Controller report of TCASII RA in which flight crew responded. Altitude deviation.

Attributes
ACN	232487
Time
Date	199301
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : clt
State Reference	NC
Altitude	msl bound lower : 9400 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : n90
Operator	common carrier : air carrier
Make Model Name	Medium Transport, High Wing, 2 Turboprop Eng
Navigation In Use	Other
Flight Phase	cruise other
Route In Use	enroute airway : gso
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
ASRS Report	232487
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	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	other

Narrative:

I was working arrival radar east and accepted a handoff on air carrier X at 10000 ft. A few moments later I accepted a handoff on air carrier Y descending to 11000 ft. When air carrier X checked in I advised him of air carrier Y position, which was 6 O'clock and 2 NM, and that he was descending to 11000 ft. A few moments later air carrier X advised me he was descending because of a TCASII advisory he had just received. I then observed air carrier X descend from 10000 ft to 9400 ft. Air carrier Y leveled off at 11000 ft. This deviation occurred outside of my control boundary in gso approach airspace. Comment: TCASII should only be used as an advisory tool for pilots and should not override ATC instructions. The pilot of an aircraft should be able to determine if a TCASII instruction should be followed, especially when ATC just issued the traffic involved and what to expect. Until that happens we can only expect more problems from TCASII.

Original NASA ASRS Text

Title: CTLR RPT OF TCASII RA IN WHICH FLC RESPONDED. ALTDEV.

Narrative: I WAS WORKING ARR RADAR E AND ACCEPTED A HDOF ON ACR X AT 10000 FT. A FEW MOMENTS LATER I ACCEPTED A HDOF ON ACR Y DSNDING TO 11000 FT. WHEN ACR X CHKED IN I ADVISED HIM OF ACR Y POS, WHICH WAS 6 O'CLOCK AND 2 NM, AND THAT HE WAS DSNDING TO 11000 FT. A FEW MOMENTS LATER ACR X ADVISED ME HE WAS DSNDING BECAUSE OF A TCASII ADVISORY HE HAD JUST RECEIVED. I THEN OBSERVED ACR X DSND FROM 10000 FT TO 9400 FT. ACR Y LEVELED OFF AT 11000 FT. THIS DEV OCCURRED OUTSIDE OF MY CTL BOUNDARY IN GSO APCH AIRSPACE. COMMENT: TCASII SHOULD ONLY BE USED AS AN ADVISORY TOOL FOR PLTS AND SHOULD NOT OVERRIDE ATC INSTRUCTIONS. THE PLT OF AN ACFT SHOULD BE ABLE TO DETERMINE IF A TCASII INSTRUCTION SHOULD BE FOLLOWED, ESPECIALLY WHEN ATC JUST ISSUED THE TFC INVOLVED AND WHAT TO EXPECT. UNTIL THAT HAPPENS WE CAN ONLY EXPECT MORE PROBS FROM TCASII.

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.