It APPARENTLY is true on the RB-211-535 series when thrust is reduced to flight idle at crz altitudes..the epr (measured across the fan only on the e-4 engines) shows less than "1.00" which would indicate that the fan is simply windmilling..however there is still a small amount of tailpipe thrust being produced...so negative thrust doubt it..coldstream fan negative thrust/windmilling drag perhaps...comments anyone?