Narrative:

While in straight and level cruise at FL330 we experienced a failure of the #2 INS causing the aircraft to pitch up and turn right. The pitch and turn were not violent, but fairly firm. As a result, we gained about 600 ft and turned right approximately 60 degrees by the time we were confident the problem was under control. Canadian ATC called to tell us we were about 10 mi north of track and headed north. We knew that, but were a little busy trying to analyze the problem to give a full report till a few mins later. Details: B747F ord to anc, clear night, no moon, few visual references to horizon, using INS navigation, using 'B' autoplt, copilot flying, pms engaged. Approaching ft smith, level at FL330, aircraft began an abrupt right climbing turn. Autoplt was disengaged and aircraft returned to straight and level flight. Indications and warnings: got gyro flag and computer flag on #2 ADI. #2 ADI frozen at 10 degree pitch up and 20 degree right bank. Red warning flags on first officer RMI and HSI. Red and amber warnings on both first officer and captain instrument warning system. 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 communication, we switched the copilot's instruments to the #3 INS and then shut down #2 INS. Remainder of flight normal. Comment: back of clock flying, fatigue, multitude of aural and visual warnings and poor visual horizon outside aircraft delayed confidence in what we were seeing for several seconds. This also prevented an immediate call to canadian ATC to report our problem. Later radio calls to ATC explained problem to their satisfaction. Solution: stuff happens, we must always be aware of possible dramatic instrument or equipment failures.

Related reports:

Google
 

Original NASA ASRS Text

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

Narrative: 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.

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.