Narrative:

Cleared to FL250, told to hold at rwf VOR. Controller gave us the holding instructions, etc, etc, as I was descending from FL270. I turned autoplt on course, the first officer dialed in FL250, and I pushed the altitude hold capture button on pedestal. Problem was, in this model that feature had been deactivated. But being a creature of habit, and the fact that we operate same model with the feature operable, the aircraft sank 500 ft below FL250. I quickly caught it and leveled at FL250. The controller didn't say anything but I called on the ground anyway. No conflict, except complacency and the use of that feature on the other airplanes, etc, didn't help. We operate 5 different models of B727 and they're not all the same.

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Original NASA ASRS Text

Title: CAPT OF AN LGT OVERSHOT DSCNT ALT DUE TO RELYING ON THE AUTOPLT ALT HOLD CAPTURE FEATURE WHICH HAD BEEN DEACTIVATED.

Narrative: CLRED TO FL250, TOLD TO HOLD AT RWF VOR. CTLR GAVE US THE HOLDING INSTRUCTIONS, ETC, ETC, AS I WAS DSNDING FROM FL270. I TURNED AUTOPLT ON COURSE, THE FO DIALED IN FL250, AND I PUSHED THE ALT HOLD CAPTURE BUTTON ON PEDESTAL. PROB WAS, IN THIS MODEL THAT FEATURE HAD BEEN DEACTIVATED. BUT BEING A CREATURE OF HABIT, AND THE FACT THAT WE OPERATE SAME MODEL WITH THE FEATURE OPERABLE, THE ACFT SANK 500 FT BELOW FL250. I QUICKLY CAUGHT IT AND LEVELED AT FL250. THE CTLR DIDN'T SAY ANYTHING BUT I CALLED ON THE GND ANYWAY. NO CONFLICT, EXCEPT COMPLACENCY AND THE USE OF THAT FEATURE ON THE OTHER AIRPLANES, ETC, DIDN'T HELP. WE OPERATE 5 DIFFERENT MODELS OF B727 AND THEY'RE NOT ALL THE SAME.

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.