Date: 201910
Local time of day: 1801-2400
Location: PWM.Airport, ME
Flight conditions: Marginal
Light: Daylight
Aircraft: Medium Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class C PWM
ATC / advisory: Tower PWM
Second aircraft: Small Aircraft; Low Wing; 1 Eng; Fixed Gear
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Developmental
Human factors: Training / Qualification; Situational Awareness
Second reporter function: Pilot Flying; Captain
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; 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; Flight Crew Executed Go Around / Missed Approach; Flight Crew Took Evasive Action; General Flight Cancelled / Delayed
Contributing factors: Procedure; Human Factors; Weather
Primary problem: Weather

Narrative: I was working the Local Control position at the time of the event. Aircraft Y had just departed for left closed traffic. Aircraft X was on final. We were advertising 1;200 ft. ceilings at the time. Aircraft Y was midfield when he advised that he wanted a stop and go. I told him that if he wanted a touch and go that he could be number one. Aircraft Y didn't respond so I told him to extend his downwind and that I would call traffic for him to follow as he got closer. He didn't respond again so I repeated for him to extend his downwind to which he complied. As I looked up at the radar after scanning the runway; I noticed that Aircraft Y was tracking close to the final with Aircraft X closing in. I instructed him to make a right 360 degree turn to get him more comfortably out of the way for the inbound Aircraft X. At this point I saw Aircraft Y start his turn and I had Tower apply visual separation between Aircraft Y and Aircraft X. Aircraft X asked if there was traffic ahead of him and I told him it was ahead and to his left; 1;000 ft. northbound. Aircraft X responded; 'Roger; we're getting a TCAS RA (Resolution Advisory) and we're climbing.' I said roger; then came back with fly runway heading and maintain 3;000 ft. to which Aircraft X complied. Aircraft X was vectored around by Approach for a safe landing; and Aircraft Y did a lap in the local traffic pattern and landed safely as well. Make sure to let everyone know about everyone in a more timely manner; and insure that with weather moving in that ATC instructions are more promptly followed by aircraft.


Second narrative: I had to respond to an RA (Resolution Advisory) due to loss of aircraft separation between my flight; Aircraft X; and Aircraft Y. Weather conditions at the time of the event had the ceilings around 1;000 ft. We were vectored onto the ILS 1;800 ft.; cleared for the approach and handed over to Tower. We contacted Tower and were cleared to land. Listening to the live ATC archive - Tower had instructed Aircraft Y that he would need to extend his downwind leg due to arriving traffic. The Aircraft Y pilot impatiently replied ok. The problem is that it appears that this impatient pilot decided to turn base without permission from ATC or alerting anyone of his actions. This placed him directly in our flight path resulting in the loss of separation. As we were descending on the glide slope we heard Tower call Aircraft Y and ask them for a 360 degree turn. It was at this point that we noticed them on our TCAS system as a target and we received the RA 'Climb.' We were at approximately 1;200 to 1;300 ft. and we were IMC. I responded accordingly. We were IMC for the entire event. There is no doubt in my mind that this pilot was busting VFR cloud separation requirements for Class C airspace. Multiple aircraft report the bases as 1;000 ft. Another pilot shortly after our event queried the Tower as to how Aircraft Y can be on a downwind in this weather. Tower stated that the ceiling is at 1;200 ft. and that he is at 1;000 ft. The same pilot that asked this question reported the bases as 1;000 ft.; [and] Aircraft Y followed him to the airport. This is a reminder as to why VFR cloud separation requirements are in place. What greatly concerns me about this event is that this incident was preventable. It is clear the Aircraft Y pilot was busting cloud separation requirements and violating ATC instructions. In summary there are two items that led to loss of aircraft separation. The pilot of Aircraft Y violated VFR cloud separation requirements for Class C airspace while doing pattern work. The Aircraft Y pilot decided to turn base without permission from ATC or alerting anyone of his actions. This placed him directly in our flight path resulting in the loss of separation.


Synopsis: PWM Tower Controller and Air Carrier Captain reported an aircraft in the VFR pattern not complying with ATC instructions and conflicting with traffic; resulting in a TCAS RA.