Narrative:

I was flying as first officer from phx to ont and was the PF on this leg. ZLA gave us an assignment to descend and maintain 14000 ft. During the descent we were switched to ont approach and instructed to cross and intercept at 14000 ft, then descend and maintain 6000 ft. It is our normal procedure to allow the autoplt to capture any assigned altitude, and once this is accomplished move the altitude controller to the next assigned altitude. In this case the captain moved the controller to 6000 ft. Because of this, and also because I didn't interpret the clearance properly, I thought I was to cross an intersection at or below 14000 ft and maintain 6000 ft. I was nearing the intersection and would easily make the restr but elected to continue the descent down towards 6000 ft. I was then notified by approach control that I had descended below the altitude assigned to cross the fix. I feel that the problem arose primarily out of a breakdown in crew coordination and resource management. I also feel fatigue may have played a small roll in this occurrence. I would suggest that NASA and other safety organizations continue to stress the importance of cockpit resource management in multi-pilot aircraft.

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Original NASA ASRS Text

Title: ACR X NON ADHERENCE TO ATC CLRNC. ALTDEV OVERSHOOT OF XING RESTR.

Narrative: I WAS FLYING AS FO FROM PHX TO ONT AND WAS THE PF ON THIS LEG. ZLA GAVE US AN ASSIGNMENT TO DSND AND MAINTAIN 14000 FT. DURING THE DSCNT WE WERE SWITCHED TO ONT APCH AND INSTRUCTED TO CROSS AND INTERCEPT AT 14000 FT, THEN DSND AND MAINTAIN 6000 FT. IT IS OUR NORMAL PROC TO ALLOW THE AUTOPLT TO CAPTURE ANY ASSIGNED ALT, AND ONCE THIS IS ACCOMPLISHED MOVE THE ALT CTLR TO THE NEXT ASSIGNED ALT. IN THIS CASE THE CAPT MOVED THE CTLR TO 6000 FT. BECAUSE OF THIS, AND ALSO BECAUSE I DIDN'T INTERPRET THE CLRNC PROPERLY, I THOUGHT I WAS TO CROSS AN INTXN AT OR BELOW 14000 FT AND MAINTAIN 6000 FT. I WAS NEARING THE INTXN AND WOULD EASILY MAKE THE RESTR BUT ELECTED TO CONTINUE THE DSCNT DOWN TOWARDS 6000 FT. I WAS THEN NOTIFIED BY APCH CTL THAT I HAD DSNDED BELOW THE ALT ASSIGNED TO CROSS THE FIX. I FEEL THAT THE PROB AROSE PRIMARILY OUT OF A BREAKDOWN IN CREW COORD AND RESOURCE MGMNT. I ALSO FEEL FATIGUE MAY HAVE PLAYED A SMALL ROLL IN THIS OCCURRENCE. I WOULD SUGGEST THAT NASA AND OTHER SAFETY ORGANIZATIONS CONTINUE TO STRESS THE IMPORTANCE OF COCKPIT RESOURCE MGMNT IN MULTI-PLT ACFT.

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.