Narrative:

Proceeding direct to anx VOR on 160 degree right, 80 mi from VOR, was given pilot's discretion to descend from FL350 to FL280. I did not start descent. Several mins later, was given clearance to descend to FL240 by ZKC. I started descent at that time. Rate of descent, about 4000 FPM. At FL250 I noticed traffic Y on TCAS screen at 1000' below us and 7 mi ahead at 1 O'clock position. As we leveled at FL240, traffic Y on TCAS screen changed to yellow and TA was issued by TCAS. Seconds later, TA changed to RA. At same time, traffic Y was visually idented at 1 O'clock and 1-2 mi. I started a left turn to visually avoid traffic. As TCAS RA was telling us to 'descend' to avoid conflict traffic Y, ZKC was questioning our altitude and telling us we were only cleared to FL250, not FL240, and there was traffic at FL240, 12 O'clock and 1 mi. ZKC then told us to make an immediate 90 degree left turn to avoid traffic Y. I continued left turn, climbed back up to FL250 as instructed by center. Conflict traffic continued behind and to the right of us. ZKC restated we were only cleared to FL250. We were then cleared back direct to anx VOR and given a frequency change. TCAS system operated normally and provided sufficient time to visually identify conflict traffic. TCAS was initially set on 30 mi range in normal position. ZKC area manager was contacted to find out what was actually said by controller to pilots. Tapes revealed controller made operational error and had cleared us to FL240, not FL250 as he had thought. TCAS system worth its weight in gold. Supplemental information from acn 173449: 2 aircraft in proximity of one another at the same altitude is serious indeed; however, the operating TCAS gave sufficient notice to acquire visibility contact and facilitate correct course and altitude change. TCAS addresses this problem admirably--the advanced warning allowed corrections to be applied in a timely manner, making this a manageable situation.

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Original NASA ASRS Text

Title: LESS THAN LEGAL SEPARATION FOR 2 ACFT IN ZKC PCA.

Narrative: PROCEEDING DIRECT TO ANX VOR ON 160 DEG R, 80 MI FROM VOR, WAS GIVEN PLT'S DISCRETION TO DSND FROM FL350 TO FL280. I DID NOT START DSNT. SEVERAL MINS LATER, WAS GIVEN CLRNC TO DSND TO FL240 BY ZKC. I STARTED DSNT AT THAT TIME. RATE OF DSNT, ABOUT 4000 FPM. AT FL250 I NOTICED TFC Y ON TCAS SCREEN AT 1000' BELOW US AND 7 MI AHEAD AT 1 O'CLOCK POS. AS WE LEVELED AT FL240, TFC Y ON TCAS SCREEN CHANGED TO YELLOW AND TA WAS ISSUED BY TCAS. SECS LATER, TA CHANGED TO RA. AT SAME TIME, TFC Y WAS VISUALLY IDENTED AT 1 O'CLOCK AND 1-2 MI. I STARTED A LEFT TURN TO VISUALLY AVOID TFC. AS TCAS RA WAS TELLING US TO 'DSND' TO AVOID CONFLICT TFC Y, ZKC WAS QUESTIONING OUR ALT AND TELLING US WE WERE ONLY CLRED TO FL250, NOT FL240, AND THERE WAS TFC AT FL240, 12 O'CLOCK AND 1 MI. ZKC THEN TOLD US TO MAKE AN IMMEDIATE 90 DEG LEFT TURN TO AVOID TFC Y. I CONTINUED LEFT TURN, CLBED BACK UP TO FL250 AS INSTRUCTED BY CENTER. CONFLICT TFC CONTINUED BEHIND AND TO THE RIGHT OF US. ZKC RESTATED WE WERE ONLY CLRED TO FL250. WE WERE THEN CLRED BACK DIRECT TO ANX VOR AND GIVEN A FREQ CHANGE. TCAS SYS OPERATED NORMALLY AND PROVIDED SUFFICIENT TIME TO VISUALLY IDENT CONFLICT TFC. TCAS WAS INITIALLY SET ON 30 MI RANGE IN NORMAL POS. ZKC AREA MGR WAS CONTACTED TO FIND OUT WHAT WAS ACTUALLY SAID BY CTLR TO PLTS. TAPES REVEALED CTLR MADE OPERROR AND HAD CLRED US TO FL240, NOT FL250 AS HE HAD THOUGHT. TCAS SYS WORTH ITS WEIGHT IN GOLD. SUPPLEMENTAL INFO FROM ACN 173449: 2 ACFT IN PROX OF ONE ANOTHER AT THE SAME ALT IS SERIOUS INDEED; HOWEVER, THE OPERATING TCAS GAVE SUFFICIENT NOTICE TO ACQUIRE VIS CONTACT AND FACILITATE CORRECT COURSE AND ALT CHANGE. TCAS ADDRESSES THIS PROB ADMIRABLY--THE ADVANCED WARNING ALLOWED CORRECTIONS TO BE APPLIED IN A TIMELY MANNER, MAKING THIS A MANAGEABLE SITUATION.

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.