Date: 201812
Local time of day: 1801-2400
Location: S56.TRACON, UT
Flight conditions: VMC
Light: Daylight
Aircraft: Embraer Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Climb
Airspace: Class B SLC
ATC / advisory: TRACON S56
Second aircraft: Boeing Company Undifferentiated or Other Model
Reporter organization: Government
Reporter function: Departure
Reporter qualification: Air Traffic Control Developmental
Human factors: Confusion; Workload; Human-Machine Interface; Situational Awareness
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Contributing factors: Airspace Structure; Company Policy; Manuals; Procedure
Primary problem: Procedure

Narrative: I was working the Departure sectors combined allowing the Tower to depart aircraft starting on the same initial departure course with less than minimum separation as long as they ensured pilot-applied visual separation between the aircraft. I was working to get several preceding aircraft above terrain and turned on course in a usual but somewhat complex situation when Tower departed Aircraft X and Aircraft Y with less than 3 miles of lateral separation but with vertical separation. Our departure procedure allows this to occur with pilot-applied visual separation; as long as it is coordinated by including 'VS' on the departure strip. Part of the complexity is that there are up to three different departure controllers scanning strips and they are not always in order of how the check on. Also; departure strips are rarely used; except for checking if a subsequent departure had visual separation. I believe that when the second aircraft departed with less than three miles in trail; I fished through the departure strips to ensure visual separation. I believe I saw a VS on a strip that I thought was Aircraft Y; but apparently I saw the wrong strip; and the two did not have visual separation. I had been working mostly departures all day and the Tower had utilized visual separation all day long; resulting in less than standard separation; without incident; so I was not overly concerned as this happens frequently. My mistake was in not accurately identifying the VS on the correct strip.Assuming that visual separation was applied but wanting to maintain or build separation; I lifted the speed restriction of the first aircraft and the second aircraft was supposed to be maintaining a Tower-assigned 230 knots. Aircraft X took a long time to speed up past his assigned speed and Aircraft Y hit his assigned speed very quickly and began climbing more quickly than Aircraft X. I did not want to assign a much faster speed to the front aircraft because I believed we had visual separation and because I needed him to climb to clear terrain ahead. When preceding traffic was no longer a factor and altitude was sufficient to clear terrain; I turned the Aircraft X to approximately a 030 heading. This instruction was issued and the readback was correct. Aircraft Y remained on a Tower-assigned 340 heading; and climbed to 11;000 feet while the Aircraft X was leaving 11;900 feet about 10 seconds later. Vertical separation was lost prior to the radar indicating that the turn had been made. Once I had standard separation; I turned Aircraft Y to the east behind the Aircraft X and both aircraft continued on their routes without incident or complaint. I was advised the next day that Tower had not applied visual separation between these two aircraft; and that a loss of standard separation was indicated on TARP [Traffic Analysis and Review Program]. The aircraft proceeded on their routes without incident or complaint.TRACON controllers have discussed several times the risks associated with this procedure in two facets. First; the expectation of the pilots to maintain visual separation until routes diverge; sometimes over 20 miles and across several altitude and heading assignments; seems like a misapplication of the rule. I don't think all Tower controllers understand the implications of launching a high-performance aircraft behind a poorly performing aircraft when we in the TRACON cannot turn either for at least 10-15 miles due to high terrain off the east and downwind traffic off the west. We recently had a meeting to discuss procedures that might improve safety and this was submitted in writing by two separate individuals; and verbally at least once; but was disregarded. In fact; some of the staff had chastised the TRACON for not submitting any 'serious' proposals. I and others maintain that this procedure does not meet the intended use of visual separation; that pilots don't understand how long they are supposed to maintain visual; and that it can place aircraft in unsafe situations with few potential resolutions. Also; barring a change to this procedure; I have suggested before that Tower should be required to add 'VS' to the STARS scratchpad for the trailing aircraft when visual separation is applied. Fishing through otherwise unused flight progress strips to find the one that says 'VS' results in several seconds of heads down time; and visual separation is mainly used during busy; complex situations; exactly the situation when you want to be heads-up. Tower already has the option; per the SOP; of adding VS to the scratchpad; but does not utilize it much. I believe it would be a safer operation if the tower were required to add VS to the scratchpad rather than indicate it on a flight progress strip. This would remove the only required usage of flight progress strips for departures and streamline the operation.




Synopsis: S56 TRACON Departure Control trainee reported a loss of separation between two aircraft departing SLC airport.