Narrative:

Working departure sector. Gorgeous VMC. The SOP allows tower to launch successive departures utilizing pilot provided visual separation. The tower 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 an A321 and that type of aircraft is notorious for climbing out much slower than most other aircraft.according to the falcon replay; the trailing B737-800 is 1.55 miles behind the A321 with a 60 knot overtake. I restricted the B737-800 to 230 knots and requested the A321 increase to 250 knots as soon as possible. Despite those efforts the situation continued to compress. While I was aware pilot provided visual separation was being utilized; in my judgment the situation had become unsafe and I decided to break our noise abatement procedures and initiate an early eastbound turn for the B737-800. After initiating the turn I made the supervisor aware of the situation. Both aircraft subsequently continued their departures without further incident.this is a common problem that we experience with the A321 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 letter of agreement to exclude A321 departures from the provision allowing the use of pilot provided visual separation between successive departures. If tower had utilized the standard 3 to 5 mile in-trail spacing that would have been required during IMC; this event would have been completely avoided.

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Original NASA ASRS Text

Title: A procedure allowing pilot provided visual separation between successive departures caused a conflict between an A321 aircraft climbing at a much slower airspeed than a B737-800 departing behind the A321.

Narrative: Working Departure sector. Gorgeous VMC. The SOP allows Tower to launch successive departures utilizing pilot provided visual separation. The Tower 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 an A321 and that type of aircraft is notorious for climbing out much slower than most other aircraft.According to the FALCON replay; the trailing B737-800 is 1.55 miles behind the A321 with a 60 knot overtake. I restricted the B737-800 to 230 knots and requested the A321 increase to 250 knots as soon as possible. Despite those efforts the situation continued to compress. While I was aware pilot provided visual separation was being utilized; in my judgment the situation had become unsafe and I decided to break our noise abatement procedures and initiate an early eastbound turn for the B737-800. After initiating the turn I made the supervisor aware of the situation. Both aircraft subsequently continued their departures without further incident.This is a common problem that we experience with the A321 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 Letter of Agreement to exclude A321 departures from the provision allowing the use of pilot provided visual separation between successive departures. If Tower had utilized the standard 3 to 5 mile 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.