Avl controller described near loss of separation involving two overflight aircraft; descending both ...

Narrative:

Aircraft #1 assigned 9;000 ft; was southbound destined gmu overflight through my airspace. Aircraft #1 was cruising at approximately 130 KTS. Aircraft #2 assigned 10;000 ft; was south-southeastbound to gsp. Aircraft #2 was cruising at approximately 160 KTS. Aircraft #2 at 10;000 ft was 1 mile north of aircraft #1 at 9;000 ft. Per LOA with gsp approach; all aircraft destined gmu and gsp are to receive 7;000 ft before transfer of control. At this time aircraft #1 was instructed to descend and maintain 7;000 ft. 30 seconds later; aircraft #2 was 1 mile south of aircraft #1 and was then instructed to descend and maintain 7;000 ft; all the while pulling away laterally from aircraft #1 due to aircraft #2's higher airspeed. At 2.5 miles lateral separation; the 2 aircraft were 800 ft vertically separated. Aircraft #2 was descending much quicker than aircraft #1. At one point; aircraft #1 was at 8;400 ft while aircraft #2 was at 9;200 ft and less than 3 miles. 15 degrees of divergence was not guaranteed since I never asked or assigned a specific heading. When I noticed that potential separation was lost; I issued traffic to aircraft #1 to which he replied 'no joy' on the traffic (aircraft 2). Then I immediately amended aircraft #2's altitude and told him to maintain 9;000 ft. Gmu and gsp are approximately 10-12 NM apart east and west from each other. Both gsp and gmu are 10 NM south of the southern portion of avl's radar airspace boundary. The loss of separation (if it is deemed a loss of separation) took place approximately 3 miles south of avl. The TRACON position; or radar room position; was combined in the tower. I was working radar traffic on a d-brite. I had worked 2 hours on local control and had a 1/2 hour break before returning back to the radar position.

Original NASA ASRS Text

Title: AVL Controller described near loss of separation involving two overflight aircraft; descending both during an overtake situation; Controller corrective action saved separation.

Narrative: Aircraft #1 assigned 9;000 FT; was southbound destined GMU overflight through my airspace. Aircraft #1 was cruising at approximately 130 KTS. Aircraft #2 assigned 10;000 FT; was south-southeastbound to GSP. Aircraft #2 was cruising at approximately 160 KTS. Aircraft #2 at 10;000 FT was 1 mile north of Aircraft #1 at 9;000 FT. Per LOA with GSP Approach; all aircraft destined GMU and GSP are to receive 7;000 FT before transfer of control. At this time Aircraft #1 was instructed to descend and maintain 7;000 FT. 30 seconds later; Aircraft #2 was 1 mile south of Aircraft #1 and was then instructed to descend and maintain 7;000 FT; all the while pulling away laterally from Aircraft #1 due to Aircraft #2's higher airspeed. At 2.5 miles lateral separation; the 2 aircraft were 800 FT vertically separated. Aircraft #2 was descending much quicker than Aircraft #1. At one point; Aircraft #1 was at 8;400 FT while Aircraft #2 was at 9;200 FT and less than 3 miles. 15 degrees of divergence was not guaranteed since I never asked or assigned a specific heading. When I noticed that potential separation was lost; I issued traffic to Aircraft #1 to which he replied 'No joy' on the traffic (Aircraft 2). Then I immediately amended Aircraft #2's altitude and told him to maintain 9;000 FT. GMU and GSP are approximately 10-12 NM apart east and west from each other. Both GSP and GMU are 10 NM south of the southern portion of AVL's radar airspace boundary. The loss of separation (if it is deemed a loss of separation) took place approximately 3 miles south of AVL. The TRACON position; or radar room position; was combined in the Tower. I was working radar traffic on a D-BRITE. I had worked 2 hours on local control and had a 1/2 hour break before returning back to the radar position.

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	831265
Time
Date	200904
Local Time Of Day	0601-1200
Place
Locale Reference	AVL.Airport
State Reference	NC
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	Initial Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	Bonanza 35
Operating Under FAR Part	Part 91
Flight Phase	Initial Approach
Flight Plan	IFR
Person 1
Function	Approach
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Radar 0.3 Air Traffic Control Time Certified In Pos 1 (yrs) 0.3
Events
Anomaly	Conflict Airborne Conflict
Miss Distance	Horizontal 13200 Vertical 800

Avl controller described near loss of separation involving two overflight aircraft; descending both during an overtake situation; controller corrective action saved separation.