Narrative:

Have you ever looked at something and what you saw was completely different than what was actually there? This is the only way I can describe what happened to our flight. I had noted to myself at our flight planning earlier what a low altimeter setting it was for sfo this day (29.42). Actually, the altimeter was 30.42 and I either misread it, glanced over it or just plain didn't register it. In any event, I remembered 29.42 instead of the reported actual 30.42 pressure at sfo, our takeoff airport. Climbing through FL180, I had a chance to catch the mental mistake when I went to reset my altimeter to 29.92. It must be noted that at this point my altimeter was set properly to 30.42. However, thinking 29.42 and I must confess only looking at the .42 part of the kohlsman window, I naturally turned the setting 'up' to 29.92 from my preconceived 29.42. What I actually did of course was to set 30.92 in my altimeter causing us to be 1000 ft off of our assigned altitude of FL330 at leveloff. Obviously, I had many clues as to my error, but for whatever reason, none registered until ATC asked our altitude and then gave us a descent to a lower altitude. I don't believe there were any conflicts with other traffic and for whatever reason the first officer and possibly the controller did not catch my mistake either. As we approached FL240, the first officer called for me to level off, but I thought we had 1000 ft to go. The confusion led to the discovery of my misset altimeter. We leveled properly and reset my altimeter properly. I cannot explain why all these lapses occurred as the first officer and I are usually very careful to follow SOP and stay aware situationally, but it did.

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Original NASA ASRS Text

Title: FLC OF B737 SET ALTIMETER PASSING THROUGH FL180 ERRONEOUSLY RESULTING IN 1000 FT DIFFERENCE FROM ASSIGNED ALT.

Narrative: HAVE YOU EVER LOOKED AT SOMETHING AND WHAT YOU SAW WAS COMPLETELY DIFFERENT THAN WHAT WAS ACTUALLY THERE? THIS IS THE ONLY WAY I CAN DESCRIBE WHAT HAPPENED TO OUR FLT. I HAD NOTED TO MYSELF AT OUR FLT PLANNING EARLIER WHAT A LOW ALTIMETER SETTING IT WAS FOR SFO THIS DAY (29.42). ACTUALLY, THE ALTIMETER WAS 30.42 AND I EITHER MISREAD IT, GLANCED OVER IT OR JUST PLAIN DIDN'T REGISTER IT. IN ANY EVENT, I REMEMBERED 29.42 INSTEAD OF THE RPTED ACTUAL 30.42 PRESSURE AT SFO, OUR TKOF ARPT. CLBING THROUGH FL180, I HAD A CHANCE TO CATCH THE MENTAL MISTAKE WHEN I WENT TO RESET MY ALTIMETER TO 29.92. IT MUST BE NOTED THAT AT THIS POINT MY ALTIMETER WAS SET PROPERLY TO 30.42. HOWEVER, THINKING 29.42 AND I MUST CONFESS ONLY LOOKING AT THE .42 PART OF THE KOHLSMAN WINDOW, I NATURALLY TURNED THE SETTING 'UP' TO 29.92 FROM MY PRECONCEIVED 29.42. WHAT I ACTUALLY DID OF COURSE WAS TO SET 30.92 IN MY ALTIMETER CAUSING US TO BE 1000 FT OFF OF OUR ASSIGNED ALT OF FL330 AT LEVELOFF. OBVIOUSLY, I HAD MANY CLUES AS TO MY ERROR, BUT FOR WHATEVER REASON, NONE REGISTERED UNTIL ATC ASKED OUR ALT AND THEN GAVE US A DSCNT TO A LOWER ALT. I DON'T BELIEVE THERE WERE ANY CONFLICTS WITH OTHER TFC AND FOR WHATEVER REASON THE FO AND POSSIBLY THE CTLR DID NOT CATCH MY MISTAKE EITHER. AS WE APCHED FL240, THE FO CALLED FOR ME TO LEVEL OFF, BUT I THOUGHT WE HAD 1000 FT TO GO. THE CONFUSION LED TO THE DISCOVERY OF MY MISSET ALTIMETER. WE LEVELED PROPERLY AND RESET MY ALTIMETER PROPERLY. I CANNOT EXPLAIN WHY ALL THESE LAPSES OCCURRED AS THE FO AND I ARE USUALLY VERY CAREFUL TO FOLLOW SOP AND STAY AWARE SITUATIONALLY, BUT IT DID.

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.