Flight Crew Commercial; Flight Crew Instrument; Flight Crew Multiengine; Other SEA
Flight Crew Last 90 Days 30; Flight Crew Total 8300; Flight Crew Type 3500
Situational Awareness; Distraction; Communication Breakdown
ATC Issue All Types; Conflict NMAC; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Separated Traffic; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action
Airspace Structure; Procedure; Human Factors
Initially reported to Tower my position and I was cleared to enter the right downwind. Adjacent to the Class D boundary common with the Class D airspace boundary with the adjacent airport; I was given a traffic advisory of a small aircraft inbound. I had that aircraft in sight and reported so. I was then instructed to 'Turn left and follow that traffic' I refused the left turn as that would have taken me into the adjacent airport Class D; so reported 'negative left turn; I am turning right and following the [small aircraft]'. When approaching there were three planes on the right downwind for the runway. Aircraft Y who was cleared to land short approach with a long landing; the small aircraft I was following and myself who was cleared to land number 3.Shortly after that; something caught my eye in my right peripheral vision. As I scanned it was an airplane broadside to me; northerly heading; at the same altitude as me; in a slight climb. As a collision was extremely possible; I took evasive action by chopping power and nosed over going negative G to miss the aircraft. I contacted the Tower of who was that airplane and why was he in my vicinity and not called for traffic. Controller went into meltdown about who was who and who was where. By this time the small aircraft I was following had landed. I did not follow the previously issued landing clearance to land number 3 behind the small aircraft; but rather followed this mystery plane which was finally identified as an X type plane who had been in the left closed traffic pattern doing touch and goes. Apparently; this plane made a right pattern after takeoff and went right into me on the right downwind. Controller and any supervisors should be watching that aircraft comply with the proper traffic patterns; and if there is a deviation; notify other aircraft that such non-compliance could create a traffic conflict.
Due to a staffing shortage; the other two controllers in the cab were both Supervisors; which one was on Operational Supervisor and the other on Ground Control. [This was] an abnormal configuration at this time of day. Aircraft Y had been in the pattern with minimal traffic before I took the local position. Aircraft A reported inbound from the northwest. Aircraft A seemed unfamiliar and I provided him extra assistance. When Aircraft X checked on; inbound from the northwest; I had him follow Aircraft A as I preferred not to give Aircraft A more instructions than I deemed he could handle. Aircraft Z checked on inbound from the south. TRACON called with a direct for Aircraft B. I instructed Aircraft Y to extend climb straight out to a point and make right traffic to avoid Aircraft B's expected left downwind entry at a high rate of speed.The Supervisor stated that Aircraft C was inbound from the east for a hospital. I asked if Aircraft C was coordinated by TRACON or did I miss the check in. The Supervisor said TRACON had coordinated it. The Supervisor and Ground Control continued to debate with each other the intention of Aircraft C; the background noise can be heard in the background. Traffic on final needed to extend downwind; and thus; created a problem with Aircraft C's trajectory to cross the runway final. I asked the Supervisor to find out Aircraft C's intentions. Aircraft X reported a near mid-air collision with a small aircraft which was not the correct aircraft. This prompted me to verify Aircraft Z's position. Aircraft Z confirmed his position. Aircraft X mistook Aircraft Y; as Aircraft Z. It was at this time that I realized Aircraft Y had turned in front of Aircraft X. I allowed my attention to be drawn away from my pattern. I appreciate other controllers/ supervisors willing to provide assistance; but because all the information was not known it added another distraction to the operation.Aircraft C ended up entering the airspace without coordination. Aircraft C contacted MRI as he exited MRI airspace. Do not expect aircraft to fly the left and right downwind the same. Extend aircraft further if necessary. Tell aircraft to extend further out even if it extends the pattern. Do not allow others in the cab to distract you. Other controllers and supervisors' assistance is needed in the cab and appreciated. If; however; you do not have all the known information; before distracting the local controller; confirm with the appropriate facility/ sector the intentions of all aircraft.
A Tower Local Controller and pilot in the pattern reported a NMAC when one of the aircraft turned in front of an aircraft the Local Controller intended for it to follow. The Tower Controller reported as this was occurring another aircraft entered the airspace without the proper coordination.