FTW85IA149

Drg arr, a Beech A36, N2057A, was vectored for an ILS rwy 17L apch while a hvy Boeing 747 was being vectored for an ILS rwy 18R apch. The ATC arrival controller (ctlr) stated he had 'staggered' the A36 bhnd the 747 with at least 3 mi sepn. After the A36 was inbnd on the ILS localizer (LOC), it encountered wake turbc from the 747, but the plt recovered & lnddsafely. Inv revealed that as the 747 was apchg the ILS 18R LOC fm the west, its crew was told to make a 'hard rgt turn' to join the LOC. Drg the turn, the 747 dscndd fm 5700' to 4100', then contd dscndg to 3000' while inbnd on the apch. Radar data showed that the ctlr had delayed the 747'S vector to the 18R LOC & that the 747 overshot its LOC & converged to within 600' of the 17L LOC. As the A36 turned to intercept the 17L LOC, it had an interval of aprx 90 sec behind the 747. There was evidence that the wing tip vortices fm the 747 had settled at a rate of 400 to 600 ft/min & drifted twd the A36'S flt path. Procedures reqd 5 mi sepn when a small acft was flwg directly bhnd & within 1000' blo a hvy jet.