Burning odor aboard B777-200 is traced to avionics cooling fan.

Attributes
ACN	810810
Time
Date	200811
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 39000
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	B777-200
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Route In Use	arrival star : n/s
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 200 flight time total : 17500 flight time type : 2668
ASRS Report	810810
Events
Anomaly	aircraft equipment problem : less severe other anomaly
Independent Detector	other flight crewa
Resolutory Action	flight crew : declared emergency flight crew : overcame equipment problem
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

About 1 hour out of ZZZ over the ocean; we began smelling a very acrid burning plastic smell in the cockpit. I called the flight attendants and had them observe the cabin for smoke and fumes. They said the mid galley is also smelling of burning material with no smoke. We ran the smoke and fumes checklist followed by the smoke and fumes removal. We called dispatch and maintenance. Status messages showed a cooling fan shutdown. Maintenance said that they have a downlink showing an overheat of the fan. I have had this problem before where an avionics cooling fan burns up and shuts down but not after emitting a very strong burning odor throughout the cabin. The other fan starts up and protects the equipment. After following the checklists; the odor dissipated and we were sure that the source was positively idented. To be on the safe side; I declared an emergency and landed ZZZ without further incident. Once on the ground and clear of the runways; we canceled the emergency.

Original NASA ASRS Text

Title: BURNING ODOR ABOARD B777-200 IS TRACED TO AVIONICS COOLING FAN.

Narrative: ABOUT 1 HR OUT OF ZZZ OVER THE OCEAN; WE BEGAN SMELLING A VERY ACRID BURNING PLASTIC SMELL IN THE COCKPIT. I CALLED THE FLT ATTENDANTS AND HAD THEM OBSERVE THE CABIN FOR SMOKE AND FUMES. THEY SAID THE MID GALLEY IS ALSO SMELLING OF BURNING MATERIAL WITH NO SMOKE. WE RAN THE SMOKE AND FUMES CHKLIST FOLLOWED BY THE SMOKE AND FUMES REMOVAL. WE CALLED DISPATCH AND MAINT. STATUS MESSAGES SHOWED A COOLING FAN SHUTDOWN. MAINT SAID THAT THEY HAVE A DOWNLINK SHOWING AN OVERHEAT OF THE FAN. I HAVE HAD THIS PROB BEFORE WHERE AN AVIONICS COOLING FAN BURNS UP AND SHUTS DOWN BUT NOT AFTER EMITTING A VERY STRONG BURNING ODOR THROUGHOUT THE CABIN. THE OTHER FAN STARTS UP AND PROTECTS THE EQUIP. AFTER FOLLOWING THE CHKLISTS; THE ODOR DISSIPATED AND WE WERE SURE THAT THE SOURCE WAS POSITIVELY IDENTED. TO BE ON THE SAFE SIDE; I DECLARED AN EMER AND LANDED ZZZ WITHOUT FURTHER INCIDENT. ONCE ON THE GND AND CLEAR OF THE RWYS; WE CANCELED THE EMER.

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.