Air carrier has near midair collision with small aircraft on approach into tys.

Attributes
ACN	264177
Time
Date	199401
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : tys
State Reference	TN
Altitude	msl bound lower : 2500 msl bound upper : 3500
Environment
Flight Conditions	IMC
Light	Dusk
Aircraft 1
Controlling Facilities	tracon : tys
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent : approach descent other
Flight Plan	IFR
Aircraft 2
Make Model Name	PA-38 Tomahawk
Operating Under FAR Part	Part 91
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : commercial pilot : flight engineer
Experience	flight time last 90 days : 120 flight time total : 9000 flight time type : 1641
ASRS Report	264177
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : nmac
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 0 vertical : 400
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation other

Narrative:

On approach into tys, we entered undercast at approximately 4000 ft descending to ATC assigned altitude of 3000 ft. Controller advised us of light airplane traffic Y, a tomahawk, at 12 O'clock position, 5 mi maneuvering at 2500 ft. This aircraft was located on TCASII, 5 mi scale selected but altitude readout indicated the target aircraft was at 3000 ft. Passing 3500 ft target aircraft still showed 12 O'clock position less than 1 mi at 3000. At this point, I commenced a climbing left turn. A few seconds later, TCASII RA sounded commanding a climb. While in the climb TCASII indicated target aircraft directly beneath us minus 400 ft. The entire maneuver was conducted in IMC conditions. No visual sighting of target aircraft. No avoidance vector issued by ATC. I believe starting the climb before the TCASII RA gave us an additional 200 ft of clearance from the other aircraft. Entire event occurred under positive ATC control descending on assigned heading to assigned altitude.

Original NASA ASRS Text

Title: ACR HAS NMAC WITH SMA ON APCH INTO TYS.

Narrative: ON APCH INTO TYS, WE ENTERED UNDERCAST AT APPROX 4000 FT DSNDING TO ATC ASSIGNED ALT OF 3000 FT. CTLR ADVISED US OF LIGHT AIRPLANE TFC Y, A TOMAHAWK, AT 12 O'CLOCK POS, 5 MI MANEUVERING AT 2500 FT. THIS ACFT WAS LOCATED ON TCASII, 5 MI SCALE SELECTED BUT ALT READOUT INDICATED THE TARGET ACFT WAS AT 3000 FT. PASSING 3500 FT TARGET ACFT STILL SHOWED 12 O'CLOCK POS LESS THAN 1 MI AT 3000. AT THIS POINT, I COMMENCED A CLBING L TURN. A FEW SECONDS LATER, TCASII RA SOUNDED COMMANDING A CLB. WHILE IN THE CLB TCASII INDICATED TARGET ACFT DIRECTLY BENEATH US MINUS 400 FT. THE ENTIRE MANEUVER WAS CONDUCTED IN IMC CONDITIONS. NO VISUAL SIGHTING OF TARGET ACFT. NO AVOIDANCE VECTOR ISSUED BY ATC. I BELIEVE STARTING THE CLB BEFORE THE TCASII RA GAVE US AN ADDITIONAL 200 FT OF CLRNC FROM THE OTHER ACFT. ENTIRE EVENT OCCURRED UNDER POSITIVE ATC CTL DSNDING ON ASSIGNED HDG TO ASSIGNED ALT.

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.