An air carrier flight; eastbound over the pacific ocean; suffered a single IRS failure and eventual ...

Narrative:

During cruise flight; we received a warning on the FMC; 'verify position: IRS-IRS.' we noted that the left IRS was showing a very large error; over 25 miles at the time and growing. We consulted the qrc; fom; flight handbook and systems manual for guidance as to specifically what the error meant and how to handle it. We cross checked our remaining navigation information and determined the right IRS was working properly. We notified dispatch via ACARS; and contacted commercial radio to let them know of our navigation failure as per guidance in our manuals. We continued to carefully monitor and cross check our position and performed several extra plots on our plotting chart to ensure our position was correct. Our position was indeed correct operating on the good IRS. We also began monitoring a coastline VOR as soon as it was in range and used it as an additional check to continuously verify our position. After radar contact with center; and after beginning our descent the left IRS generated a fault annunciation and apparently failed as the captain's flight instruments failed. The first officer then became the pilot flying. We then declared an emergency and got radar vectors to the airport. The checklist was consulted and that restored adequate instrumentation for the captain to continue flying. We then landed uneventfully and wrote the discrepancy in the aircraft logbook.

Original NASA ASRS Text

Title: An air carrier flight; eastbound over the Pacific Ocean; suffered a single IRS failure and eventual loss of the Captain's flight instruments. The flight continued utilizing the First Officer's instruments and IRS data.

Narrative: During cruise flight; we received a warning on the FMC; 'VERIFY POS: IRS-IRS.' We noted that the left IRS was showing a very large error; over 25 miles at the time and growing. We consulted the QRC; FOM; Flight Handbook and Systems Manual for guidance as to specifically what the error meant and how to handle it. We cross checked our remaining navigation information and determined the right IRS was working properly. We notified Dispatch via ACARS; and contacted Commercial Radio to let them know of our navigation failure as per guidance in our manuals. We continued to carefully monitor and cross check our position and performed several extra plots on our plotting chart to ensure our position was correct. Our position was indeed correct operating on the good IRS. We also began monitoring a coastline VOR as soon as it was in range and used it as an additional check to continuously verify our position. After radar contact with Center; and after beginning our descent the left IRS generated a FAULT annunciation and apparently failed as the Captain's flight instruments failed. The First Officer then became the pilot flying. We then declared an emergency and got radar vectors to the airport. The checklist was consulted and that restored adequate instrumentation for the Captain to continue flying. We then landed uneventfully and wrote the discrepancy in the aircraft logbook.

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.

Attributes
ACN	1089915
Time
Date	201305
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	INS / IRS / IRU
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Critical

An air carrier flight; eastbound over the pacific ocean; suffered a single IRS failure and eventual loss of the captain's flight instruments. The flight continued utilizing the first officer's instruments and IRS data.