Date: 201509
Local time of day: 1201-1800
Location: A80.TRACON, GA
Flight conditions: IMC
Light: Daylight
Aircraft: Large Transport
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class B ATL
ATC / advisory: TRACON A80
Second aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Reporter organization: Government
Reporter function: Approach
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown; Situational Awareness; Training / Qualification
Second reporter function: First Officer
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Contributing factors: Procedure; Airspace Structure; Human Factors
Primary problem: Procedure

Narrative: Training in progress on final A; east operation with triple ILS Precision Runway Monitoring (PRM) approaches in IFR weather.[AIRCRAFT X] was on the downwind descending to 3;000 feet. [AIRCRAFT Y] was on the base leg northbound descending to 3;000 feet. We turned [AIRCRAFT X] northbound on a right base. Once [AIRCRAFT X] began the turn; we turned [AIRCRAFT Y] to a 030 degree heading to achieve desired spacing behind [AIRCRAFT X]. [AIRCRAFT X] appeared to roll out on a 300 degree heading instead of a 360 degree heading. The trainee then turned [AIRCRAFT Y] left to a heading of 360; and then turned him left again to a heading of 330. [AIRCRAFT X] continued on what appeared to be a 300 degree heading. I then took the frequency and turned [AIRCRAFT X] all the way right to a 080 heading to join the final. Separation was lost and decreased to 2 miles with no vertical. Once the aircraft were separated again I turned [AIRCRAFT Y] east to join the final 4 miles behind [AIRCRAFT X]. Visual separation was not attempted during this incident because the aircraft were in IMC conditions the entire time.The very nature of working finals dictates that aircraft are on converging downwind and base headings. The volume of traffic here assures that aircraft will be in proximity to other aircraft; and prompt compliance with ATC instructions is of paramount importance to ensure passenger and crew safety. There is no place for a turn in the final box that is off by 60 degrees.We could have slowed [AIRCRAFT X] prior to a northbound turn instead of combining the two instructions. The spacing between aircraft in this scenario made that unnecessary; and I feel that I made every effort to put these two aircraft on the final safely and efficiently while conducting On the Job Training (OJT). The trainee action in the scenario was not incorrect in my opinion. I depend on the aircrew for prompt compliance; and expect them to perform the instructions that I assign and they read back. That did not happen here. I cannot speculate as to why; as I am not qualified and current in [that type of aircraft].To prevent re-occurrence of this event; I recommend the aircrew does what they are instructed to do when they are instructed to do it.


Second narrative: We were arriving on the Arrival for the ILS approach. We'd been given a descent to 3;000 feet. ATC gave us a vector to heading 360 which took us off the arrival for approach vectors. The Captain input 360 heading into the Heading Selector and the aircraft commenced a 30 degree banked turn to the assigned heading. I saw an aircraft on TCAS at our altitude and started scanning outside for it (never saw it due to clouds and reduced visibility). Shortly thereafter; we were given a 080 heading to join the Localizer; with instructions to make a 'quick turn on around' or some similar verbiage. I thought this a bit unusual; but we continued our turn and intercepted the Localizer and conducted a normal IFR Approach and landing. At no time did we appear to cross through the Localizer or roll wings level during the turn. The approach was stable and everything seemed normal. After landing and taxiing into the ramp; we were given a phone number to call. I called; and the Approach Controller said it appeared that we had maintained a heading of 300 degrees or 320 degrees for approximately four miles during the turn to 360 degrees from the downwind; causing a loss of separation (2.6 miles I think) with another carrier aircraft. At no time did we get a TA or RA; or alert from ATC. I'm not sure what caused the incident; as to the best of my knowledge we followed ATC's instructions completely. If the heading was changed while I was scanning outside; I did not catch it; but I never saw or felt the aircraft roll wings level during the turn. The turn from base to final seemed to come a bit late.


Synopsis: Controller Training in progress. Trainee gave radar vectors for sequencing and separation to the final approach course. Aircraft turned at a much slower rate than Controllers anticipated. Instructor took over sector and issued vectors to both aircraft but it was too late to maintain required separation standards. Pilots also reported and did not realize that the loss of separation had occurred.