Date: 201407
Local time of day: 0601-1200
Location: DFW.Airport, TX
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: PC-12
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B DFW
ATC / advisory: TRACON D10; Tower DFW
Aircraft component: FMS/FMC
Component problem: Design
Reporter organization: Personal
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Human-Machine Interface; Distraction; Confusion; Time Pressure; Workload
Second reporter function: First Officer; Pilot Flying
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic; Flight Crew FLC Overrode Automation
Contributing factors: Airport; Human Factors; Procedure
Primary problem: Human Factors

Narrative: Approaching DFW from the northwest via the BOWIE2 STAR we were proceeding direct to ICKEL at 5;000 feet for an expected ILS approach to RWY 18R. Approximately 8 miles from ICKEL; ATC advised us to expect Runway 17L; maintain 5;000 feet and current heading. We deselected Nav on the autopilot and selected heading mode and immediately started the procedure of changing the FMS programmed approach from 18R to 17L. ATC issued a frequency change; we checked in on the new frequency at 5;000 feet with assigned heading. The new Controller acknowledged our check-in and advised to expect Runway 17L. We were then cleared to 4;000 feet which was acknowledged. ALT hold was deselected and a descent initiated. The 17L approach had not yet been successfully loaded; but the Controller gave us the LOC frequency which was dialed into the #1 Nav. The Controller directed us to start the descent as it looked to her that we had actually climbed. The descent rate on the autopilot was increased and the FMS finally accepted and displayed the ILS 17L approach. The Controller cleared us to intercept the localizer and to expedite the descent to 3;000 feet. Being too close to the localizer to try and select an FMS commanded intercept; and seeing that we were probably going to overshoot the 17L localizer; the autopilot was disconnected; the rate of descent was increased and a right turn to intercept the localizer was initiated. After rolling out 1 dot right of the localizer an immediate corrective left turn was started. The Controller advised that it looked like we had lined up on 17C and asked if the airport was in sight then rapidly issued vectors of 150 degrees followed by 140; and then 120; all of which were complied with. The airport in sight call was made as we rolled back right to track the localizer; intercepted the glideslope and handed over to DFW Tower. Tower check-in and landing clearance were followed by an uneventful landing. At some point just prior to the Tower handoff; the Controller called traffic at 3 o'clock high which was acknowledged with 'traffic in sight.' The traffic was an airliner whose pilot stated he was too high to make the landing and requested vectors for another approach. The Controller apologized to him and said that she had had a Pilatus pilot ahead of him who appeared to be confused.This flight culminated with the one thing I dread when approaching a busy Class B airport; a close in to the airport runway change. The FMS; which had been programmed with the initial expected runway approach well before entering the congested terminal area; must be reprogrammed. New altitudes must be reviewed; new frequencies entered; and checklists completed all while funneling toward ever more congested airspace and frequencies. Even multi-crew aircraft often find their plate full when this happens. When we felt that the autopilot was not responding crisply enough to the changes it was given; we turned it off and hand flew the course intercept and approach. I fly into DFW frequently and have had no problems except when given a close-in runway change. The problem was compounded [in this case] by our desire to maintain a higher airspeed than normal so faster traffic behind wouldn't be inconvenienced. In the future; I will fly normal approach speeds.The runway change given by ATC created higher than needed workloads and [greater] conflict potential for all involved. Such changes should be questioned earlier and amended or avoided altogether. An earlier call of 'runway in sight' and use of a visual approach clearance would have made things easier for all of us; and might have saved the airliner's approach. Sometimes controllers are too controlling and pilots do not often enough take advantage of PIC [requested options] for visuals; etc. weather permitting. During the dreaded phone call after the flight; the TRACON Supervisor said he was looking into a possible pilot violation due to a Loss of SeparationAlarm.


Second narrative: [Report narrative contained no additional information].


Synopsis: The time needed to locate; select; program; assess; assimilate and brief a late runway change--from 18R to 17L--as they descended into DFW contributed to the decision by the flight crew of a PC-12 to deselect the autopilot believing they were too close for an automated intercept.  The manually flown intercept was too aggressive and a loss of separation with another aircraft ensued.