B747 flight crew experiences compass failure during arrival and deviates from assigned track.

Attributes
ACN	878676
Time
Date	201003
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	B747 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	Vectors
Flight Plan	IFR
Component
Aircraft Component	Compass (HSI/ETC)
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Flight Instructor Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 150 Flight Crew Total 7000 Flight Crew Type 750
Person 2
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Air Traffic Control Military 21 Air Traffic Control Non Radar 11 Air Traffic Control Radar 25 Flight Crew Last 90 Days 120 Flight Crew Total 8500 Flight Crew Type 2500
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Deviation - Track / Heading All Types

Narrative:

As we were descending towards ZZZ; we received a vector over the ocean for traffic. Once clear we were cleared direct to the VOR. Because of some errors we had with our navigation equipment; we initially headed southwest a couple of miles before turning west towards the VOR. We had a discrepancy between what the captain's RMI was saying; and what the FMS was saying. The captain was the flying pilot and chose initially to follow the RMI. As we were trying to figure out what was happening; ATC told us we were south of course. The captain then followed the information our FMS was giving us and the trip finished uneventfully. The aircraft was written up for a multitude of avionics issues that started on our trip; a day earlier; and continued with our next flight from ZZZ.

Original NASA ASRS Text

Title: B747 flight crew experiences compass failure during arrival and deviates from assigned track.

Narrative: As we were descending towards ZZZ; we received a vector over the ocean for traffic. Once clear we were cleared direct to the VOR. Because of some errors we had with our navigation equipment; we initially headed southwest a couple of miles before turning west towards the VOR. We had a discrepancy between what the Captain's RMI was saying; and what the FMS was saying. The Captain was the flying pilot and chose initially to follow the RMI. As we were trying to figure out what was happening; ATC told us we were south of course. The Captain then followed the information our FMS was giving us and the trip finished uneventfully. The aircraft was written up for a multitude of avionics issues that started on our trip; a day earlier; and continued with our next flight from ZZZ.

Data retrieved from NASA's ASRS site as of April 2012 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.