Narrative:

Flying rivers arrival stl lambert airport at FL240, light turbulence began to make flight uncomfortable, so we asked ZKC if lower altitude was smoother. Controller was very busy and did not respond immediately, so I picked up the PA and was making an announcement about the choppiness. In the middle of my announcement ATC told us we had to go to FL200 or below for smoother air and the first officer and I both heard him clear us to FL200. I began a descent and finished the PA announcement, as the first officer repeated the clearance over the radio to ATC. The controller made no correction and immediately began talking to another aircraft. As I was passing FL230 the controller said he needed us at FL240 and that he had only told us the altitude we need to descend to for smooth air, not an actual clearance. The first officer responded by telling him we had been cleared to FL200. The controller told us to maintain FL230 and turned us over to another ZKC frequency with no further discussion. No conflict was observed on our part and we completed the flight with no further occurrence. Contributing factors -- if we in fact had made an error (which I don't think we did): 1) controller was so busy he missed the first officer's response to his understood clearance to descend to a lower altitude. 2) my concentration was divided between communications with ATC and making the PA announcement.

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Original NASA ASRS Text

Title: A DC9-10 CREW DSNDS OUT OF FL240 UPON 'RECEIVING A CLRNC TO FL200.' THE CTLR CAUGHT THEM AT FL230 AND ASSIGNED THAT AS A 'STOP' ALT, DISPUTING THEIR CLRNC TO FL200.

Narrative: FLYING RIVERS ARR STL LAMBERT ARPT AT FL240, LIGHT TURB BEGAN TO MAKE FLT UNCOMFORTABLE, SO WE ASKED ZKC IF LOWER ALT WAS SMOOTHER. CTLR WAS VERY BUSY AND DID NOT RESPOND IMMEDIATELY, SO I PICKED UP THE PA AND WAS MAKING AN ANNOUNCEMENT ABOUT THE CHOPPINESS. IN THE MIDDLE OF MY ANNOUNCEMENT ATC TOLD US WE HAD TO GO TO FL200 OR BELOW FOR SMOOTHER AIR AND THE FO AND I BOTH HEARD HIM CLR US TO FL200. I BEGAN A DSCNT AND FINISHED THE PA ANNOUNCEMENT, AS THE FO REPEATED THE CLRNC OVER THE RADIO TO ATC. THE CTLR MADE NO CORRECTION AND IMMEDIATELY BEGAN TALKING TO ANOTHER ACFT. AS I WAS PASSING FL230 THE CTLR SAID HE NEEDED US AT FL240 AND THAT HE HAD ONLY TOLD US THE ALT WE NEED TO DSND TO FOR SMOOTH AIR, NOT AN ACTUAL CLRNC. THE FO RESPONDED BY TELLING HIM WE HAD BEEN CLRED TO FL200. THE CTLR TOLD US TO MAINTAIN FL230 AND TURNED US OVER TO ANOTHER ZKC FREQ WITH NO FURTHER DISCUSSION. NO CONFLICT WAS OBSERVED ON OUR PART AND WE COMPLETED THE FLT WITH NO FURTHER OCCURRENCE. CONTRIBUTING FACTORS -- IF WE IN FACT HAD MADE AN ERROR (WHICH I DON'T THINK WE DID): 1) CTLR WAS SO BUSY HE MISSED THE FO'S RESPONSE TO HIS UNDERSTOOD CLRNC TO DSND TO A LOWER ALT. 2) MY CONCENTRATION WAS DIVIDED BTWN COMS WITH ATC AND MAKING THE PA ANNOUNCEMENT.

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.