Potential conflict with unknown VFR NORAC traffic.

Attributes
ACN	279412
Time
Date	199407
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : jvl
State Reference	WI
Altitude	msl bound lower : 10500 msl bound upper : 12300
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent other
Route In Use	arrival other arrival star : star enroute airway : ord
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Flight Phase	cruise other
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 300 flight time total : 13000 flight time type : 300
ASRS Report	279412
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 6000 vertical : 500
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Flight en route lnk-ord was cleared janesville III arrival with clearance to cross teddy intersection at 10000 ft. Approaching teddy intersection descending through 10700 ft, ord ATC advised of VFR traffic ahead, no radio contact, suggested we maintain 11000 ft. We climbed back to 11000 ft, and shortly received TCASII alert 'traffic, traffic,' and target appeared on screen at 1 O'clock position. Almost immediately received RA alert 'climb, climb.' I immediately raised nose, applying climb power, and climbed. At above 12300 ft the TCASII alert subsided and we observed the red TCASII DOT on screen passing on r-hand side at about 1 mi on screen, followed by 'clear of conflict' alert. Neither the first officer nor myself were ever able to establish a visual on the target. Continued on for normal arrival at ord.

Original NASA ASRS Text

Title: POTENTIAL CONFLICT WITH UNKNOWN VFR NORAC TFC.

Narrative: FLT ENRTE LNK-ORD WAS CLRED JANESVILLE III ARR WITH CLRNC TO CROSS TEDDY INTXN AT 10000 FT. APCHING TEDDY INTXN DSNDING THROUGH 10700 FT, ORD ATC ADVISED OF VFR TFC AHEAD, NO RADIO CONTACT, SUGGESTED WE MAINTAIN 11000 FT. WE CLBED BACK TO 11000 FT, AND SHORTLY RECEIVED TCASII ALERT 'TFC, TFC,' AND TARGET APPEARED ON SCREEN AT 1 O'CLOCK POS. ALMOST IMMEDIATELY RECEIVED RA ALERT 'CLB, CLB.' I IMMEDIATELY RAISED NOSE, APPLYING CLB PWR, AND CLBED. AT ABOVE 12300 FT THE TCASII ALERT SUBSIDED AND WE OBSERVED THE RED TCASII DOT ON SCREEN PASSING ON R-HAND SIDE AT ABOUT 1 MI ON SCREEN, FOLLOWED BY 'CLR OF CONFLICT' ALERT. NEITHER THE FO NOR MYSELF WERE EVER ABLE TO ESTABLISH A VISUAL ON THE TARGET. CONTINUED ON FOR NORMAL ARR AT ORD.

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.