Narrative:

On descent into lax; we were cleared the riivr arrival and subsequently cleared to cross gramm at FL190. On being handed off to socal; we were directed to proceed to riivr for 24R; descend to 14;000 ft and maintain 300 KTS or greater. At that time I selected level change and set 14;000 ft in the altitude window to initiate the descent. The FMC had been previously programmed for runway 24R; so we verified the route and reprogrammed the descent page for 300 KTS. Subsequently; we were cleared for the ILS to 24R. My first officer and I both confirmed the routing and modes and I set 2;200 ft in the altitude window. Approaching 10;000 ft on the arrival; our attention was diverted by a loss of flight director bars on the first officer's ADI. At approximately 9;500 ft; I realized that we were not leveling or slowing. I disengaged the autopilot and started a climb back to 10;000 ft. At this time socal gave us a frequency change and stated we were low and directed us to maintain 9;000 ft and re-cleared us for the ILS 24R. The remainder of the approach and landing was uneventful.upon evaluation of this event; both the first officer and I felt we had confirmed an LNAV/VNAV descent and had set the appropriate altitudes. As we descended; I was crosschecking the legs page restrictions and we were on a good descent gradient. However; I obviously did not realize we were still in level change; which created the altitude issue. After reflecting on this event; I feel there were several contributing factors. First; I have become somewhat complacent with the LNAV/VNAV arrivals as they become routine and I have come to trust the machine. Additionally; I think that when we were confirming our descent mode; we saw what we wanted to see (descending on path at 300 KTS) not the mode that was actually engaged; level change. Finally my comfort level of having done the arrival hundreds of times contributed to me diverting my attention to something trivial at a time when my attention should have been on ensuring the LNAV/VNAV was doing what I wanted it to do. The lesson for me from this event is twofold. First and foremost is to trust but verify the machine. Second; and the more difficult; is to make much more of an effort to guard against complacency.

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Original NASA ASRS Text

Title: B737-500 flight crew reports an altitude deviation during the RIIVR 2 arrival to LAX when they are given direct to RIIVR from over GRAMM and 300 KTS or better. Level Change was selected for descent to 14;000 FT then forgotten when 2;200 is set for the final approach fix altitude.

Narrative: On descent into LAX; we were cleared the RIIVR Arrival and subsequently cleared to cross GRAMM at FL190. On being handed off to SoCal; we were directed to proceed to RIIVR for 24R; descend to 14;000 FT and maintain 300 KTS or greater. At that time I selected Level Change and set 14;000 FT in the Altitude window to initiate the descent. The FMC had been previously programmed for Runway 24R; so we verified the route and reprogrammed the Descent page for 300 KTS. Subsequently; we were cleared for the ILS to 24R. My First Officer and I both confirmed the routing and modes and I set 2;200 FT in the Altitude window. Approaching 10;000 FT on the arrival; our attention was diverted by a loss of flight director bars on the First Officer's ADI. At approximately 9;500 FT; I realized that we were not leveling or slowing. I disengaged the autopilot and started a climb back to 10;000 FT. At this time SoCal gave us a frequency change and stated we were low and directed us to maintain 9;000 FT and re-cleared us for the ILS 24R. The remainder of the approach and landing was uneventful.Upon evaluation of this event; both the First Officer and I felt we had confirmed an LNAV/VNAV descent and had set the appropriate altitudes. As we descended; I was crosschecking the LEGS page restrictions and we were on a good descent gradient. However; I obviously did not realize we were still in Level Change; which created the altitude issue. After reflecting on this event; I feel there were several contributing factors. First; I have become somewhat complacent with the LNAV/VNAV arrivals as they become routine and I have come to trust the machine. Additionally; I think that when we were confirming our descent mode; we saw what we wanted to see (descending on path at 300 KTS) not the mode that was actually engaged; Level Change. Finally my comfort level of having done the arrival hundreds of times contributed to me diverting my attention to something trivial at a time when my attention should have been on ensuring the LNAV/VNAV was doing what I wanted it to do. The lesson for me from this event is twofold. First and foremost is to trust but verify the machine. Second; and the more difficult; is to make much more of an effort to guard against complacency.

Data retrieved from NASA's ASRS site as of July 2013 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.