B737-700 flight crew track deviation resulted when the right IRS failed in flight.

Attributes
ACN	1332810
Time
Date	201602
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	INS / IRS / IRU
Person 1
Function	Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 217 Flight Crew Type 217
Person 2
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 190 Flight Crew Type 8497
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Deviation - Track / Heading All Types

Narrative:

[While] under center control; an IRS-right message; followed by an unable rnp message appeared on the FMC. Although LNAV was still active; the aircraft appeared to be right of the magenta navigation line. I believe we were about two miles right of course. I was the pilot monitoring. I notified ATC of the navigation error and he cleared us direct [to a new fix]. I asked ATC to ensure we appeared to be headed in the right direction; as I was not confident in the accuracy of the navigation at this point. ATC indicated it looked good to him.subsequent discussions with ATC resulted in our vacating rvsm airspace. At one point I switched the IRS switch to both on left. This disconnected the autopilot [and] it would not re-engage. I put the IRS switch back to both and reconnected the autopilot. The rnp value remained in acceptable limits for the remainder of the flight; although the right IRS remained inoperative.we landed uneventfully at our destination; logged the discrepancy in the logbook; and notified dispatch and maintenance.

Original NASA ASRS Text

Title: B737-700 flight crew track deviation resulted when the right IRS failed in flight.

Narrative: [While] under Center control; an IRS-Right message; followed by an unable RNP message appeared on the FMC. Although LNAV was still active; the aircraft appeared to be right of the magenta navigation line. I believe we were about two miles right of course. I was the pilot monitoring. I notified ATC of the navigation error and he cleared us direct [to a new fix]. I asked ATC to ensure we appeared to be headed in the right direction; as I was not confident in the accuracy of the navigation at this point. ATC indicated it looked good to him.Subsequent discussions with ATC resulted in our vacating RVSM airspace. At one point I switched the IRS switch to both on left. This disconnected the autopilot [and] it would not re-engage. I put the IRS switch back to both and reconnected the autopilot. The RNP value remained in acceptable limits for the remainder of the flight; although the right IRS remained inoperative.We landed uneventfully at our destination; logged the discrepancy in the logbook; and notified Dispatch and Maintenance.

Data retrieved from NASA's ASRS site 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.