G4 CORP FLC SETS CLB SPD RATE INSTEAD OF DSND SPD RATE IN VERT SPD MODE SELECTOR.

Narrative

WE WERE ON OUR LAST LEG OF THE DAY; FROM SAN FRANCISCO TO SAN DIEGO; CA; LEVEL AT FL410. AUTOPLT AND AUTOTHROTTLES ENGAGED. WX WAS CLR AND IT WAS DUSK SO WE WERE GOING THROUGH THE PROCESS OF ADJUSTING THE COCKPIT LIGHTS AS THE CONDITIONS GOT DARKER. APCHING LAX VOR AND THE FO LEFT HIS SEAT WHILE LOOKING FOR A MISSING APCH PLATE. WHILE THE FO WAS OUT OF HIS SEAT ZLA CLRED US FROM FL410 TO FL330. I REACHED OVER AND SET THE ALT SELECT TO 33000 FT; THEN SELECTED VERT SPD AND DIALED 2500 FT RATE THEN SELECTED AUTO LAND ON THE PRESSURIZATION PANEL. AS I FINISHED INITIATING THE DSCNT THE FO RETURNED TO HIS SEAT AND VERBALLY CONFIRMED THE FLT LEVEL CLRNC CHANGE. THE FO WAS STILL LOOKING FOR THE ARPT DIAGRAM. APPROX A MIN LATER WE GOT A CABIN DIFFERENTIAL -9.6 (AMBER) WARNING ON THE CAS. THE PRESSURIZATION TRANSDUCER HAD BEEN REPLACED PRIOR TO OUR TRIP DUE TO A PREVIOUS PRESSURIZATION PROB SO; OUR INITIAL THOUGHT WAS; WHAT'S WRONG NOW WITH THE PRESSURIZATION? WE QUICKLY DISCOVERED THAT THE ONLY PROB WAS THAT WE REALLY HAD 9.6 PSI CABIN DIFFERENTIAL; 9.4 BEING NORMAL. I LOOKED AT THE ALTIMETER AND WE WERE CLBING THROUGH FL430! NOT KNOWING WHY WE WERE CLBING AT THAT INSTANT I DISCONNECTED THE AUTOPLT AND AUTOTHROTTLES AND STARTED AN IMMEDIATE DSCNT TOWARD FL330. (THE PEAK ALT I SAW WAS 43400 FT.) A RATE OF AROUND 4000 FPM WAS ESTABLISHED THEN CHKED THE TCASII AND SAW NO OTHER TFC. BY THE TIME WE ESTABLISHED THE DSCNT; CHKED TCASII A NUMBER OF TIMES AND WERE MENTALLY EVALUATING WHAT COULD HAVE HAPPENED WE WERE GOING THROUGH FL410; SO NOTHING WAS SAID TO ATC. I HAD SET IN A RATE OF 2500 FT IN THE VERT SPD MODE SELECTOR INSTEAD OF -2500 FT. I REMEMBER SEEING THE ALT AND VERT SPD TAPES MOVE AFTER I INITIATED THE ALT CHANGE BUT; OBVIOUSLY DIDN'T READ AT THE DIGITS. CONTRIBUTING FACTORS: NUISANCE OF HAVING TO ADJUST THE COCKPIT LIGHTING EVERY SO OFTEN DURING DUSK. CAPT PERFORMING THE FO DUTIES WHILE THE FO WAS LOOKING FOR THE ARPT DIAGRAM PLATE. ALREADY A 12 HR DUTY DAY WITH A 3 HR TIME ZONE CHANGE THE PREVIOUS NIGHT. HAD BEEN AWAKE SINCE 3 AM PDST. ALTHOUGH I HAVE BEEN FLYING TAPE DISPLAY FLT INST FOR ABOUT 9 HRS; I PROBABLY WOULD HAVE PICKED UP THE ERROR WITH ROUND NEEDLE DISPLAYS IMMEDIATELY. FROM NOW ON I WILL VERIFY THAT THE COMMAND WE INTENDED WITH THE AUTO FLT SYS IS WHAT THE ACFT IS ACTUALLY DOING.