Narrative:

On descent to sfo, I descended below 6000' toward 4000', incorrectly believing that I was cleared to 4000' for the quiet bridge visibility approach to sfo. This was the second leg of a 2 leg trip during which a reserve captain, acting as copilot, had not only been continually complaining with a great deal of acrimony about having to act as copilot, but was positively distracting from the operation by his failure to perform his copilot duties--and by questioning my every move and making decisions that were often contrary to my wishes and communicating his decisions to ATC. The altitude bust was, however, entirely my fault. Bay approach had asked if we had sfo in sight. I said yes to my copilot, and he replied with words to the effect expressing his disapproval. I somehow at this time got the impression that we were in fact cleared for the quiet bridge visibility approach, which would allow a descent to 4000' at menlo. I therefore left 6000' and started a descent. Bay approach brought my attention to the error at about 5500'. I was then able to prevail upon my copilot to acknowledge that the field was in sight, and we were then cleared for a visibility approach. I think that in the future I will have to take into account my fellow crew member's willingness to perform west/O reservation. I am sure that he is probably a very good captain, but his feelings of having been put upon by being assigned to a position beneath his usual status, and his unfamiliarity with his temporary position made for a total lack of crew coordination. This occurrence also gave me some insight into my own limitations.

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Original NASA ASRS Text

Title: ACR WDB ALT DEVIATION EXCURSION FROM CLRNC ALT ON VISUAL APCH TO SFO.

Narrative: ON DSCNT TO SFO, I DSNDED BELOW 6000' TOWARD 4000', INCORRECTLY BELIEVING THAT I WAS CLRED TO 4000' FOR THE QUIET BRIDGE VIS APCH TO SFO. THIS WAS THE SECOND LEG OF A 2 LEG TRIP DURING WHICH A RESERVE CAPT, ACTING AS COPLT, HAD NOT ONLY BEEN CONTINUALLY COMPLAINING WITH A GREAT DEAL OF ACRIMONY ABOUT HAVING TO ACT AS COPLT, BUT WAS POSITIVELY DISTRACTING FROM THE OPERATION BY HIS FAILURE TO PERFORM HIS COPLT DUTIES--AND BY QUESTIONING MY EVERY MOVE AND MAKING DECISIONS THAT WERE OFTEN CONTRARY TO MY WISHES AND COMMUNICATING HIS DECISIONS TO ATC. THE ALT BUST WAS, HOWEVER, ENTIRELY MY FAULT. BAY APCH HAD ASKED IF WE HAD SFO IN SIGHT. I SAID YES TO MY COPLT, AND HE REPLIED WITH WORDS TO THE EFFECT EXPRESSING HIS DISAPPROVAL. I SOMEHOW AT THIS TIME GOT THE IMPRESSION THAT WE WERE IN FACT CLRED FOR THE QUIET BRIDGE VIS APCH, WHICH WOULD ALLOW A DSCNT TO 4000' AT MENLO. I THEREFORE LEFT 6000' AND STARTED A DSCNT. BAY APCH BROUGHT MY ATTN TO THE ERROR AT ABOUT 5500'. I WAS THEN ABLE TO PREVAIL UPON MY COPLT TO ACKNOWLEDGE THAT THE FIELD WAS IN SIGHT, AND WE WERE THEN CLRED FOR A VIS APCH. I THINK THAT IN THE FUTURE I WILL HAVE TO TAKE INTO ACCOUNT MY FELLOW CREW MEMBER'S WILLINGNESS TO PERFORM W/O RESERVATION. I AM SURE THAT HE IS PROBABLY A VERY GOOD CAPT, BUT HIS FEELINGS OF HAVING BEEN PUT UPON BY BEING ASSIGNED TO A POS BENEATH HIS USUAL STATUS, AND HIS UNFAMILIARITY WITH HIS TEMPORARY POS MADE FOR A TOTAL LACK OF CREW COORD. THIS OCCURRENCE ALSO GAVE ME SOME INSIGHT INTO MY OWN LIMITATIONS.

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.