Date: 201708
Local time of day: 0601-1200
Location: SEA.Airport, WA
Flight conditions: VMC
Light: Daylight
Aircraft: Medium Large Transport
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Climb
Airspace: Class B SEA
ATC / advisory: Tower SEA
Second aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown; Confusion
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic
Contributing factors: Procedure; Human Factors; Company Policy; Airspace Structure
Primary problem: Procedure

Narrative: I had Aircraft X departing off Runway 16L with a 140 heading issued leaving 1500 feet and Aircraft Y departing off Runway 16C straight out on the SID. Both aircraft were given traffic with intentions on the roll. With both of these aircraft on departure roll; departure keyed in and told me to stop 140 turns. I advised him that I already had one on the roll with the turn issued. He replied leave him straight out. I advised that I was unable because of a jet that was also rolling that would be straight out. He replied that I had to leave the prop straight out. As soon as I could I advised Aircraft X that departure now needed him to fly straight out and issued traffic on Aircraft Y so that I could get pilot visual with these airplanes. At this point Aircraft Y is just off the departure end but below Aircraft X; so Aircraft X was unable to see them. At the point I see Aircraft Y stop his climb to get away from Aircraft X. Departure then keyed in and advised that I could turn Aircraft X to the 140 heading. I issued the turn and shipped Aircraft X to departure. Aircraft Y then advised that he had to respond to a TCAS RA from Aircraft X and had to descend to get away. He continued his climb without further incident. Looking back at the event; I believe that departure shut off the 140 headings reference a jet off that he had already turned and climbed into the area they are supposed to protect for our turns. The departure controllers lack of insight into the effect that they have on our operation put two of my aircraft into unsafe proximity. When I said that I needed the turn he should have come up with another plan or asked if I could provide visual with his jet that was above my prop.Reference the letter of agreement section which states we must turn props that are eastbound to a 140 heading. We don't have guidance for the TRACON turning them off except in the SOP (Standard Operating Procedure). It says we must use the placard. TRACON should never be allowed to use this airspace unless first coordinated and agreed upon by both controllers. Right now they turn them off when needed and often never call to turn them back on until we call and ask if we can use them again. It is my understanding that there is no memory aid for them that reminds them when they are on or off. This is a disservice to the customer as aircraft behind these props are having to wait on the ground longer for us to ensure separation behind these slower aircraft.




Synopsis: SEA Tower Controller reported the TRACON could not accept an aircraft on a previously agreed to heading which placed the aircraft into confliction with parallel runway departure traffic.