Narrative:

We were flying mci to foe cruising at 6000 ft. My copilot was flying. I left center frequency to make the required in-range call to company at foe and the required passenger 'before landing' briefing. My copilot was monitoring center and it was his understanding that we were cleared from 6000 ft MSL to 4000 ft MSL. However, at the time, unknown to me, some of my side tone was 'bleeding' over into his headset making it difficult for him to hear. (I later squawked this complaint as reported after this to me by him.) however, he said he is certain we were cleared to 4000 ft MSL, and he had read back 4000 ft MSL to ZKC. This altitude (4000 ft) was entered and set into our altitude alerter. As we descended through 4300 ft MSL, center questioned our altitude assignment and said he (center) was of the opinion that we had only been cleared to 5000 ft MSL. We again told him that we (my copilot) had read back 4000 ft. As mentioned previously, I was off frequency during these xmissions and relied on his record of events during the brief time I was off.

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Original NASA ASRS Text

Title: FLC OF AN LTT ACR ACFT OVERSHOT DSCNT ALT ASSIGNMENT DUE TO A MISUNDERSTANDING OF CLRNC.

Narrative: WE WERE FLYING MCI TO FOE CRUISING AT 6000 FT. MY COPLT WAS FLYING. I LEFT CTR FREQ TO MAKE THE REQUIRED IN-RANGE CALL TO COMPANY AT FOE AND THE REQUIRED PAX 'BEFORE LNDG' BRIEFING. MY COPLT WAS MONITORING CTR AND IT WAS HIS UNDERSTANDING THAT WE WERE CLRED FROM 6000 FT MSL TO 4000 FT MSL. HOWEVER, AT THE TIME, UNKNOWN TO ME, SOME OF MY SIDE TONE WAS 'BLEEDING' OVER INTO HIS HEADSET MAKING IT DIFFICULT FOR HIM TO HEAR. (I LATER SQUAWKED THIS COMPLAINT AS RPTED AFTER THIS TO ME BY HIM.) HOWEVER, HE SAID HE IS CERTAIN WE WERE CLRED TO 4000 FT MSL, AND HE HAD READ BACK 4000 FT MSL TO ZKC. THIS ALT (4000 FT) WAS ENTERED AND SET INTO OUR ALT ALERTER. AS WE DSNDED THROUGH 4300 FT MSL, CTR QUESTIONED OUR ALT ASSIGNMENT AND SAID HE (CTR) WAS OF THE OPINION THAT WE HAD ONLY BEEN CLRED TO 5000 FT MSL. WE AGAIN TOLD HIM THAT WE (MY COPLT) HAD READ BACK 4000 FT. AS MENTIONED PREVIOUSLY, I WAS OFF FREQ DURING THESE XMISSIONS AND RELIED ON HIS RECORD OF EVENTS DURING THE BRIEF TIME I WAS OFF.

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.