Narrative:

Center had step climbed us from 10000 ft to FL190, in 1000 ft steps. At FL180, the first officer made a PA. I, the PF, took the radios. I thought I heard 'climb to FL200.' I dialed in 20000 on the altitude alerter. At about 19400 ft, center asked if we were at FL190. I said, no, we were cleared to FL200. She said, no, descend to FL190. We did. I do not know how I came to dial in FL200. We had been told by the center frequency before the one we were on to expect FL200 as a final. Perhaps with all the 'step' climbing and the 'expect FL200' I 'expected' 200 and dialed it in when she assigned FL190. My interpretation is that I made a mistake, and without the second pilot to catch it (he was making PA) the adds caught up with me. Supplemental information from acn 224501: captain turns off seat belt sign and tells me to brief passenger. I acknowledge and fully turn down volume on communication 1 and transmit on PA to cabin. Center advises us of traffic at 10 O'clock, 3 mi at FL200. I was not on communication 1 when transmissions were made.

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Original NASA ASRS Text

Title: AN ACR LTT OVERSHOT ITS ALT IN A STEP CLB SITUATION AND CAUSED AN LTSS.

Narrative: CTR HAD STEP CLBED US FROM 10000 FT TO FL190, IN 1000 FT STEPS. AT FL180, THE FO MADE A PA. I, THE PF, TOOK THE RADIOS. I THOUGHT I HEARD 'CLB TO FL200.' I DIALED IN 20000 ON THE ALT ALERTER. AT ABOUT 19400 FT, CTR ASKED IF WE WERE AT FL190. I SAID, NO, WE WERE CLRED TO FL200. SHE SAID, NO, DSND TO FL190. WE DID. I DO NOT KNOW HOW I CAME TO DIAL IN FL200. WE HAD BEEN TOLD BY THE CTR FREQ BEFORE THE ONE WE WERE ON TO EXPECT FL200 AS A FINAL. PERHAPS WITH ALL THE 'STEP' CLBING AND THE 'EXPECT FL200' I 'EXPECTED' 200 AND DIALED IT IN WHEN SHE ASSIGNED FL190. MY INTERP IS THAT I MADE A MISTAKE, AND WITHOUT THE SECOND PLT TO CATCH IT (HE WAS MAKING PA) THE ADDS CAUGHT UP WITH ME. SUPPLEMENTAL INFO FROM ACN 224501: CAPT TURNS OFF SEAT BELT SIGN AND TELLS ME TO BRIEF PAX. I ACKNOWLEDGE AND FULLY TURN DOWN VOLUME ON COM 1 AND XMIT ON PA TO CABIN. CTR ADVISES US OF TFC AT 10 O'CLOCK, 3 MI AT FL200. I WAS NOT ON COM 1 WHEN TRANSMISSIONS WERE MADE.

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.