A widebody transport air carrier crew had an apparent navigation anomaly between their inertial reference units and their flight management computers.

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Attributes
ACN	209992
Time
Date	199205
Day	Fri
Local Time Of Day	0001 To 0600
Place
Locale Reference	atc facility : cdb
State Reference	AK
Altitude	msl bound lower : 37000 msl bound upper : 37000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zoa
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 3 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute : other oceanic enroute : pacific enroute 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 : 30 flight time total : 25000 flight time type : 130
ASRS Report	209992
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe other anomaly other other spatial deviation
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : became reoriented flight crew : overcame equipment problem flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation other

Narrative:

From rjaa to klax while post position plot, first officer 'froze' position 'update' prompt with a 'snowflake' appeared and was inserted 'check position' appeared on the navigation display FMC 1 and 2. We concluded that the IRU's were od and FMC's were off. We updated the FMC's to the IRU's. Everything now appeared normal. We informed hnl of possible unreliable navigation.

Original NASA ASRS Text

Title: A WDB ACR CREW HAD AN APPARENT NAV ANOMALY BTWN THEIR INERTIAL REF UNITS AND THEIR FLT MGMNT COMPUTERS.

Narrative: FROM RJAA TO KLAX WHILE POST POS PLOT, FO 'FROZE' POS 'UPDATE' PROMPT WITH A 'SNOWFLAKE' APPEARED AND WAS INSERTED 'CHK POS' APPEARED ON THE NAV DISPLAY FMC 1 AND 2. WE CONCLUDED THAT THE IRU'S WERE OD AND FMC'S WERE OFF. WE UPDATED THE FMC'S TO THE IRU'S. EVERYTHING NOW APPEARED NORMAL. WE INFORMED HNL OF POSSIBLE UNRELIABLE NAV.

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.