Narrative:

While level at assigned intermediate altitude, during climb to 12000', controller was head by both my copilot and I to say, 'climb to FL220.' my copilot read back 'FL220,' and set 22000' in the altitude alerter. After leveling at FL220 and flying at that altitude for a period of time, controller asked for our altitude. Copilot responded, 'FL220.' controller stated we were cleared to FL200. My copilot responded we had heard FL220 and read back FL220. Controller responded to the effect, 'I missed that--no problem--remain FL220.' (I had filed for an en route altitude of FL220.) my concerns: if in fact the controller had assigned us FL200 and did not catch our FL220 readback, why would he not have brought the altitude difference to our attention prior to level off and continued flight at FL220? We were radar contact with operating mode C and climbing at less than 1000 FPM. Traffic seemed very light and we may have been the only aircraft being worked in our area. My recommendation is that if a controller becomes aware of a deviation from what he thinks was assigned, the flight should be notified at once and not allowed to continue as though everything is proceeding as cleared. I think safety is greatly enhanced by pilots and controllers working closely together and helping each other to make their jobs easier and safer. I make it my operating practice to help controllers and cooperate with them 100% of the time, and I would like to think that as they monitor my flts, that they are doing the same for me.

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Original NASA ASRS Text

Title: ALT DEVIATION.

Narrative: WHILE LEVEL AT ASSIGNED INTERMEDIATE ALT, DURING CLB TO 12000', CTLR WAS HEAD BY BOTH MY COPLT AND I TO SAY, 'CLB TO FL220.' MY COPLT READ BACK 'FL220,' AND SET 22000' IN THE ALT ALERTER. AFTER LEVELING AT FL220 AND FLYING AT THAT ALT FOR A PERIOD OF TIME, CTLR ASKED FOR OUR ALT. COPLT RESPONDED, 'FL220.' CTLR STATED WE WERE CLRED TO FL200. MY COPLT RESPONDED WE HAD HEARD FL220 AND READ BACK FL220. CTLR RESPONDED TO THE EFFECT, 'I MISSED THAT--NO PROB--REMAIN FL220.' (I HAD FILED FOR AN ENRTE ALT OF FL220.) MY CONCERNS: IF IN FACT THE CTLR HAD ASSIGNED US FL200 AND DID NOT CATCH OUR FL220 READBACK, WHY WOULD HE NOT HAVE BROUGHT THE ALT DIFFERENCE TO OUR ATTN PRIOR TO LEVEL OFF AND CONTINUED FLT AT FL220? WE WERE RADAR CONTACT WITH OPERATING MODE C AND CLBING AT LESS THAN 1000 FPM. TFC SEEMED VERY LIGHT AND WE MAY HAVE BEEN THE ONLY ACFT BEING WORKED IN OUR AREA. MY RECOMMENDATION IS THAT IF A CTLR BECOMES AWARE OF A DEVIATION FROM WHAT HE THINKS WAS ASSIGNED, THE FLT SHOULD BE NOTIFIED AT ONCE AND NOT ALLOWED TO CONTINUE AS THOUGH EVERYTHING IS PROCEEDING AS CLRED. I THINK SAFETY IS GREATLY ENHANCED BY PLTS AND CTLRS WORKING CLOSELY TOGETHER AND HELPING EACH OTHER TO MAKE THEIR JOBS EASIER AND SAFER. I MAKE IT MY OPERATING PRACTICE TO HELP CTLRS AND COOPERATE WITH THEM 100% OF THE TIME, AND I WOULD LIKE TO THINK THAT AS THEY MONITOR MY FLTS, THAT THEY ARE DOING THE SAME FOR ME.

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.