Narrative:

Early morning (middle of the night) air ambiguity flight, single pilot. WX very good, VMC entire trip. Short (35 min) leg each way to retrieve patient and bring back to ZZZ. On return leg to ZZZ, center cleared me to descend at discretion from FL210 to 16000 ft, approximately 80 NM south of airport ZZZ. About 50 NM south I began descent and advised center. About 40 NM south, center asked me to contact approach on 118.3 (everything on tower frequency, this time of day XA00 local). I was listening to ATIS at the same time. I acknowledged center and continued to listen to ATIS which was advertising visuals to runway 03, which I was expecting. I reset my altitude alerter to indicate 'cleared for visual approach' erroneously. I checked in with tower and approach. Told him I was descending for runway 3. When he asked my assigned altitude, I knew something was wrong. I was now about 14000 ft and last clearance was 16000 ft. Uneventful approach and landing followed. No conflicts or loss of separation. Primary factors: time of day: very tired, far below 100 percent mental alertness. It even took me a while to figure out what I had done. Others: expectations and complacency. Excellent WX, very familiar with all aspects of this flight. Airport (and expected runway) in sight for a long time. I mentally repeated 'visual runway 3' when I heard it on ATIS and proceeded to do that, altitude wise. There was not a course deviation as the course to the VOR set me up for runway 3 (also a contributor). Corrective: exercise extreme vigilance when operating aircraft at times you should be and normally would be sleeping. Be alert for 'expectation errors' when everything is familiar.

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Original NASA ASRS Text

Title: AN AIR AMBULANCE FLT DSNDING TO 16000 FT AND ANTICIPATING A VISUAL APCH, CONTINUES DSCNT THROUGH 16000 FT. THE CTLR QUESTIONS THE PLT ABOUT HIS ALT AT 14000 FT. THE REMAINDER OF THE APCH AND LNDG WAS UNEVENTFUL.

Narrative: EARLY MORNING (MIDDLE OF THE NIGHT) AIR AMB FLT, SINGLE PLT. WX VERY GOOD, VMC ENTIRE TRIP. SHORT (35 MIN) LEG EACH WAY TO RETRIEVE PATIENT AND BRING BACK TO ZZZ. ON RETURN LEG TO ZZZ, CTR CLRED ME TO DSND AT DISCRETION FROM FL210 TO 16000 FT, APPROX 80 NM S OF ARPT ZZZ. ABOUT 50 NM S I BEGAN DSCNT AND ADVISED CTR. ABOUT 40 NM S, CTR ASKED ME TO CONTACT APCH ON 118.3 (EVERYTHING ON TWR FREQ, THIS TIME OF DAY XA00 LCL). I WAS LISTENING TO ATIS AT THE SAME TIME. I ACKNOWLEDGED CTR AND CONTINUED TO LISTEN TO ATIS WHICH WAS ADVERTISING VISUALS TO RWY 03, WHICH I WAS EXPECTING. I RESET MY ALT ALERTER TO INDICATE 'CLRED FOR VISUAL APCH' ERRONEOUSLY. I CHKED IN WITH TWR AND APCH. TOLD HIM I WAS DSNDING FOR RWY 3. WHEN HE ASKED MY ASSIGNED ALT, I KNEW SOMETHING WAS WRONG. I WAS NOW ABOUT 14000 FT AND LAST CLRNC WAS 16000 FT. UNEVENTFUL APCH AND LNDG FOLLOWED. NO CONFLICTS OR LOSS OF SEPARATION. PRIMARY FACTORS: TIME OF DAY: VERY TIRED, FAR BELOW 100 PERCENT MENTAL ALERTNESS. IT EVEN TOOK ME A WHILE TO FIGURE OUT WHAT I HAD DONE. OTHERS: EXPECTATIONS AND COMPLACENCY. EXCELLENT WX, VERY FAMILIAR WITH ALL ASPECTS OF THIS FLT. ARPT (AND EXPECTED RWY) IN SIGHT FOR A LONG TIME. I MENTALLY REPEATED 'VISUAL RWY 3' WHEN I HEARD IT ON ATIS AND PROCEEDED TO DO THAT, ALT WISE. THERE WAS NOT A COURSE DEV AS THE COURSE TO THE VOR SET ME UP FOR RWY 3 (ALSO A CONTRIBUTOR). CORRECTIVE: EXERCISE EXTREME VIGILANCE WHEN OPERATING ACFT AT TIMES YOU SHOULD BE AND NORMALLY WOULD BE SLEEPING. BE ALERT FOR 'EXPECTATION ERRORS' WHEN EVERYTHING IS FAMILIAR.

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.