Navigational failure leads to a four year drift. I just don't see the problem. I actually like that it bothers to give us a time differential, because Alien 3 doesn't bother to indicate how much time has supposedly passed. Evidently it was supposed to be immediately following on from Aliens, but it would have been nice to have established that, especially since the Sulaco somehow drifted into close proximity of Fury 161.
Ripley's shuttle drifted for 57 years before finally being picked up, and that was with an in-film establishment of what the average turn around time was on the missions, counted in weeks and months, not years.
