Narrative:

On the approach to lax the captain and I were expecting to land on runway 25L. We were on the riivr 2 arrival and ended up being cleared for runway 24R instead. The captain entered in the correct runway and the approach; I verified this before he entered this and was sure that we should then be set up for the correct runway. We were cleared to descend via the riivr 2 arrival. Being cleared via the arrival wasn't much of a problem as we were already cleared for a descent earlier and were already descending via VNAV and were already set up for the descent and approach. I was scanning for traffic and the captain was looking for a point on the arrival that we were cleared to cross and we both noticed after a bit that the FMS has re-entered runway 25L without any pilot input. I immediately put the plane into heading mode to align with runway 24R. We were once again told to descend via the arrival and noticed that we were high so I then descended the plane as best I could. The captain notified ATC that we would be unable to meet one of the crossing restrictions; ATC said that this wouldn't be a problem. After this the captain re-entered 24R again and we watched it go magenta on 24R but then skip and go to 25L right away. Using heading mode I had the plane on the localizer for 24R and we were cautioned that a B777 was set up on final to the south of us. The captain told me at this point that the best way to handle things was to then hand fly the plane which is what I did; and since the plane was having difficulties I just decided to fly the plane in raw data. I think that flight crews need to be made aware that this happened so they can be cautioned and careful. This could have been more difficult if we were IMC and so making things more difficult.

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Original NASA ASRS Text

Title: EMB-170 First Officer describes an FMS anomaly during approach to LAX that will not allow the approach to be changed from Runway 25L to Runway 24R as assigned by ATC. Runway 24R is entered twice and each time reverts back to 25L. A hand flown approach to Runway 24R is accomplished.

Narrative: On the approach to LAX the Captain and I were expecting to land on Runway 25L. We were on the RIIVR 2 arrival and ended up being cleared for Runway 24R instead. The Captain entered in the correct runway and the approach; I verified this before he entered this and was sure that we should then be set up for the correct runway. We were cleared to descend via the RIIVR 2 arrival. Being cleared via the arrival wasn't much of a problem as we were already cleared for a descent earlier and were already descending via VNAV and were already set up for the descent and approach. I was scanning for traffic and the Captain was looking for a point on the arrival that we were cleared to cross and we both noticed after a bit that the FMS has re-entered Runway 25L without any pilot input. I immediately put the plane into heading mode to align with Runway 24R. We were once again told to descend via the arrival and noticed that we were high so I then descended the plane as best I could. The Captain notified ATC that we would be unable to meet one of the crossing restrictions; ATC said that this wouldn't be a problem. After this the Captain re-entered 24R again and we watched it go magenta on 24R but then skip and go to 25L right away. Using heading mode I had the plane on the localizer for 24R and we were cautioned that a B777 was set up on final to the south of us. The Captain told me at this point that the best way to handle things was to then hand fly the plane which is what I did; and since the plane was having difficulties I just decided to fly the plane in raw data. I think that flight crews need to be made aware that this happened so they can be cautioned and careful. This could have been more difficult if we were IMC and so making things more difficult.

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.