Date: 201602
Local time of day: 1801-2400
Location: SEA.Tower, WA
Flight conditions: VMC
Aircraft: Small Aircraft; High Wing; 1 Eng; Fixed Gear
Operator: Air Taxi
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B SEA
ATC / advisory: Tower SEA
Second aircraft: Small Aircraft
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown; Situational Awareness; Training / Qualification
Second reporter function: Local
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Aircraft; Airspace Structure; Procedure; Human Factors
Primary problem: Airspace Structure

Narrative: Aircraft X was on an instrument approach to maintain visual separation with preceding traffic (4.5 miles ahead). The adjacent airport appeared to have quite a bit of VFR traffic during my session on Local Control; so I was scanning that vicinity often. Aircraft X was roughly inside a 3 mile final and had not checked in with tower and I observed Aircraft Y off the adjacent airport turning west (fairly normal procedure).I called TRACON to ask if they could try switching the aircraft to me again. I reached out for Aircraft X again when he was on a 2 mile final and we had stepped on each other. As I unkeyed; that is when I realized that we had stepped on each other; and went right back and issued the traffic that was ahead and to his left; west bound; and altitude indicating 900 feet. Aircraft X was at 1100 feet and descending. By then; the Aircraft Y was passing behind Aircraft X. Another aircraft then checked on that was further out on final. As I was keying up to clear them to land; the other airport tower called to issue a point-out on the aircraft that was traffic for Aircraft X (the aircraft was on a 1.5 mile final by then). No complaints were made that I am aware of.It is my recommendation that the adjacent airport change their departure procedure for their west downwind departure. This departure is commonly used; but does not appear to be adhered to by the pilots nearly as much as it should with our arrivals going right over top of their airport. This departure is known for causing TCAS/RAs for our arrivals and causing go arounds on the regular. While pilots can be tagged for deviations; it would appear that the safest change would be to change the departure.


Second narrative: I was providing On the Job Training (OJT) to my Developmental on Local Control. Two minutes prior to this event; we had a runway incursion where a pilot took another aircraft's take off clearance and entered the runway. There was still discussion going on in the tower about what happened. Aircraft Y called for departure on and requested a [specific Departure procedure]. This was unusual because normally; these Departures are taxied to the opposite runway. The Developmental cleared Aircraft Y for takeoff and approved Departure. I missed that my Developmental said [a departure procedure]; as I was distracted by tower cab discussion of the runway incursion that had just occurred and how to deal with it. Aircraft Y went wide on his crosswind and entered Class B airspace of an adjacent airport under their final. Aircraft X on their final; was in close proximity and the STARS Conflict Alert activated. My Trainee turned Aircraft Y back out of Class B airspace and called the other Tower to point out Aircraft Y and explain the Aircraft Y was getting out of their airspace.End training and get off position whenever an event occurs that will require my explaining what happened to Supervisors. The Developmental may be rattled after the event and need to debrief what happened and collect himself before continuing training. Keep reminding myself to be extra vigilant in watching ALL of my westbound aircraft and help other controllers by watching theirs too.Hold frequent pilot meetings that talk about our airspace; go to flight schools and talk about it. Emphasize Class Bravo; West of the airport and the aircraft on the final; so that the Pilots are more aware of the airspace.


Synopsis: An aircraft departing an airport was issued incorrect VFR departure instructions. The aircraft went into the Class B airspace of the adjacent airport.