Temporary loss of aircraft control in an air carrier widebody transport as the #1 INS fails.

Attributes
ACN	307323
Time
Date	199506
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : zme
State Reference	TN
Altitude	msl bound lower : 35000 msl bound upper : 35400
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zme
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
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 : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 165 flight time total : 17400 flight time type : 2000
ASRS Report	307323
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude other anomaly other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : regained aircraft control flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

In cruise with the #1 autoplt engaged, the #1 INS (which provides the inputs to the #1 autoplt) tumbled. The autoplt, following the #1 INS commands, abruptly rolled the aircraft 30 degrees to the right and slightly nose down. My ADI was rolling and I had numerous red flags. My first reaction was to try to overpwr the autoplt manually. The first officer disconnected the autoplt. I rolled wings level and in the process climbed 400 ft above assigned altitudes. I then gave the first officer aircraft to fly back to assigned altitude. Advised ATC of INS failure and that we had climbed 400 ft. They weren't concerned. We continued to destination without incident using #2 autoplt and first officer flying as my ADI and HSI were inoperative. I would like to make a couple comments. Although this was a non event, another second on the autoplt and in IMC or darkness and momentary pilot disorientation could easily result in an unusual altitude with serious consequences. All 3 of us in the cockpit had the same thought. Could this have caused the accident in pittsburgh? If the autoplt was engaged, I would bet even odds that the autoplt and not the INS was the cause.

Original NASA ASRS Text

Title: TEMPORARY LOSS OF ACFT CTL IN AN ACR WDB AS THE #1 INS FAILS.

Narrative: IN CRUISE WITH THE #1 AUTOPLT ENGAGED, THE #1 INS (WHICH PROVIDES THE INPUTS TO THE #1 AUTOPLT) TUMBLED. THE AUTOPLT, FOLLOWING THE #1 INS COMMANDS, ABRUPTLY ROLLED THE ACFT 30 DEGS TO THE R AND SLIGHTLY NOSE DOWN. MY ADI WAS ROLLING AND I HAD NUMEROUS RED FLAGS. MY FIRST REACTION WAS TO TRY TO OVERPWR THE AUTOPLT MANUALLY. THE FO DISCONNECTED THE AUTOPLT. I ROLLED WINGS LEVEL AND IN THE PROCESS CLBED 400 FT ABOVE ASSIGNED ALTS. I THEN GAVE THE FO ACFT TO FLY BACK TO ASSIGNED ALT. ADVISED ATC OF INS FAILURE AND THAT WE HAD CLBED 400 FT. THEY WEREN'T CONCERNED. WE CONTINUED TO DEST WITHOUT INCIDENT USING #2 AUTOPLT AND FO FLYING AS MY ADI AND HSI WERE INOP. I WOULD LIKE TO MAKE A COUPLE COMMENTS. ALTHOUGH THIS WAS A NON EVENT, ANOTHER SECOND ON THE AUTOPLT AND IN IMC OR DARKNESS AND MOMENTARY PLT DISORIENTATION COULD EASILY RESULT IN AN UNUSUAL ALT WITH SERIOUS CONSEQUENCES. ALL 3 OF US IN THE COCKPIT HAD THE SAME THOUGHT. COULD THIS HAVE CAUSED THE ACCIDENT IN PITTSBURGH? IF THE AUTOPLT WAS ENGAGED, I WOULD BET EVEN ODDS THAT THE AUTOPLT AND NOT THE INS WAS THE CAUSE.

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.