Narrative:

WX at the destination had changed rapidly in the last hour. Reported WX was below minimums for the approach as reported by ATIS. I decided to shoot the approach anyway for practice and to confirm the WX was as reported (-X 1/16 F). Runway environment was not in sight at decision ht and the missed approach was initiated. After the climb was started and turn to the west initiated, I glanced down at my knee board to confirm the cleared altitude as 2000 ft. I also started to think about how I was going to contact the people that expected to meet me at tacoma narrows airport. When I looked up I read the altimeter as passing through 2000 and stopped my climb and descended to what I thought was my cleared altitude. I had also switched from tower frequency during this time and checked in with departure as level at 2000 ft. They quickly replied with 'confirm level 2000 ft' and then reported an altitude alert and a command to 'climb immediately to 2000 ft.' at this time I again looked at the altimeter and realized that I was actually level at 1000 ft. Climb to 2000 ft was uneventful and the flight continued to the alternate airfield (bfi). How did it happen: pilot distracted from flying and scanning instruments to confirm missed approach altitude and by concern about contacting people waiting for the pilot at the destination. Altimeter is classic clock style without a numerical drum readout. I understand now why many people have misread this type of altimeter in the past. Cloud tops at the OM were about 2000 ft. Tops over the airport were just below 1000 ft. When I broke out on top after the missed approach, I assumed I must be about 2000 ft. In fact I thought to myself, better check your altitude. My mind expected to see 2000 ft and when I saw the big hand passing through 12 O'clock I thought I was passing my assigned altitude.

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Original NASA ASRS Text

Title: ALTDEV ALT UNDERSHOT IN MISSED APCH PROC.

Narrative: WX AT THE DEST HAD CHANGED RAPIDLY IN THE LAST HR. RPTED WX WAS BELOW MINIMUMS FOR THE APCH AS RPTED BY ATIS. I DECIDED TO SHOOT THE APCH ANYWAY FOR PRACTICE AND TO CONFIRM THE WX WAS AS RPTED (-X 1/16 F). RWY ENVIRONMENT WAS NOT IN SIGHT AT DECISION HT AND THE MISSED APCH WAS INITIATED. AFTER THE CLB WAS STARTED AND TURN TO THE W INITIATED, I GLANCED DOWN AT MY KNEE BOARD TO CONFIRM THE CLRED ALT AS 2000 FT. I ALSO STARTED TO THINK ABOUT HOW I WAS GOING TO CONTACT THE PEOPLE THAT EXPECTED TO MEET ME AT TACOMA NARROWS ARPT. WHEN I LOOKED UP I READ THE ALTIMETER AS PASSING THROUGH 2000 AND STOPPED MY CLB AND DSNDED TO WHAT I THOUGHT WAS MY CLRED ALT. I HAD ALSO SWITCHED FROM TWR FREQ DURING THIS TIME AND CHKED IN WITH DEP AS LEVEL AT 2000 FT. THEY QUICKLY REPLIED WITH 'CONFIRM LEVEL 2000 FT' AND THEN RPTED AN ALT ALERT AND A COMMAND TO 'CLB IMMEDIATELY TO 2000 FT.' AT THIS TIME I AGAIN LOOKED AT THE ALTIMETER AND REALIZED THAT I WAS ACTUALLY LEVEL AT 1000 FT. CLB TO 2000 FT WAS UNEVENTFUL AND THE FLT CONTINUED TO THE ALTERNATE AIRFIELD (BFI). HOW DID IT HAPPEN: PLT DISTRACTED FROM FLYING AND SCANNING INSTS TO CONFIRM MISSED APCH ALT AND BY CONCERN ABOUT CONTACTING PEOPLE WAITING FOR THE PLT AT THE DEST. ALTIMETER IS CLASSIC CLOCK STYLE WITHOUT A NUMERICAL DRUM READOUT. I UNDERSTAND NOW WHY MANY PEOPLE HAVE MISREAD THIS TYPE OF ALTIMETER IN THE PAST. CLOUD TOPS AT THE OM WERE ABOUT 2000 FT. TOPS OVER THE ARPT WERE JUST BELOW 1000 FT. WHEN I BROKE OUT ON TOP AFTER THE MISSED APCH, I ASSUMED I MUST BE ABOUT 2000 FT. IN FACT I THOUGHT TO MYSELF, BETTER CHK YOUR ALT. MY MIND EXPECTED TO SEE 2000 FT AND WHEN I SAW THE BIG HAND PASSING THROUGH 12 O'CLOCK I THOUGHT I WAS PASSING MY ASSIGNED ALT.

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.