B757 Undifferentiated or Other Model
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 5
Situational Awareness; Communication Breakdown
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Human Factors
Working final - RWY 35R at Denver. Aircraft X checked in expecting RNAV Zulu RWY 35R Approach. I issued approach clearance and pilot read back correctly. Several miles later I notice that Aircraft X is 2 miles north of the RNAV Zulu path - off course and heading towards the final approach fix. I deem that it is not feasible for the pilot to correct and get back on track - plus - there is another aircraft over the final approach fix and Aircraft X is getting too close to that aircraft. I cancel Aircraft X's clearance and instruct pilot to turn left heading 180. The pilot replies asking what altitude. I descend to 080. At this time there is another aircraft on the final for RWY 35L - Aircraft Y at 090. I heard the final one controller point out the traffic and instruct their aircraft to maintain visual separation. However at the same time I recognize that Aircraft X's turn radius isn't looking good and issue a left turn to heading 150. I pointed out the traffic to Aircraft X as well; but did not instruct Aircraft X to maintain visual separation. B757's seem to always mess up the RNAV Zulu Approaches. My advice would be for the pilots to learn how to maneuver their airplanes properly to avoid pilot deviations that result in errors like this one.
Denver TRACON Controller reported a loss of separation due to an aircraft off course and slow turn radius to get back on course.  The Controller noted that this is a frequent occurrence with B757 aircraft.