Narrative:

I was assigned FL200 by ZAU and was at FL204 when I noticed my mistake. I was in the process of disconnecting the autoplt when ATC called and asked me to confirm my altitude assignment. I think I overshot by a total of 500 ft. The root of the problem, aside from a basic human failing, was my not trusting my altitude hold button on the autoplt. It checked ok on the preflight but, although it indicated 'on' during the climb, the autoplt didn't level off the airplane. I trusted the autoplt, got distraction trying to figure how to put a latitude/longitude waypoint into my GPS receiver (I had never before had a clearance which involved a latitude/longitude number instead of an intersection or VOR). I do have a backup altitude warning system (altitude alert), but it didn't get my attention. A personal rule of 'when turning, do nothing else' will now be extended to 'when turning or climbing to an assigned altitude, do nothing else.'

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Original NASA ASRS Text

Title: SMT PVT PLT CLBING TO ASSIGNED ALT FL200 WAS DISTR SETTING UP THE GPS WITH LATITUDE AND LONGITUDE COMPONENTS. CTLR CALLED QUESTIONING ALT ASSIGNED. RPTR CORRECTED TO FL200.

Narrative: I WAS ASSIGNED FL200 BY ZAU AND WAS AT FL204 WHEN I NOTICED MY MISTAKE. I WAS IN THE PROCESS OF DISCONNECTING THE AUTOPLT WHEN ATC CALLED AND ASKED ME TO CONFIRM MY ALT ASSIGNMENT. I THINK I OVERSHOT BY A TOTAL OF 500 FT. THE ROOT OF THE PROB, ASIDE FROM A BASIC HUMAN FAILING, WAS MY NOT TRUSTING MY ALT HOLD BUTTON ON THE AUTOPLT. IT CHKED OK ON THE PREFLT BUT, ALTHOUGH IT INDICATED 'ON' DURING THE CLB, THE AUTOPLT DIDN'T LEVEL OFF THE AIRPLANE. I TRUSTED THE AUTOPLT, GOT DISTR TRYING TO FIGURE HOW TO PUT A LATITUDE/LONGITUDE WAYPOINT INTO MY GPS RECEIVER (I HAD NEVER BEFORE HAD A CLRNC WHICH INVOLVED A LATITUDE/LONGITUDE NUMBER INSTEAD OF AN INTXN OR VOR). I DO HAVE A BACKUP ALT WARNING SYS (ALT ALERT), BUT IT DIDN'T GET MY ATTN. A PERSONAL RULE OF 'WHEN TURNING, DO NOTHING ELSE' WILL NOW BE EXTENDED TO 'WHEN TURNING OR CLBING TO AN ASSIGNED ALT, DO NOTHING ELSE.'

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.