ACFT EQUIP PROB. #2 INS FAILURE. AUTOPLT PITCHED UP AND TURNED R CAUSING ALT AND HDG DEV.

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WHILE IN STRAIGHT AND LEVEL CRUISE AT FL330 WE EXPERIENCED A FAILURE OF THE #2 INS CAUSING THE ACFT TO PITCH UP AND TURN R. THE PITCH AND TURN WERE NOT VIOLENT; BUT FAIRLY FIRM. AS A RESULT; WE GAINED ABOUT 600 FT AND TURNED R APPROX 60 DEGS BY THE TIME WE WERE CONFIDENT THE PROB WAS UNDER CTL. CANADIAN ATC CALLED TO TELL US WE WERE ABOUT 10 MI N OF TRACK AND HEADED N. WE KNEW THAT; BUT WERE A LITTLE BUSY TRYING TO ANALYZE THE PROB TO GIVE A FULL RPT TILL A FEW MINS LATER. DETAILS: B747F ORD TO ANC; CLR NIGHT; NO MOON; FEW VISUAL REFS TO HORIZON; USING INS NAV; USING 'B' AUTOPLT; COPLT FLYING; PMS ENGAGED. APCHING FT SMITH; LEVEL AT FL330; ACFT BEGAN AN ABRUPT R CLBING TURN. AUTOPLT WAS DISENGAGED AND ACFT RETURNED TO STRAIGHT AND LEVEL FLT. INDICATIONS AND WARNINGS: GOT GYRO FLAG AND COMPUTER FLAG ON #2 ADI. #2 ADI FROZEN AT 10 DEG PITCH UP AND 20 DEG R BANK. RED WARNING FLAGS ON FO RMI AND HSI. RED AND AMBER WARNINGS ON BOTH FO AND CAPT INST WARNING SYS. AUTOPLT WAILER AND RED AUTOTHROTTLE DISENGAGE LIGHTS. #2 INS RED WARN LIGHT ON CDU. WE DETERMINED THAT THE #2 INS GYRO PLATFORM HAD FAILED. THE AUTOPLT PROBABLY TRIED TO CORRECT USING ERRONEOUS PITCH AND ROLL DATA. USING OUR SOP AND COM; WE SWITCHED THE COPLT'S INSTRUMENTS TO THE #3 INS AND THEN SHUT DOWN #2 INS. REMAINDER OF FLT NORMAL. COMMENT: BACK OF CLOCK FLYING; FATIGUE; MULTITUDE OF AURAL AND VISUAL WARNINGS AND POOR VISUAL HORIZON OUTSIDE ACFT DELAYED CONFIDENCE IN WHAT WE WERE SEEING FOR SEVERAL SECONDS. THIS ALSO PREVENTED AN IMMEDIATE CALL TO CANADIAN ATC TO RPT OUR PROB. LATER RADIO CALLS TO ATC EXPLAINED PROB TO THEIR SATISFACTION. SOLUTION: STUFF HAPPENS; WE MUST ALWAYS BE AWARE OF POSSIBLE DRAMATIC INST OR EQUIP FAILURES.