B737-700 Flight Crew reported the aircraft began an uncommanded climb at cruise. The Flight Crew determined that the L IRS system had failed and switched over to the R IRS system. The Flight Crew continued to destination airport with no further issues.
Synopsis
B737-700 Flight Crew reported the aircraft began an uncommanded climb at cruise. The Flight Crew determined that the L IRS system had failed and switched over to the R IRS system. The Flight Crew continued to destination airport with no further issues.
Narrative
En route ZZZ1 to ZZZ2; First Officer's leg at FL340 we had an un commanded rapid climb to FL350 at approximately (time). We got the aircraft under control and noticed the First Officers altimeter fluctuating wildly. We transferred controls to my side and notified ATC of the altitude deviation and started working the problem. We referenced the Quick Reference Handbook for FMC scratch pad messages IRS-R Drift and Verify POS: IRS-IRS. While working on those issues with the autopilot on the A side; all of the First Officer's PFD instruments displayed all flags with an IRS FAULT. We ran the Quick Reference Handbook for IRS FAULT; but could not fix it and continued flight to ZZZ2 with no autopilot/auto throttle. Being busy hand-flying and trying to manage the navigation problem we unintentionally neglected to notify Dispatch of our problem. We had already coordinated our arrival with ZZZ2 Operations and asked to have Maintenance meet the aircraft. Maintenance met us at the gate and I wrote up the IRS FAULT in the logbook. We then handed the aircraft over to Maintenance in ZZZ2.
Second reporter narrative
While cruising; en route from ZZZ1 to ZZZ2 near ZZZ3 at FL 340 with the autopilot engaged; the aircraft started a rapid un commanded climb to FL 350. I disconnected the autopilot and got the aircraft stabilized and transferred aircraft control to the Captain as my altimeter and airspeed were fluctuating wildly. We notified ATC of the deviation; re-stabilized at FL 340 and went to the Quick Reference Handbook to troubleshoot the problem. We had FMC messages of IRS-R Drift and Verify POS: IRS-IRS. While working this issue; the First Officer's instruments displayed all flags with an IRS FAULT annunciation. We ran the Quick Reference Handbook for IRS FAULT; but were unable to restore the First Officer's instruments. We notified ATC we were unable RVSM; got a lower altitude and the Captain hand-flew the aircraft to ZZZ2. We notified Ops and Maintenance at ZZZ2 but were very busy and neglected to notify Dispatch. Maintenance met us at the gate and I wrote up the IRS FAULT in the logbook. We then handed the aircraft over to Maintenance at ZZZ2.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.