An air carrier responded to a TCASII alert and descended when the intruder aircraft was in sight and radar contact and well clear with at least standard separation.

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Attributes
ACN	210233
Time
Date	199205
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : amg
State Reference	GA
Altitude	msl bound lower : 26700 msl bound upper : 27000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : ztl
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : atp pilot : commercial pilot : flight engineer
Experience	flight time last 90 days : 170 flight time total : 16000 flight time type : 3000
ASRS Report	210233
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
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 other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 12000 vertical : 6000
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation other

Narrative:

ATC advised air carrier medium large transport descending to FL280 at 12 O'clock. With medium large transport at +1500 ft on TCASII and descending at 2 mi converging, we were issued TCASII command to descend. I tried to initiate contact directly with medium large transport and was unable. Copilot initiated rapid descent and command ceased. Bottomed out at approximately FL267 after I told the copilot to 'cut the descent and level off.' the abruptness and degree of the copilot's reaction to the TCASII command I felt was too extreme for the circumstances and we discussed this. Had I not issued the other instructions immediately (or taken control of the aircraft) our descent would have been close to 1000 ft. In cases such as this, when you are virtually certain of the nature of the conflict, I advised a less abrupt and steep initial descent. As in congested terminal areas, the cure might end up worse than the ailment!

Original NASA ASRS Text

Title: AN ACR RESPONDED TO A TCASII ALERT AND DSNDED WHEN THE INTRUDER ACFT WAS IN SIGHT AND RADAR CONTACT AND WELL CLR WITH AT LEAST STANDARD SEPARATION.

Narrative: ATC ADVISED ACR MLG DSNDING TO FL280 AT 12 O'CLOCK. WITH MLG AT +1500 FT ON TCASII AND DSNDING AT 2 MI CONVERGING, WE WERE ISSUED TCASII COMMAND TO DSND. I TRIED TO INITIATE CONTACT DIRECTLY WITH MLG AND WAS UNABLE. COPLT INITIATED RAPID DSCNT AND COMMAND CEASED. BOTTOMED OUT AT APPROX FL267 AFTER I TOLD THE COPLT TO 'CUT THE DSCNT AND LEVEL OFF.' THE ABRUPTNESS AND DEG OF THE COPLT'S REACTION TO THE TCASII COMMAND I FELT WAS TOO EXTREME FOR THE CIRCUMSTANCES AND WE DISCUSSED THIS. HAD I NOT ISSUED THE OTHER INSTRUCTIONS IMMEDIATELY (OR TAKEN CTL OF THE ACFT) OUR DSCNT WOULD HAVE BEEN CLOSE TO 1000 FT. IN CASES SUCH AS THIS, WHEN YOU ARE VIRTUALLY CERTAIN OF THE NATURE OF THE CONFLICT, I ADVISED A LESS ABRUPT AND STEEP INITIAL DSCNT. AS IN CONGESTED TERMINAL AREAS, THE CURE MIGHT END UP WORSE THAN THE AILMENT!

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.