Narrative:

We were operating a part 121 air carrier flight. Destination was cvg airport. ZID controller told us to descend from FL270 to FL260. We acknowledged the change and initiated a descent. Instructions were 'descend and maintain FL260, 1500 FPM in the descent.' this a very high rate for only a 1000 ft change. Almost immediately after acknowledging, another voice came on the frequency and told us to descend to FL240 at 1500 f-m. We acknowledged and reset the altitude pre-selector. Almost immediately, the TCASII aural warning sounded, 'traffic, traffic.' the target appeared at 3 O'clock position and 2-3 mi. I disconnected the autoplt, manually increased the rate of descent and looked the window. An air carrier aircraft was sbound, at about FL260. At the time he passed overhead, TCASII showed 600 ft separation. Our descent rate was as high as 4000 FPM. I manually leveled the airplane at FL240 and re-engaged the autoplt. The rest of the flight was uneventful. I believe this was a controller in training. This was the second time that his voice was superseded by another (possibly a supervisor) and his instructions overridden. Either more training or closer supervision would seem appropriate. I didn't have his perspective, so I don't know what caused the conflict from his end, or what the reason was for the altitude change. It would seem that having us maintain FL270 until the crossing traffic passed would have ben safer.

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Original NASA ASRS Text

Title: CRITICAL POTENTIAL CONFLICT OCCURS WHEN ATC DSNDS A CRJ THROUGH AN ALT OCCUPIED BY A XING ACR 23 NM SW OF APE, OH.

Narrative: WE WERE OPERATING A PART 121 ACR FLT. DEST WAS CVG ARPT. ZID CTLR TOLD US TO DSND FROM FL270 TO FL260. WE ACKNOWLEDGED THE CHANGE AND INITIATED A DSCNT. INSTRUCTIONS WERE 'DSND AND MAINTAIN FL260, 1500 FPM IN THE DSCNT.' THIS A VERY HIGH RATE FOR ONLY A 1000 FT CHANGE. ALMOST IMMEDIATELY AFTER ACKNOWLEDGING, ANOTHER VOICE CAME ON THE FREQ AND TOLD US TO DSND TO FL240 AT 1500 F-M. WE ACKNOWLEDGED AND RESET THE ALT PRE-SELECTOR. ALMOST IMMEDIATELY, THE TCASII AURAL WARNING SOUNDED, 'TFC, TFC.' THE TARGET APPEARED AT 3 O'CLOCK POS AND 2-3 MI. I DISCONNECTED THE AUTOPLT, MANUALLY INCREASED THE RATE OF DSCNT AND LOOKED THE WINDOW. AN ACR ACFT WAS SBOUND, AT ABOUT FL260. AT THE TIME HE PASSED OVERHEAD, TCASII SHOWED 600 FT SEPARATION. OUR DSCNT RATE WAS AS HIGH AS 4000 FPM. I MANUALLY LEVELED THE AIRPLANE AT FL240 AND RE-ENGAGED THE AUTOPLT. THE REST OF THE FLT WAS UNEVENTFUL. I BELIEVE THIS WAS A CTLR IN TRAINING. THIS WAS THE SECOND TIME THAT HIS VOICE WAS SUPERSEDED BY ANOTHER (POSSIBLY A SUPVR) AND HIS INSTRUCTIONS OVERRIDDEN. EITHER MORE TRAINING OR CLOSER SUPERVISION WOULD SEEM APPROPRIATE. I DIDN'T HAVE HIS PERSPECTIVE, SO I DON'T KNOW WHAT CAUSED THE CONFLICT FROM HIS END, OR WHAT THE REASON WAS FOR THE ALT CHANGE. IT WOULD SEEM THAT HAVING US MAINTAIN FL270 UNTIL THE XING TFC PASSED WOULD HAVE BEN SAFER.

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.