A GULFSTREAM IV EXPERIENCES AN ALT EXCURSION WHEN THE PIC FLYING AS FO INADVERTENTLY CAUSES A DISCONNECT OF THE AUTOPLT. THE ACFT CLBS TO 16900 FT BEFORE DSNDING TO THE ASSIGNED ALT OF 5000 FT.

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FO PF FROM L SEAT; TYPE RATED; BUT 50 HRS IN ACFT; WHEN ATC GAVE US A DSCNT TO 5000 FT FROM 15000 FT AND R TURN TO 250 DEGS; FOLLOWED BY FURTHER R TO 270 DEGS. THE FO PF SELECTED FLT LVL CHANGE ON THE GUIDANCE PANEL; AUTOTHROTTLES ON; AUTOPLT ON. THE THROTTLES WENT FORWARD INSTEAD OF BACK AND THE ACFT CLBED EVEN THOUGH 5000 FT HAD BEEN IMMEDIATELY SET BEFORE SELECTING FLT LVL CHANGE. THE ACFT CLBED TO 16900 FT BEFORE AUTOTHROTTLES AND AUTOPLT WERE DISCONNECTED. THE FO PF DID NOT RESPOND TO THE CAPT (PNF R SEAT) TO PULL THE PWR BACK. BUT NEITHER PLT NOTICED THE ALT EXCURSION UNTIL ATC SAID 'STATE YOUR ALT.' THE FO PF WAS BUSY SETTING HDG AND THE CAPT PNF BUSY LOOKING IN THE BOOK FOR A VREF SPD. THE FO WAS SURPRISED IN ACFT ACTION BUT IS SO NEW TO THE ACFT; WAS UNSURE OF WHAT TO DO AND SAID NOTHING. CONTRIBUTING FACTORS: MAINT INSTALLED 'EUROPEAN' DATABASE IN FMS'S INSTEAD OF THE 'WORLD.' THE FMS DID NOT RECOGNIZE BUT A COUPLE OF INTL ARPTS IN THE UNITED STATES OF AMERICA. THE FLT PLAN HAD BEEN DATA LINKED INTO THE FMS SO THE DEST WAS RECOGNIZED AS A WAYPOINT NOT AN ARPT. WE REALIZED THE PROB AFTER LEVELOFF WHEN I SELECTED IDENT ARPTS AND NO ARPTS CAME UP ACROSS THE UNITED STATES OF AMERICA. THE DATABASE DID NOT RECOGNIZE DEST ARPT; RWYS; STARS; APCHS. THE LNDG PERFORMANCE COULD NOT BE COMPUTED THROUGH THE LNDG INITIAL AND LNDG DATA IN THE FMS. THE CAPT PNF R SEAT WAS UNABLE TO ASSIST AND MONITOR THE NEW PF DURING A CRITICAL PHASE OF FLT BECAUSE HE WAS OVERLOADED MANUALLY CALCULATING VREF SPD AND MANUALLY ENTERING IT IN THE FMS (A JOB NOT NORMALLY REQUIRED IN A FULLY INTEGRATED COMPUTER FMS AIRPLANE); COMPLETING THE CHKLISTS; COMMUNICATING TO ATC ON THE RADIO; AND SETTING UP THE ILS COURSES AND FREQS ON BOTH SIDES. CORRECTIVE ACTIONS: MAINT WILL NO LONGER RECEIVE THE W AND E DATABASE; ONLY THE WORLD. I WILL NO LONGER GET SO INVOLVED IN OTHER THINGS SO I CAN FULLY ASSIST AND MONITOR THE OTHER PLT. I WILL CHK DATABASE CORRECTNESS BEFORE FLT BUT WITH 2 HRS REQUIRED TO INPUT DATABASE I WON'T HAVE TIME TO CHANGE IT BUT WILL BE BETTER PREPARED TO HANDLE IT APPROPRIATELY. SUPPLEMENTAL INFO FROM ACN 419280: ACFT HIGH; CLOSE IN; BECAUSE CAPT (PNF) FAILED TO SWITCH TO NEXT CTLR. HE WAS OVERLOADED TRYING TO FIND LNDG DATA; WORK RADIOS AND LOAD FMS. THERE WAS A LOT OF DISTR GENERATED BY THIS PROCESS. PF MAKES HDG CHANGES WHILE TRYING TO GET PROGRESS FROM PNF. PF FAILS TO SEE THAT ACFT IS CLBING INSTEAD OF DSNDING AS COMMANDED ON AUTOPLT. SIMULTANEOUSLY DISCOVERED BY CREW MEMBERS AND ATC. ATC ASKS FOR ALT RPT. CAPT (PNF) RPTS DSNDING THROUGH 16000 FT FOR 5000 FT. FO (PF) DISCONNECTED AUTOPLT AND AUTOTHROTTLES AND IMMEDIATELY BEGAN DSCNT TO ASSIGNED ALT OF 5000 FT. AUTOPLT WAS RE-ENGAGED AT 5000 FT WITH NO FURTHER ABNORMALITIES OBSERVED. CHIEF PLT NOTIFIED UPON LNDG. MEETING FOLLOWED RESULTING IN FOLLOWING: 1) DATABASE IS NOW A MAINT AND PLT SIGNOFF ON PREFLT RELEASE. 2) PLTS WILL MAKE THIS OCCURRENCE A SAFETY PRESENTATION TO ENTIRE FLT DEPT. 3) AUTOPLT GLITCH RPTED TO MAINT. IT WAS ORIGINALLY BELIEVED BY THE CREW THAT THE AUTOPLT HAD CLBED THE ACFT WHEN COMMANDED BY FLC TO DSND. IN THE IN-HOUSE EXAMINATION OF THE EVENT; IT HAS BEEN DISCOVERED THAT THE FO MADE THE CORRECT INPUTS TO THE AUTOPLT TO DSND FROM 15000 FT TO 5000 FT AS DIRECTED BY ATC. THE AUTOPLT WAS WORKING CORRECTLY AFTER ALL. IT IS NOW KNOWN THAT THE CAPT (PNF); WITH APPROX 5 YRS IN THIS ACFT; MOVED THE ELECTRIC TRIM SWITCH WHEN HE MEANT TO MOVE THE MIKE SWITCH; WHICH IS NEXT TO IT. THIS DISCONNECTED THE AUTOPLT. THE CREW MISSED THE AURAL WARNING BECAUSE OF MULTIPLE DISTRS IN THE COCKPIT. WHILE THIS DOES NOT ABSOLVE THE CREW; IT DOES SHOW THE DANGER OF HAVING THE PITCH SWITCH AND MIKE SWITCH NEXT TO EACH OTHER. ALL PLTS IN THE DEPT STATED THAT THEY HAVE INADVERTENTLY HIT THE PITCH INSTEAD OF MIKE; BUT WITHOUT DISTRS; HEARD THE AURAL WARNING AND SIMPLY RESELECTED THE AUTOPLT ON. WE AS A VERY SAFETY ORIENTED FLT DEPT FEEL THAT PUTTING THESE SWITCHES NEXT TO EACH OTHER IS A VERY UNSAFE DESIGN AND COULD EASILY CONTRIBUTE TO AN ACCIDENT.