Air carrier reacting to TCASII on a VFR aircraft above, descends towards an IFR aircraft below.

Attributes
ACN	233182
Time
Date	199302
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : ord
State Reference	IL
Altitude	msl bound lower : 8000 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other descent : approach
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Light Transport, High Wing, 2 Turboprop Eng
Flight Phase	descent : approach descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller radar : 10
ASRS Report	233182
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	none taken : unable
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation other

Narrative:

Air carrier X was contacting me from the feeder controller. There was a VFR aircraft at 10500 MSL, aircraft Z, in same location. Also, there was air carrier Y, an light transport, directly below him descending out of 8000 MSL. Air carrier X was level at 10000. Air carrier X checked in on the frequency declaring that he was responding to an RA. He advised he had descended and that he was returning to his assigned altitude. This was a particularly dangerous situation. Air carrier X apparently had maneuvered when he was between frequencys. Had a control action been necessary, it would not have been possible. Additionally, because the ARTS tags had merged, the current altitude data was unavailable to me. I, by chance, noticed air carrier Y was leaving 8000 just before air carrier X checked in and the tags merged. (Also, air carrier Y was on another controller frequency that was vectoring him to a different runway. During this situation at ord, air carrier Y was on another control symbol. Air carrier Y's original assigned altitude was 9000 ft MSL. Additionally, the flight progress strip on air carrier X had a '10' on it. This advised me to not descend below 10000 until further advised by my handoff man.) I feel that the TCASII maneuver to miss a VFR aircraft (which was standard separation above him) was unnecessary and created undue stress on myself. TCASII is not aware of VFR traffic vs IFR traffic and would create a 'split the difference' situation given a VFR 500 ft above and an IFR 1000 ft below. TCASII was supposed to enhance safety, not jeopardize it.

Original NASA ASRS Text

Title: ACR REACTING TO TCASII ON A VFR ACFT ABOVE, DSNDS TOWARDS AN IFR ACFT BELOW.

Narrative: ACR X WAS CONTACTING ME FROM THE FEEDER CTLR. THERE WAS A VFR ACFT AT 10500 MSL, ACFT Z, IN SAME LOCATION. ALSO, THERE WAS ACR Y, AN LTT, DIRECTLY BELOW HIM DSNDING OUT OF 8000 MSL. ACR X WAS LEVEL AT 10000. ACR X CHKED IN ON THE FREQ DECLARING THAT HE WAS RESPONDING TO AN RA. HE ADVISED HE HAD DSNDED AND THAT HE WAS RETURNING TO HIS ASSIGNED ALT. THIS WAS A PARTICULARLY DANGEROUS SIT. ACR X APPARENTLY HAD MANEUVERED WHEN HE WAS BTWN FREQS. HAD A CTL ACTION BEEN NECESSARY, IT WOULD NOT HAVE BEEN POSSIBLE. ADDITIONALLY, BECAUSE THE ARTS TAGS HAD MERGED, THE CURRENT ALT DATA WAS UNAVAILABLE TO ME. I, BY CHANCE, NOTICED ACR Y WAS LEAVING 8000 JUST BEFORE ACR X CHKED IN AND THE TAGS MERGED. (ALSO, ACR Y WAS ON ANOTHER CTLR FREQ THAT WAS VECTORING HIM TO A DIFFERENT RWY. DURING THIS SIT AT ORD, ACR Y WAS ON ANOTHER CTL SYMBOL. ACR Y'S ORIGINAL ASSIGNED ALT WAS 9000 FT MSL. ADDITIONALLY, THE FLT PROGRESS STRIP ON ACR X HAD A '10' ON IT. THIS ADVISED ME TO NOT DSND BELOW 10000 UNTIL FURTHER ADVISED BY MY HDOF MAN.) I FEEL THAT THE TCASII MANEUVER TO MISS A VFR ACFT (WHICH WAS STANDARD SEPARATION ABOVE HIM) WAS UNNECESSARY AND CREATED UNDUE STRESS ON MYSELF. TCASII IS NOT AWARE OF VFR TFC VS IFR TFC AND WOULD CREATE A 'SPLIT THE DIFFERENCE' SIT GIVEN A VFR 500 FT ABOVE AND AN IFR 1000 FT BELOW. TCASII WAS SUPPOSED TO ENHANCE SAFETY, NOT JEOPARDIZE IT.

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.