Narrative:

We were level at FL380 when the first officer commented that the airplane was turning left while we headed directly to a fix; in LNAV and VNAV. We also noticed that the first officer's vsi was indicating a climb of around 10;000 FPM while in level flight but mine was indicating correctly at 0 FPM. At that point; both nd's were indicating that our course was approximately 40 degrees to the left. There was a discrepancy on what heading we were actually flying between the map compass vs the pfd compass rose. At that point; the first officer's attitude indicator was showing a 30-40 degree bank to the right in straight and level flight. I disconnected the autopilot because we didn't know which instruments to trust quite yet and the heading bug was giving us erroneous information; so there was no way to couple the autopilot up to anything. We were in VMC on top of a solid layer of clouds. Shortly after that; the IRS and master caution light illuminated. It indicated an right IRS fault. I told the first officer that I would fly and he could run the QRH procedure and handle the radios. We ran the QRH procedure for an IRS [inertial reference system] fault and decided to attempt to get the first officer's attitude indicator working. After flying straight and level for more than one minute with the right IRS selector in att [attitude hold]; his ADI was still inoperative and showing a 45 degree bank to the right now. The IRS fault light went out because the IRS was in att now but the problem still remained. We talked about and agreed to put the IRS selector switch into both on left so the first officer would have reliable instruments instead of looking at an attitude indicator that was showing a 45 degree banked turn to the right. We talked about swapping arrivals and going VOR to VOR but ATC kept trying to give us fixes to fly direct to. At that point; we needed to start our descent and [advised ATC] because ATC was not understanding our inability to fly to fixes and it was getting really busy on the flight deck. They then asked us if we could intercept radials; and we replied yes. We swapped our nd's into VOR mode to navigate and get rid of the erroneous map displays. They gave us a heading to intercept the radial and descents along the way and we did that. I then transferred control of the airplane to the first officer while I [alerted] the flight attendants. We did not have time to contact [maintenance] or dispatch during that time because we'd be on the ground shortly. The approach and landing was uneventful.

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Original NASA ASRS Text

Title: B737NG flight crew reported loss of much of their nav capability following the failure of the right IRS.

Narrative: We were level at FL380 when the First Officer commented that the airplane was turning left while we headed directly to a fix; in LNAV and VNAV. We also noticed that the First Officer's VSI was indicating a climb of around 10;000 FPM while in level flight but mine was indicating correctly at 0 FPM. At that point; BOTH ND's were indicating that our course was approximately 40 degrees to the left. There was a discrepancy on what heading we were actually flying between the map compass vs the PFD compass rose. At that point; the First Officer's attitude indicator was showing a 30-40 degree bank to the right in straight and level flight. I disconnected the autopilot because we didn't know which instruments to trust quite yet and the heading bug was giving us erroneous information; so there was no way to couple the autopilot up to anything. We were in VMC on top of a solid layer of clouds. Shortly after that; the IRS and master caution light illuminated. It indicated an R IRS fault. I told the First Officer that I would fly and he could run the QRH procedure and handle the radios. We ran the QRH procedure for an IRS [Inertial Reference System] fault and decided to attempt to get the First Officer's attitude indicator working. After flying straight and level for more than one minute with the right IRS selector in ATT [Attitude Hold]; his ADI was still inoperative and showing a 45 degree bank to the right now. The IRS fault light went out because the IRS was in ATT now but the problem still remained. We talked about and agreed to put the IRS selector switch into BOTH on L so the First Officer would have reliable instruments instead of looking at an attitude indicator that was showing a 45 degree banked turn to the right. We talked about swapping arrivals and going VOR to VOR but ATC kept trying to give us fixes to fly direct to. At that point; we needed to start our descent and [advised ATC] because ATC was not understanding our inability to fly to fixes and it was getting really busy on the flight deck. They then asked us if we could intercept radials; and we replied yes. We swapped our ND's into VOR mode to navigate and get rid of the erroneous map displays. They gave us a heading to intercept the radial and descents along the way and we did that. I then transferred control of the airplane to the First Officer while I [alerted] the flight attendants. We did not have time to contact [Maintenance] or Dispatch during that time because we'd be on the ground shortly. The approach and landing was uneventful.

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.