Narrative:

I was northbound at 4000' on V23, about 7 NM south of the btg VOR, when I was cleared for the VOR a approach to pdx. I also received an altitude restriction which I interpreted as 'cross the VOR outbnd at 4100'.' I climbed to 4100' and crossed btg. After checking the approach plate, I started a descent to 2400', proceeded about 6 NM north and started the procedure turn. At this point approach called, asking me to verify altitude. I responded with '3200', descending.' the controller informed me that I had been told to 'maintain 4100' until procedure turn inbound.' I responded with my interpretation of the clearance and began a climb while in the turn. There were no further communications re: this situation. I checked the plate again and found, to my chagrin, that the procedure actually calls for maintaining at or above 4100' until procedure turn inbound, then descending to 2400'. Upon reflection, I tried to determine what had caused me to make such a mess of an approach with which I was extremely familiar. 1) in the past, I had generally approached btg at 5000' or higher, so I was primed for a descent upon reaching the VOR. 2) I apparently misread the chart, substituting the procedure turn inbound altitude for the procedure turn altitude. 3) the flight had gone entirely too smoothly up to this point. I had been able to contact approach on the ground for departure from my home field (instead of relaying through clearance delivery), I was released immediately for departure, and approach indicated they could accommodate my requests west/O modification or delays. (Any one of these constitutes a minor miracle!) I was lulled into complacency, everything going perfectly, headed for an approach that I had flown dozens of times west/O problems. None of these, however, were sufficient grounds for giving my brain the rest of the day off, which I obviously did.

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Original NASA ASRS Text

Title: PLT OF SMA IN IMC DESCENDED BELOW PUBLISHED APCH ALT RESTRICTION.

Narrative: I WAS NBOUND AT 4000' ON V23, ABOUT 7 NM S OF THE BTG VOR, WHEN I WAS CLRED FOR THE VOR A APCH TO PDX. I ALSO RECEIVED AN ALT RESTRICTION WHICH I INTERPRETED AS 'CROSS THE VOR OUTBND AT 4100'.' I CLBED TO 4100' AND CROSSED BTG. AFTER CHKING THE APCH PLATE, I STARTED A DSCNT TO 2400', PROCEEDED ABOUT 6 NM N AND STARTED THE PROC TURN. AT THIS POINT APCH CALLED, ASKING ME TO VERIFY ALT. I RESPONDED WITH '3200', DSNDING.' THE CTLR INFORMED ME THAT I HAD BEEN TOLD TO 'MAINTAIN 4100' UNTIL PROC TURN INBND.' I RESPONDED WITH MY INTERP OF THE CLRNC AND BEGAN A CLB WHILE IN THE TURN. THERE WERE NO FURTHER COMS RE: THIS SITUATION. I CHKED THE PLATE AGAIN AND FOUND, TO MY CHAGRIN, THAT THE PROC ACTUALLY CALLS FOR MAINTAINING AT OR ABOVE 4100' UNTIL PROC TURN INBND, THEN DSNDING TO 2400'. UPON REFLECTION, I TRIED TO DETERMINE WHAT HAD CAUSED ME TO MAKE SUCH A MESS OF AN APCH WITH WHICH I WAS EXTREMELY FAMILIAR. 1) IN THE PAST, I HAD GENERALLY APCHED BTG AT 5000' OR HIGHER, SO I WAS PRIMED FOR A DSCNT UPON REACHING THE VOR. 2) I APPARENTLY MISREAD THE CHART, SUBSTITUTING THE PROC TURN INBOUND ALT FOR THE PROC TURN ALT. 3) THE FLT HAD GONE ENTIRELY TOO SMOOTHLY UP TO THIS POINT. I HAD BEEN ABLE TO CONTACT APCH ON THE GND FOR DEP FROM MY HOME FIELD (INSTEAD OF RELAYING THROUGH CLRNC DELIVERY), I WAS RELEASED IMMEDIATELY FOR DEP, AND APCH INDICATED THEY COULD ACCOMMODATE MY REQUESTS W/O MODIFICATION OR DELAYS. (ANY ONE OF THESE CONSTITUTES A MINOR MIRACLE!) I WAS LULLED INTO COMPLACENCY, EVERYTHING GOING PERFECTLY, HEADED FOR AN APCH THAT I HAD FLOWN DOZENS OF TIMES W/O PROBS. NONE OF THESE, HOWEVER, WERE SUFFICIENT GNDS FOR GIVING MY BRAIN THE REST OF THE DAY OFF, WHICH I OBVIOUSLY DID.

Data retrieved from NASA's ASRS site as of August 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.