WAKE TURB IN THE TFC PATTERN.

Narrative

ON INITIAL APCH DSNDING THROUGH 4700 FT; ENCOUNTERED MODERATE WAKE TURB. WE WERE APPROX 7 MI BEHIND TFC. ON FINAL APCH TO LNDG RWY 17R AT DFW AT APPROX 5 MI BEHIND TFC; WE ENCOUNTERED A MODERATE ROLL TO THE L AT APPROX 30 DEGS. WE INQUIRED APCH CTL AS TO WHAT TYPE ACFT WAS IN FRONT OF US; AND THEY SAID IT WAS A COMPANY 757. WE GAVE THEM THE WAKE TURB RPT AND THEY TOLD US WE HAD A 5 MI SEPARATION WITH THE ACFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT THERE WERE ACTUALLY 2 ENCOUNTERS WITH WAKE TURB DURING THIS APCH WITH THE FIRST BEING THE STRONGEST. HE FEELS THAT THIS WAS THE STRONGEST ENCOUNTER IN 15 YRS OF FLT. THE ACFT WAS ON AUTOPLT AT THE ONSET OF THE FIRST ENCOUNTER AND THE AUTOPLT DISCONNECTED AS THE ROLL BEGAN TO INCREASE. HE FELT THAT THE ACFT WAS STILL CTLABLE; HOWEVER. THE RPTR THINKS THAT THE B757 WING CREATES THE STRONGEST WAKE OF THE LARGE NARROW BODIED ACFT AND THAT THE CTLRS ARE NOT VERY CONCERNED. HE WANTS MORE SEPARATION; INCLUDING IF POSSIBLE; EVEN SEPARATE RWYS.