CL65 captain experienced TCAS TA event with ZKC at FL270 and descended below assigned altitude.

Attributes
ACN	657185
Time
Date	200505
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : irk.vortac
State Reference	MO
Altitude	msl single value : 27000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zkc.artcc
Operator	common carrier : air carrier
Make Model Name	Regional Jet CL65 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zkc.artcc
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 240 flight time total : 6050 flight time type : 2750
ASRS Report	657185
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance
Independent Detector	aircraft equipment : tcas other flight crewa
Resolutory Action	controller : issued advisory flight crew : took evasive action
Miss Distance	horizontal : 14400 vertical : 500
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	Ambiguous

Narrative:

We were level at FL270. Center called and said there would be traffic crossing overhead at FL280 (1000 ft above us). We picked up the traffic visually and on TCAS as he was coming through FL290 and saw him pass FL280 and continue his descent. As he passed FL278 and continuing his descent towards our altitude and our position; center asked him if he was going to stop at FL280. He said his clearance from a previous controller was down to FL240. By then; he was at our 1 O'clock position between 3-4 mi away and closing on us; and we had already received a TA. When it became apparent that he was not going to stop his descent and as he was about 500 ft above us and still at our 1 O'clock position coming at us; I told center that I was leaving FL270 down to FL260 for traffic. Center acknowledged. We did a shallow descent to about FL267 or FL266 until traffic was clear. Then we told center we could go back to FL270. He cleared us to FL290. Remainder was uneventful.

Original NASA ASRS Text

Title: CL65 CAPT EXPERIENCED TCAS TA EVENT WITH ZKC AT FL270 AND DSNDED BELOW ASSIGNED ALT.

Narrative: WE WERE LEVEL AT FL270. CTR CALLED AND SAID THERE WOULD BE TFC XING OVERHEAD AT FL280 (1000 FT ABOVE US). WE PICKED UP THE TFC VISUALLY AND ON TCAS AS HE WAS COMING THROUGH FL290 AND SAW HIM PASS FL280 AND CONTINUE HIS DSCNT. AS HE PASSED FL278 AND CONTINUING HIS DSCNT TOWARDS OUR ALT AND OUR POS; CTR ASKED HIM IF HE WAS GOING TO STOP AT FL280. HE SAID HIS CLRNC FROM A PREVIOUS CTLR WAS DOWN TO FL240. BY THEN; HE WAS AT OUR 1 O'CLOCK POS BTWN 3-4 MI AWAY AND CLOSING ON US; AND WE HAD ALREADY RECEIVED A TA. WHEN IT BECAME APPARENT THAT HE WAS NOT GOING TO STOP HIS DSCNT AND AS HE WAS ABOUT 500 FT ABOVE US AND STILL AT OUR 1 O'CLOCK POS COMING AT US; I TOLD CTR THAT I WAS LEAVING FL270 DOWN TO FL260 FOR TFC. CTR ACKNOWLEDGED. WE DID A SHALLOW DSCNT TO ABOUT FL267 OR FL266 UNTIL TFC WAS CLR. THEN WE TOLD CTR WE COULD GO BACK TO FL270. HE CLRED US TO FL290. REMAINDER WAS UNEVENTFUL.

Data retrieved from NASA's ASRS site as of January 2009 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.