S46 controller reported of a loss of separation due to a particular type of aircraft that climbs out...

Narrative:

Working departure east (a) sector. Gorgeous VMC. The SOP allows sea ATCT to launch successive departures utilizing pilot provided visual separation. The ATCT must modify the secondary scratchpad in the stars data-tag to 'vv' to advise the TRACON that pilot provided visual separation is being used. However; in this case the first aircraft is aircraft X and that type of aircraft is notorious for climbing out much slower than most other aircraft. According to the falcon replay; the trailing aircraft Y is 1.95NM behind aircraft X with approximately a 30 knot overtake. In light of the situation that had already occurred; I stopped aircraft Y at 3000' on the climbout. I do not recall if I restricted his speed; but I believe that I did (230kts). Immediately after observing this situation developing; I flipped on our stop departure lights to terminate automatic releases for sea. I simultaneously made the supervisor aware of the new situation. A final aircraft departed behind aircraft Y. Because aircraft Z was airborne; I decided to turn aircraft Y out to the northwest in an attempt to give myself some room to work. I also restricted aircraft Z to 4000' on initial contact to ensure vertical separation between aircraft Z and aircraft X; in case that became an overtake situation as well. All aircraft subsequently continued their departures without further incident.this is a common problem that we experience at sea with aircraft X [type] departures. I do not know why this specific aircraft type climbs out so differently; but it is common knowledge at the TRACON. I would propose that this situation could be corrected by changing the LOA with sea ATCT to exclude aircraft X [type] departures from the provision allowing the use of pilot provided visual separation between successive departures. If sea ATCT had utilized the standard 3-5nm in-trail spacing that would have been required during IMC; this event would have been completely avoided.

Original NASA ASRS Text

Title: S46 controller reported of a loss of separation due to a particular type of aircraft that climbs out slower than most other aircraft. Controller would like to see LOA changed between Tower and TRACON to exclude this type of aircraft from use of visual separation during climb out.

Narrative: Working Departure East (A) sector. Gorgeous VMC. The SOP allows SEA ATCT to launch successive departures utilizing pilot provided visual separation. The ATCT must modify the secondary scratchpad in the STARS data-tag to 'VV' to advise the TRACON that pilot provided visual separation is being used. However; in this case the first aircraft is Aircraft X and that type of aircraft is notorious for climbing out much slower than most other aircraft. According to the FALCON replay; the trailing Aircraft Y is 1.95NM behind Aircraft X with approximately a 30 knot overtake. In light of the situation that had already occurred; I stopped Aircraft Y at 3000' on the climbout. I do not recall if I restricted his speed; but I believe that I did (230kts). Immediately after observing this situation developing; I flipped on our stop departure lights to terminate automatic releases for SEA. I simultaneously made the supervisor aware of the new situation. A final aircraft departed behind Aircraft Y. Because Aircraft Z was airborne; I decided to turn Aircraft Y out to the northwest in an attempt to give myself some room to work. I also restricted Aircraft Z to 4000' on initial contact to ensure vertical separation between Aircraft Z and Aircraft X; in case that became an overtake situation as well. All aircraft subsequently continued their departures without further incident.This is a common problem that we experience at SEA with Aircraft X [type] departures. I do not know why this specific aircraft type climbs out so differently; but it is common knowledge at the TRACON. I would propose that this situation could be corrected by changing the LOA with SEA ATCT to exclude Aircraft X [type] departures from the provision allowing the use of pilot provided visual separation between successive departures. If SEA ATCT had utilized the standard 3-5NM in-trail spacing that would have been required during IMC; this event would have been completely avoided.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1350297
Time
Date	201604
Local Time Of Day	1201-1800
Place
Locale Reference	S46.TRACON
State Reference	WA
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Large Transport
Operating Under FAR Part	Part 121
Flight Phase	Initial Climb
Flight Plan	IFR
Aircraft 2
Make Model Name	Large Transport
Operating Under FAR Part	Part 121
Flight Phase	Initial Climb
Flight Plan	IFR
Person 1
Function	Departure
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 1.3
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy

S46 controller reported of a loss of separation due to a particular type of aircraft that climbs out slower than most other aircraft. Controller would like to see LOA changed between tower and TRACON to exclude this type of aircraft from use of visual separation during climb out.