Air carrier X TCASII RA evasive action taken from air carrier Y 5000 ft lower.

Attributes
ACN	247283
Time
Date	199305
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : ord
State Reference	IL
Altitude	msl bound lower : 9000 msl bound upper : 9000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	other personnel other
Qualification	controller : radar
ASRS Report	247283
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller radar : 6
Events
Anomaly	altitude deviation : undershoot non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

Air carrier X had been cleared from 11000 ft to 7000 ft. Air carrier X reported that he was climbing for an RA 'that just went away.' the controller was not looking at air carrier X's target until he advised of this. The controller observed air carrier X mode C go from 9500 ft to 10000 ft although he could have actually been at a lower altitude. The only traffic even remotely in the area was air carrier Y 2 mi in front at 4500 ft. I think a TCASII RA initiated by traffic 5000 ft below a descending airplane constitutes a major flaw in this unit's software.

Original NASA ASRS Text

Title: ACR X TCASII RA EVASIVE ACTION TAKEN FROM ACR Y 5000 FT LOWER.

Narrative: ACR X HAD BEEN CLRED FROM 11000 FT TO 7000 FT. ACR X RPTED THAT HE WAS CLBING FOR AN RA 'THAT JUST WENT AWAY.' THE CTLR WAS NOT LOOKING AT ACR X'S TARGET UNTIL HE ADVISED OF THIS. THE CTLR OBSERVED ACR X MODE C GO FROM 9500 FT TO 10000 FT ALTHOUGH HE COULD HAVE ACTUALLY BEEN AT A LOWER ALT. THE ONLY TFC EVEN REMOTELY IN THE AREA WAS ACR Y 2 MI IN FRONT AT 4500 FT. I THINK A TCASII RA INITIATED BY TFC 5000 FT BELOW A DSNDING AIRPLANE CONSTITUTES A MAJOR FLAW IN THIS UNIT'S SOFTWARE.

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.