ARTCC controller hands off two aircraft to terminal facility; with compression leading to minimum se...

Narrative:

Aircraft X was descending to the bottom of my airspace and assigned 280 knots. Aircraft X was under nct approach's control. Aircraft Y was about 7 miles behind aircraft X; descending to FL240 and reducing speed to 260 knots; but still faster by about 30 knots over the ground than aircraft X. Nct called for control of aircraft X when aircraft Y was at about FL270. I shipped aircraft Y to nct with still about 7 miles lateral; 1500 feet vertical and 20 knots faster over the ground and slowing. It appeared to me that aircraft X was slowed by nct as his ground speed fell by about 40 knots; and at the same time slowed his descent and eventually leveled at FL240. Aircraft Y continued his descent while on nct's frequency to aircraft X's altitude and continued to have an overtake as aircraft X had by now slowed considerably over the ground; even as aircraft Y was also slowing. Nct eventually turned aircraft Y with about 5 miles lateral separation. Approach control separation was never lost; and they were talking to both aircraft; but it was close for a center controller. My expectation was that nct was either going to keep aircraft X descending and going fast; or turn aircraft Y earlier. As it was; it was a non-issue; but coordination could have been clearer between us. I could have asked nct if they wanted anything else done before I shipped the following aircraft; or they could have let me know what they had planned.

Original NASA ASRS Text

Title: ARTCC Controller hands off two aircraft to terminal facility; with compression leading to minimum separation and corrective turn by the terminal facility.

Narrative: Aircraft X was descending to the bottom of my airspace and assigned 280 knots. Aircraft X was under NCT Approach's control. Aircraft Y was about 7 miles behind Aircraft X; descending to FL240 and reducing speed to 260 knots; but still faster by about 30 knots over the ground than Aircraft X. NCT called for control of Aircraft X when Aircraft Y was at about FL270. I shipped Aircraft Y to NCT with still about 7 miles lateral; 1500 feet vertical and 20 knots faster over the ground and slowing. It appeared to me that Aircraft X was slowed by NCT as his ground speed fell by about 40 knots; and at the same time slowed his descent and eventually leveled at FL240. Aircraft Y continued his descent while on NCT's frequency to Aircraft X's altitude and continued to have an overtake as Aircraft X had by now slowed considerably over the ground; even as Aircraft Y was also slowing. NCT eventually turned Aircraft Y with about 5 miles lateral separation. Approach control separation was never lost; and they were talking to both aircraft; but it was close for a Center Controller. My expectation was that NCT was either going to keep Aircraft X descending and going fast; or turn Aircraft Y earlier. As it was; it was a non-issue; but coordination could have been clearer between us. I could have asked NCT if they wanted anything else done before I shipped the following aircraft; or they could have let me know what they had planned.

Data retrieved from NASA's ASRS site as of April 2012 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	864617
Time
Date	200912
Local Time Of Day	1801-2400
Place
Locale Reference	ZOA.ARTCC
State Reference	CA
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Aircraft 2
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Procedural Published Material / Policy

ARTCC controller hands off two aircraft to terminal facility; with compression leading to minimum separation and corrective turn by the terminal facility.