ZMP controller observes SF34 initiate evasive TCASII maneuver to avoid radar idented, climbing PA34.

Attributes
ACN	428665
Time
Date	199902
Day	Tue
Local Time Of Day	1201 To 1800
Place
State Reference	SD
Altitude	msl bound lower : 4500 msl bound upper : 7500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zmp.artcc
Operator	common carrier : air carrier
Make Model Name	SF 340B
Operating Under FAR Part	Part 121
Flight Phase	descent : approach descent : holding
Route In Use	arrival : holding pattern
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zmp.artcc
Operator	general aviation : corporate
Make Model Name	PA-34-220T Turbo Seneca III
Operating Under FAR Part	Part 91
Flight Phase	climbout : intermediate altitude
Route In Use	departure : vfr
Flight Plan	VFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar pilot : private
Experience	controller radar : 20 flight time total : 100
ASRS Report	428665
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe inflight encounter : weather other anomaly other
Independent Detector	atc equipment : conflict alert aircraft equipment : tcas other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	faa : investigated
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	Ambiguous
Air Traffic Incident	other

Narrative:

Known cloud layer running from northwest to southeast over the pierre airport, 4600 ft overcast above and to west, clear to the east. Piper seneca departed pierre VFR, requesting IFR. Clearance was denied based on proximity to previous departure and inbound traffic, an SF34. This SF34 was being held at 6000 ft until it had passed the outbound IFR and VFR aircraft. The SF34 advised me that he would like to descend another 200 ft in order to get beneath clouds. I inquired about the cloud cover and issued the VFR traffic. The SF34 advised that he had the traffic on TCASII. I issued a descent clearance to 4500 ft based on this information. It appeared that the aircraft would pass with 1 - 2 mi lateral. I answered other aircraft calls in my sector, and at some point the SF34 advised that they were responding to an RA. I observed both the PA34 and the SF34 climbing, but with very little lateral separation. The SF34 climbed up to +/-7500 ft in response to the PA34 climbing when clear of cloud bank.

Original NASA ASRS Text

Title: ZMP CTLR OBSERVES SF34 INITIATE EVASIVE TCASII MANEUVER TO AVOID RADAR IDENTED, CLBING PA34.

Narrative: KNOWN CLOUD LAYER RUNNING FROM NW TO SE OVER THE PIERRE ARPT, 4600 FT OVCST ABOVE AND TO W, CLR TO THE E. PIPER SENECA DEPARTED PIERRE VFR, REQUESTING IFR. CLRNC WAS DENIED BASED ON PROX TO PREVIOUS DEP AND INBOUND TFC, AN SF34. THIS SF34 WAS BEING HELD AT 6000 FT UNTIL IT HAD PASSED THE OUTBOUND IFR AND VFR ACFT. THE SF34 ADVISED ME THAT HE WOULD LIKE TO DSND ANOTHER 200 FT IN ORDER TO GET BENEATH CLOUDS. I INQUIRED ABOUT THE CLOUD COVER AND ISSUED THE VFR TFC. THE SF34 ADVISED THAT HE HAD THE TFC ON TCASII. I ISSUED A DSCNT CLRNC TO 4500 FT BASED ON THIS INFO. IT APPEARED THAT THE ACFT WOULD PASS WITH 1 - 2 MI LATERAL. I ANSWERED OTHER ACFT CALLS IN MY SECTOR, AND AT SOME POINT THE SF34 ADVISED THAT THEY WERE RESPONDING TO AN RA. I OBSERVED BOTH THE PA34 AND THE SF34 CLBING, BUT WITH VERY LITTLE LATERAL SEPARATION. THE SF34 CLBED UP TO +/-7500 FT IN RESPONSE TO THE PA34 CLBING WHEN CLR OF CLOUD BANK.

Data retrieved from NASA's ASRS site as of July 2007 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.