S56 controller reports of a near midair collision caused by an un-anticipated climb rate of one airc...

Narrative:

While working approach for the satellite airports; aircraft X had been released IFR with the previous controller. Several flights of fighters were inbound for their recoveries back to hif. I misjudged the climb rate characteristics for aircraft X and had anticipated them to climb at a faster rate than they did. They were assigned a vector to join the airway; climbing. Traffic was issued to aircraft Y; 4/fighters several times and also to aircraft X. The conflict alert did not go off. When the fighters were 4NM west; I answered another flight checking in instead of issuing a traffic alert. I felt the projected flight path of the fighters was behind that of aircraft X. However; after reviewing the tape I recognized that I did not see the wingman's primary target pass directly below aircraft X. At the crossing point; aircraft X was at 8100 feet and aircraft Y flight indicated 7600 feet. I do not know what altitude the wingman who passed below aircraft X was. The pilot of that aircraft called to report a near midair collision. Consider aircraft characteristics more appropriately. Maintain a more diligent scan.

Original NASA ASRS Text

Title: S56 controller reports of a NMAC caused by an un-anticipated climb rate of one aircraft and the possible altitude deviation of a flight of four aircraft.

Narrative: While working approach for the satellite airports; Aircraft X had been released IFR with the previous controller. Several flights of fighters were inbound for their recoveries back to HIF. I misjudged the climb rate characteristics for Aircraft X and had anticipated them to climb at a faster rate than they did. They were assigned a vector to join the airway; climbing. Traffic was issued to Aircraft Y; 4/fighters several times and also to Aircraft X. The conflict alert did not go off. When the fighters were 4NM west; I answered another flight checking in instead of issuing a traffic alert. I felt the projected flight path of the fighters was behind that of Aircraft X. However; after reviewing the tape I recognized that I did not see the wingman's primary target pass directly below Aircraft X. At the crossing point; Aircraft X was at 8100 feet and Aircraft Y flight indicated 7600 feet. I do not know what altitude the wingman who passed below Aircraft X was. The pilot of that aircraft called to report a NMAC. Consider aircraft characteristics more appropriately. Maintain a more diligent scan.

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	1224766
Time
Date	201412
Local Time Of Day	1801-2400
Place
Locale Reference	S56.TRACON
State Reference	UT
Environment
Light	Night
Aircraft 1
Make Model Name	Helicopter
Flight Phase	Cruise Climb
Flight Plan	VFR
Aircraft 2
Make Model Name	Fighter
Operating Under FAR Part	Part 91
Flight Phase	Cruise Initial Climb
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Approach
Qualification	Air Traffic Control Developmental
Events
Anomaly	ATC Issue All Types Conflict NMAC

S56 controller reports of a near midair collision caused by an un-anticipated climb rate of one aircraft and the possible altitude deviation of a flight of four aircraft.