An air carrier B747-200A suffered an INS gyro failure.

Attributes
ACN	337283
Time
Date	199605
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : fue
State Reference	FO
Altitude	msl bound lower : 29000 msl bound upper : 29800
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : rjtg
Operator	common carrier : air carrier
Make Model Name	B747-100
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : second officer instruction : instructor
Qualification	pilot : atp pilot : commercial pilot : flight engineer pilot : instrument pilot : cfi
Experience	flight time last 90 days : 180 flight time total : 11000 flight time type : 4000
ASRS Report	337283
Person 2
Affiliation	company : air carrier
Function	flight crew : second officer
Qualification	pilot : flight engineer
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : regained aircraft control flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

We had a gyro failure of #1 INS. Autoplt tried to follow ADI in climbing left turn at FL290. First officer was in lavatory. I was instructing so student from jump seat. I jumped into first officer seat and flew aircraft back down from FL298 to FL290. 800 ft vertical climb without clearance due to gyro failure. Captain's instruments were all spinning out of control. It only took about 20 seconds to correct the 800 ft altitude deviation. It was a surprise to see how fast aircraft climbed and how many seconds it took for myself and captain to sort out which instruments were bad and to correct the situation. When gyro went, autoplt disconnected, but autothrottles stayed engaged and added power when the autoplt tried to follow failed ADI in climbing left turn. It was a moderately violent pitch up at onset. Recommendations -- not for altitude bust but for recognition: keep your eyes open, guys. We were glad that traffic had kept us down to FL290. At FL350 or FL370 we might have stalled with the 1.5 G initial pitch up!

Original NASA ASRS Text

Title: AN ACR B747-200A SUFFERED AN INS GYRO FAILURE.

Narrative: WE HAD A GYRO FAILURE OF #1 INS. AUTOPLT TRIED TO FOLLOW ADI IN CLBING L TURN AT FL290. FO WAS IN LAVATORY. I WAS INSTRUCTING SO STUDENT FROM JUMP SEAT. I JUMPED INTO FO SEAT AND FLEW ACFT BACK DOWN FROM FL298 TO FL290. 800 FT VERT CLB WITHOUT CLRNC DUE TO GYRO FAILURE. CAPT'S INSTS WERE ALL SPINNING OUT OF CTL. IT ONLY TOOK ABOUT 20 SECONDS TO CORRECT THE 800 FT ALTDEV. IT WAS A SURPRISE TO SEE HOW FAST ACFT CLBED AND HOW MANY SECONDS IT TOOK FOR MYSELF AND CAPT TO SORT OUT WHICH INSTS WERE BAD AND TO CORRECT THE SIT. WHEN GYRO WENT, AUTOPLT DISCONNECTED, BUT AUTOTHROTTLES STAYED ENGAGED AND ADDED PWR WHEN THE AUTOPLT TRIED TO FOLLOW FAILED ADI IN CLBING L TURN. IT WAS A MODERATELY VIOLENT PITCH UP AT ONSET. RECOMMENDATIONS -- NOT FOR ALT BUST BUT FOR RECOGNITION: KEEP YOUR EYES OPEN, GUYS. WE WERE GLAD THAT TFC HAD KEPT US DOWN TO FL290. AT FL350 OR FL370 WE MIGHT HAVE STALLED WITH THE 1.5 G INITIAL PITCH UP!

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.