SAS and FH, depending on the route from Enterprise to Tullahoma and the speed/altitude profile, gross weight, fuel quantity may well have been a factor. One can stretch out an S-70 ( more than you think, actually ) by getting to 10-12k and flying best range speed, but from the posts here to date, that doesn’t appear to be what was going on.
Another thought occurred: Tullahoma is on a direct route from Ft. Campbell to Atlanta, and there may have been Arista business there, thence proceed to ATL. Just a thought. That would change the thinking re fuel.