In the prologue to the ST:TNG episode "Conspiracy", Riker gives the order "Increase to warp six", to which LaForge replies "Aye sir, full impulse".
What is going on with these lines of dialog? Was it an attempt to make the Enterprise D seem more advanced in that it could attain significant FTL velocities on impulse engines? Was it a scripting error? Since LaForge's line is delivered off-screen, is it a dubbing error?
Canon (and any attempt to reconcile Star Trek physics with physics as we currently know it) would have impulse drive incapable of attaining light speed, or even a significant fraction of it.
So, was this a deliberate, if misguided, attempt on the part of the show writers to advance Trek canon, or was it a production error?