B737-800
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Flight Crew Requested ATC Assistance / Clarification; General Declared Emergency
Aircraft
After the mid point we got an FMC message 'Verify Pos: IRS IRS.' We checked the POS SHIFT page; left IRS was at 26 NM and increasing. All other positions were within limits. ATC and Dispatch were notified at that time. ANP never was larger than 0.02. We referenced the Flight Handbook Supplemental Procedures section. In addition we made several extra plots using the right IRS from the overhead panel as a backup on our position. Aircraft position was never in doubt. Once over land we got an IRS fault with loss of the Captains PFD. We ran the QRH and made an un-eventful landing. An Emergency was declared with ATC after failure of the left IRS with the loss of the Captains PFD.
B737-800 Captain experiences the loss of a single IRS on an over water flight; just past the mid point; and continues to destination.