B757 flight crew descending into bwi experiences a sudden 5 NM map shift and resultant track deviati...

Attributes
ACN	1044703
Time
Date	201210
Local Time Of Day	0001-0600
Place
Locale Reference	BWI.Airport
State Reference	MD
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Component
Aircraft Component	INS / IRS / IRU
Person 1
Function	First Officer
Qualification	Flight Crew Flight Instructor Flight Crew Flight Engineer Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 100 Flight Crew Total 20000 Flight Crew Type 10000
Person 2
Function	Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 240 Flight Crew Total 26460 Flight Crew Type 13000
Events
Anomaly	Aircraft Equipment Problem Critical

Narrative:

During taxi; take-off; climb and cruise; FMC function was normal; but just passing ravnn intersection on the RAVNN3 arrival at bwi; with no alert messages; both ADI maps shifted approximately 5 miles to the northwest; and remained 5 miles displaced from our visually confirmed position for the remainder of the flight including during final approach; and while parked at the gate at bwi. IRS monitor showed over 5 miles drift for all three IRS's. The in flight navigation deviation occurred when map shift first occurred after passing ravnn waypoint. ATC queried us at that time about out track on the STAR; and we were given radar vectors for a visual approach to runway 15R. There were no traffic conflicts or altitude deviations. Throughout the visual approach; both ADI maps continued to depict the airport as 5 miles northwest of its actual position; and at gate all indications (fix page; latitude/longitude. And drift) continued to show our gate position five miles from actual. Maintenance control issued an MEL for subsequent flight under non-RNAV restrictions.

Original NASA ASRS Text

Title: B757 flight crew descending into BWI experiences a sudden 5 NM map shift and resultant track deviation that is questioned by ATC. The error is verified visually during approach and again at the gate using the map display; fix page; and the IRS latitude and longitude. The system is MEL'd for the return flight.

Narrative: During taxi; take-off; climb and cruise; FMC function was normal; but just passing RAVNN Intersection on the RAVNN3 arrival at BWI; with no alert messages; both ADI maps shifted approximately 5 miles to the northwest; and remained 5 miles displaced from our visually confirmed position for the remainder of the flight including during final approach; and while parked at the gate at BWI. IRS monitor showed over 5 miles drift for all three IRS's. The in flight NAV deviation occurred when map shift first occurred after passing RAVNN waypoint. ATC queried us at that time about out track on the STAR; and we were given radar vectors for a visual approach to Runway 15R. There were no traffic conflicts or altitude deviations. Throughout the visual approach; both ADI maps continued to depict the airport as 5 miles northwest of its actual position; and at gate all indications (fix page; latitude/longitude. and drift) continued to show our gate position five miles from actual. Maintenance Control issued an MEL for subsequent flight under Non-RNAV restrictions.

Data retrieved from NASA's ASRS site as of July 2013 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.