..With the stronger engines,and after certain 'freighter'operations(Used to cruise to 60miles of destination-then use all in MCT),which twisted the pylons-Douglas limited the inboards only to MCT,and 250knots??
I believe that the CFM required a New Pylon design
