TCASII causes large transport to descend 1000 ft without clearance.

Attributes
ACN	238177
Time
Date	199304
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : csn
State Reference	VA
Altitude	msl bound lower : 27000 msl bound upper : 28000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute airway : j48
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 4000 flight time type : 1000
ASRS Report	238177
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi pilot : commercial pilot : instrument
Experience	flight time last 90 days : 150 flight time total : 12000 flight time type : 150
ASRS Report	238440
Events
Anomaly	aircraft equipment problem : critical conflict : airborne less severe non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	controller : issued new clearance flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 6000 vertical : 1000
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Center cleared an aircraft at FL310 to FL290. This aircraft was directly above ours. We were at FL280. The descent of the other aircraft caused a TCASII RA to command descent of 2000 FPM. Since we were IMC at the time, we started an uncommanded descent to FL270 and advised ZDC of our action. Once we were at FL270 ZDC wanted to climb us back up to FL280 but the TCASII RA hadn't reset which prohibited us to climb back up. Center needs to know that if there are 2 aircraft with limited horizontal separation and one is asked to climb or descend, depend on the rate used may cause a TCASII TA/RA. All the TCASII knows is that if an aircraft is descending to within 1000 ft of another plane at a rate of 1500-2000 FPM, there is going to be a conflict. If this would have happened in VMC conditions we wouldn't have had to descend. Center should also advise us if they are descending an aircraft to within 1000 ft that is directly above us. Overall I like the TCASII system but in high flow/congested areas it can cause some problems for controllers especially in cases like ours. I'm glad there wasn't any opposite traffic at FL270 today.

Original NASA ASRS Text

Title: TCASII CAUSES LGT TO DSND 1000 FT WITHOUT CLRNC.

Narrative: CTR CLRED AN ACFT AT FL310 TO FL290. THIS ACFT WAS DIRECTLY ABOVE OURS. WE WERE AT FL280. THE DSCNT OF THE OTHER ACFT CAUSED A TCASII RA TO COMMAND DSCNT OF 2000 FPM. SINCE WE WERE IMC AT THE TIME, WE STARTED AN UNCOMMANDED DSCNT TO FL270 AND ADVISED ZDC OF OUR ACTION. ONCE WE WERE AT FL270 ZDC WANTED TO CLB US BACK UP TO FL280 BUT THE TCASII RA HADN'T RESET WHICH PROHIBITED US TO CLB BACK UP. CTR NEEDS TO KNOW THAT IF THERE ARE 2 ACFT WITH LIMITED HORIZ SEPARATION AND ONE IS ASKED TO CLB OR DSND, DEPEND ON THE RATE USED MAY CAUSE A TCASII TA/RA. ALL THE TCASII KNOWS IS THAT IF AN ACFT IS DSNDING TO WITHIN 1000 FT OF ANOTHER PLANE AT A RATE OF 1500-2000 FPM, THERE IS GOING TO BE A CONFLICT. IF THIS WOULD HAVE HAPPENED IN VMC CONDITIONS WE WOULDN'T HAVE HAD TO DSND. CTR SHOULD ALSO ADVISE US IF THEY ARE DSNDING AN ACFT TO WITHIN 1000 FT THAT IS DIRECTLY ABOVE US. OVERALL I LIKE THE TCASII SYS BUT IN HIGH FLOW/CONGESTED AREAS IT CAN CAUSE SOME PROBS FOR CTLRS ESPECIALLY IN CASES LIKE OURS. I'M GLAD THERE WASN'T ANY OPPOSITE TFC AT FL270 TODAY.

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.