AN ACR A310 CLBED THROUGH THE MISSED APCH ALT.

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AT ABOUT 2000 FT ON ILS APCH; WE EXPERIENCED AN UNSCHEDULED PITCH TRIM EVENT; WHICH RESULTED IN A PITCH UP ALT OF MORE THAN 20 DEGS WITH AUTO THROTTLES GOING TO GAR THRUST. BY THE TIME WE RECOVERED; WE WERE AT 4000 FT; BUT MISSED APCH ALT WAS 3000 FT. I DO NOT KNOW IF THERE WERE ANY TFC CONFLICTS. THIS WAS THE SECOND LEG OF A TRANSOCEANIC TRIP AND WE WERE ALL TIRED. THE TRIM IS SUPPOSED TO GIVE AN AURAL WARNING IF IT RUNS AWAY OR IF USED FOR MORE THAN 1 SECOND. NO ONE HEARD THIS; BUT WE SAW THE THROTTLES ADVANCING; WHICH CONTRIBUTED TO BOTH PITCH UP AND MOMENTARY CONFUSION ABOUT WHAT CAUSED THE PITCH UP. WE BELIEVE IT WAS CAUSED A STICKING TRIM SWITCH BUT ARE NOT SURE. MAINT FOUND NOTHING WRONG. PERHAPS THE ADDITION OF A WARNING LIGHT IN ADDITION TO THE AURAL WARNING (WHICH IS HARD TO HEAR ABOVE AMBIENT COCKPIT NOISE AND RADIO XMISSIONS) WOULD HAVE HELPED US TO RECOGNIZE THE SOURCE OF THE PROB MORE PROMPTLY WHEN VERY TIRED. AFTER AN ALL NIGHT OCEAN XING WE ALL NEED ALL THE HELP WE CAN GET. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR WAS FLYING AN AIRBUS A 310 FOR A U.S. BASED ACR. THE ACFT WAS BEING FLOWN MANUALLY BY THE FO WITH AUTO THROTTLE ENGAGED. THE AUTO THROTTLES WENT TWICE TO 'FULL HERMAN' FOR NO APPARENT REASON AND THE ELEVATOR TRIM WAS BEING DRIVEN TOWARDS FULL NOSE UP WITH NO COMMAND FROM EITHER PLT. THE RPTING CAPT RETARDED THE THROTTLES TWICE; THEN HIT HIS TRIM SWITCH FORWARD TO NOSE DOWN. AS THE ENGS ARE SLUNG UNDER THE WINGS; THE NOSE UP PITCH WAS ACCENTUATED BY THE ABRUPT THROTTLE MOVEMENT. ACR MAINT AT CPH WAS UNABLE TO FIND ANY PROB. ACR MAINT AT THE CREW'S HOME BASE CHANGED THE FO'S TRIM SWITCH THINKING THAT IT MIGHT HAVE MOMENTARILY STUCK IN THE NOSE UP POS. THE RPTR KNOWS OF NO OTHER INCIDENTS OF THIS TYPE; BUT THERE HAVE BEEN UNWANTED NOSE UP PITCHES WHEN THIS TYPE ACFT HAS BEEN MAKING A COUPLED APCH. THE CREW HAD NO FURTHER PROB CTLLING THE ACFT ON THE NEXT APCH AND LNDG.