Dash 8-400
Air Traffic Control Developmental
Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
General None Reported / Taken
Human Factors
I was training a developmental on the Departure RADAR position (DR). We had an MD83 cleared for a visual approach to Runway 17R. DHC8 was being vectored to follow the MD83. The MD83 swung out to a very wide base leg which conflicted with the vector the DHC8 was given. The developmental issued traffic to the DHC8 who was leveling at 090 as the MD83 was descending through approximately 085. The DHC8 did report the MD83 in sight and was then cleared to follow the traffic on the visual approach. While all that was happening; PA32 was also being vectored to follow the MD83 and the DHC8. He was assigned heading 120 from the west of the final. While the developmental was trying to sort out the problem between the first two aircraft we allowed the PA32 to come very close to the DHC8. I don't believe their targets merged; but I'm not sure proper traffic was issued. We simply didn't take into account the probability that our MD83 would swing out to such a wide base. I had told the developmental to descend the DHC8; but I hadn't thought to make it clear that I wanted him to keep the DHC8 a thousand feet above the base traffic.
TRACON Controller described a conflict event between an IFR and VFR arrival when an air carrier initiated a wide base turn.