Air carrier X TCASII RA with VFR aircraft 1500 ft below. Evasive action taken climb.

Attributes
ACN	247274
Time
Date	199304
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : ord
State Reference	IL
Altitude	msl bound lower : 3000 msl bound upper : 4000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	VFR
Person 1
Affiliation	government : faa
Function	other personnel other
Qualification	controller : radar
ASRS Report	247274
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	altitude deviation : undershoot conflict : airborne less severe non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 12000 vertical : 2100
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

Air carrier X was being vectored to runway 4R descending to 3000 ft with a VFR Y at 1900 ft below TCA at 1 O'clock and 2 mi. Air carrier X reports a RA climb and the controller advises the traffic is below 2000 ft (more than 1500 ft difference). Air carrier X climbs back to 4000 ft, then passes and descends again for the approach. Workload: low. Clearance deviation of 300 ft. Communication after the maneuver. The controller asked the pilot if his TCASII showed the target to be below 2000 ft. He indicated he did not observe that, only the climb.

Original NASA ASRS Text

Title: ACR X TCASII RA WITH VFR ACFT 1500 FT BELOW. EVASIVE ACTION TAKEN CLB.

Narrative: ACR X WAS BEING VECTORED TO RWY 4R DSNDING TO 3000 FT WITH A VFR Y AT 1900 FT BELOW TCA AT 1 O'CLOCK AND 2 MI. ACR X RPTS A RA CLB AND THE CTLR ADVISES THE TFC IS BELOW 2000 FT (MORE THAN 1500 FT DIFFERENCE). ACR X CLBS BACK TO 4000 FT, THEN PASSES AND DSNDS AGAIN FOR THE APCH. WORKLOAD: LOW. CLRNC DEV OF 300 FT. COM AFTER THE MANEUVER. THE CTLR ASKED THE PLT IF HIS TCASII SHOWED THE TARGET TO BE BELOW 2000 FT. HE INDICATED HE DID NOT OBSERVE THAT, ONLY THE CLB.

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.