Narrative:

25 mins into a 35 min flight, all uneventful, including even ATC. Then, cleared to 9000 ft MSL, 10 mi from a sea level field. We were approaching downwind with the field in sight and good visibility. I was flying and first officer was on the radios. I was looking outside a lot due to the good visibility. We were high, in my opinion, for our position so close to the field. I started to slow in anticipation of further descent. Next, we both hear the altitude alert tone. The first officer said '1000 ft to go' automatically. I see 8700 ft on the altimeter. I start to correct back to 9000 ft, and almost immediately ATC calls on the radio to query our altitude and clearance. We probably reached 8500 ft prior to reversing descent. It seems this is one of those multiple cause incidents: I was superconfident with my flying on this day. The first officer had a habit of not really watching close while the other pilot was flying. He is very competent and experienced and seems to never make a blunder. I guess he thought I wouldn't make one. I should have gotten him more involved as a 'copilot' sooner. All of our airplanes have an altitude alert at 300 ft past the set altitude. Wouldn't 100 ft be more appropriate for a warning? I will remember this: fly, don't anticipate a clearance just because you are in need of one.

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Original NASA ASRS Text

Title: WHILE ONLY 10 NM FROM THE DEST AND ON A HIGH DOWNWIND, AN ACR CAPT RPTS ACTING ON A CLRNC THAT HE ANTICIPATED. ALTDEV ALT OVERSHOT.

Narrative: 25 MINS INTO A 35 MIN FLT, ALL UNEVENTFUL, INCLUDING EVEN ATC. THEN, CLRED TO 9000 FT MSL, 10 MI FROM A SEA LEVEL FIELD. WE WERE APCHING DOWNWIND WITH THE FIELD IN SIGHT AND GOOD VISIBILITY. I WAS FLYING AND FO WAS ON THE RADIOS. I WAS LOOKING OUTSIDE A LOT DUE TO THE GOOD VISIBILITY. WE WERE HIGH, IN MY OPINION, FOR OUR POS SO CLOSE TO THE FIELD. I STARTED TO SLOW IN ANTICIPATION OF FURTHER DSCNT. NEXT, WE BOTH HEAR THE ALT ALERT TONE. THE FO SAID '1000 FT TO GO' AUTOMATICALLY. I SEE 8700 FT ON THE ALTIMETER. I START TO CORRECT BACK TO 9000 FT, AND ALMOST IMMEDIATELY ATC CALLS ON THE RADIO TO QUERY OUR ALT AND CLRNC. WE PROBABLY REACHED 8500 FT PRIOR TO REVERSING DSCNT. IT SEEMS THIS IS ONE OF THOSE MULTIPLE CAUSE INCIDENTS: I WAS SUPERCONFIDENT WITH MY FLYING ON THIS DAY. THE FO HAD A HABIT OF NOT REALLY WATCHING CLOSE WHILE THE OTHER PLT WAS FLYING. HE IS VERY COMPETENT AND EXPERIENCED AND SEEMS TO NEVER MAKE A BLUNDER. I GUESS HE THOUGHT I WOULDN'T MAKE ONE. I SHOULD HAVE GOTTEN HIM MORE INVOLVED AS A 'COPLT' SOONER. ALL OF OUR AIRPLANES HAVE AN ALT ALERT AT 300 FT PAST THE SET ALT. WOULDN'T 100 FT BE MORE APPROPRIATE FOR A WARNING? I WILL REMEMBER THIS: FLY, DON'T ANTICIPATE A CLRNC JUST BECAUSE YOU ARE IN NEED OF ONE.

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.