B747 captain reports left FMC failure and restart over north pacific.

Attributes
ACN	791143
Time
Date	200806
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : zoa.artcc
State Reference	CA
Altitude	msl single value : 34000
Aircraft 1
Controlling Facilities	artcc : zoa.artcc
Operator	common carrier : air carrier
Make Model Name	B747-400
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Route In Use	enroute : pacific
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 300 flight time total : 25000 flight time type : 2100
ASRS Report	791143
Events
Anomaly	aircraft equipment problem : less severe other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	aircraft : equipment problem dissipated flight crew : overcame equipment problem
Consequence	other
Supplementary
Problem Areas	Aircraft Maintenance Human Performance
Primary Problem	Aircraft

Narrative:

While attempting to perform a route modification on the left CDU; the CDU locked up then went blank; appeared to lose power. Time was XA45; position was about 1/2 way between W140 and W150. Then lost autothrottles; lav and VNAV. Captain assumed manual control of aircraft. Did not have EICAS message indicating 'FMC left' at this time but captain ordered first officer to select the FMC master selector switch to select the right FMC in an attempt to restore navigation. Autoplt was reengaged in altitude and heading select. About 4 mins after left CDU lost power; power returned. Left CDU had lost all stored data and right CDU had lost some stored data. Reinserted data; selected active waypoint; autothrottle; LNAV and VNAV. Reviewed irregular procedure 'FMC left.' performed position plot to verify position at XB01Z. Contacted san francisco oceanic on HF to explain the loss of LNAV. Operator advised loss of cpdlc connection. Reinserted data and sent position report. Contacted dispatch and maintenance on satcom. Pointed out the previous history of left CDU. Continued flight. Briefed maintenance on arrival.

Original NASA ASRS Text

Title: B747 CAPT REPORTS LEFT FMC FAILURE AND RESTART OVER NORTH PACIFIC.

Narrative: WHILE ATTEMPTING TO PERFORM A RTE MODIFICATION ON THE L CDU; THE CDU LOCKED UP THEN WENT BLANK; APPEARED TO LOSE PWR. TIME WAS XA45; POS WAS ABOUT 1/2 WAY BTWN W140 AND W150. THEN LOST AUTOTHROTTLES; LAV AND VNAV. CAPT ASSUMED MANUAL CTL OF ACFT. DID NOT HAVE EICAS MESSAGE INDICATING 'FMC L' AT THIS TIME BUT CAPT ORDERED FO TO SELECT THE FMC MASTER SELECTOR SWITCH TO SELECT THE R FMC IN AN ATTEMPT TO RESTORE NAV. AUTOPLT WAS REENGAGED IN ALT AND HDG SELECT. ABOUT 4 MINS AFTER L CDU LOST PWR; PWR RETURNED. L CDU HAD LOST ALL STORED DATA AND R CDU HAD LOST SOME STORED DATA. REINSERTED DATA; SELECTED ACTIVE WAYPOINT; AUTOTHROTTLE; LNAV AND VNAV. REVIEWED IRREGULAR PROC 'FMC L.' PERFORMED POS PLOT TO VERIFY POS AT XB01Z. CONTACTED SAN FRANCISCO OCEANIC ON HF TO EXPLAIN THE LOSS OF LNAV. OPERATOR ADVISED LOSS OF CPDLC CONNECTION. REINSERTED DATA AND SENT POS RPT. CONTACTED DISPATCH AND MAINT ON SATCOM. POINTED OUT THE PREVIOUS HISTORY OF L CDU. CONTINUED FLT. BRIEFED MAINT ON ARR.

Data retrieved from NASA's ASRS site as of May 2009 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.