Narrative:

While descending to FL330 from FL350 I inadvertently bumped profile due to light chop, when I intended to select level change mode. We were in a vertical speed descent at the time. As a result, the autoplt locked up in all 3 modes. Therefore passing FL340 I disconnected the autoplt and reset the flight directors and ended up in vertical speed. At that time I also dropped all my flight papers on the floor as altitude capture annunciated. As I reached down, attempting to keep an eye on the aircraft, my first officer informed me that the aircraft was not leveling off even though in altitude capture. I sat up and began to pull back but due to the descent rate and my reluctance to increase G onset with a rapid pull, we bottomed out at 450 ft below the assigned altitude. I was not pleased by my performance though ATC indicated there was no problem with the missed leveloff and shortly reassigned us lower. In this instance rather than fooling with the switches, I should have disconnected and hand-flown the leveloff. I also should not have bothered with the dropped flight papers, which likely cost me 100-150 ft in the missed leveloff. It was just one of those things at the end of a long day. I have been flying EFIS aircraft for 12 yrs and certainly know better. It's a lesson I don't plan to forget.

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Original NASA ASRS Text

Title: FK100 ACFT IN DSCNT. RPTR CAPT INADVERTENTLY BUMPED PROFILE DUE TO LIGHT CHOP, AND BECAUSE AUTOPLT WAS LOCKED UP, THE RPTR DISCONNECTED THE AUTOPLT AND RESET THE FLT DIRECTORS, WHICH REMOVED THE ALT CAPTURE AND ACFT DSNDED 450 FT BELOW ASSIGNED.

Narrative: WHILE DSNDING TO FL330 FROM FL350 I INADVERTENTLY BUMPED PROFILE DUE TO LIGHT CHOP, WHEN I INTENDED TO SELECT LEVEL CHANGE MODE. WE WERE IN A VERT SPD DSCNT AT THE TIME. AS A RESULT, THE AUTOPLT LOCKED UP IN ALL 3 MODES. THEREFORE PASSING FL340 I DISCONNECTED THE AUTOPLT AND RESET THE FLT DIRECTORS AND ENDED UP IN VERT SPD. AT THAT TIME I ALSO DROPPED ALL MY FLT PAPERS ON THE FLOOR AS ALT CAPTURE ANNUNCIATED. AS I REACHED DOWN, ATTEMPTING TO KEEP AN EYE ON THE ACFT, MY FO INFORMED ME THAT THE ACFT WAS NOT LEVELING OFF EVEN THOUGH IN ALT CAPTURE. I SAT UP AND BEGAN TO PULL BACK BUT DUE TO THE DSCNT RATE AND MY RELUCTANCE TO INCREASE G ONSET WITH A RAPID PULL, WE BOTTOMED OUT AT 450 FT BELOW THE ASSIGNED ALT. I WAS NOT PLEASED BY MY PERFORMANCE THOUGH ATC INDICATED THERE WAS NO PROB WITH THE MISSED LEVELOFF AND SHORTLY REASSIGNED US LOWER. IN THIS INSTANCE RATHER THAN FOOLING WITH THE SWITCHES, I SHOULD HAVE DISCONNECTED AND HAND-FLOWN THE LEVELOFF. I ALSO SHOULD NOT HAVE BOTHERED WITH THE DROPPED FLT PAPERS, WHICH LIKELY COST ME 100-150 FT IN THE MISSED LEVELOFF. IT WAS JUST ONE OF THOSE THINGS AT THE END OF A LONG DAY. I HAVE BEEN FLYING EFIS ACFT FOR 12 YRS AND CERTAINLY KNOW BETTER. IT'S A LESSON I DON'T PLAN TO FORGET.

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.