Narrative:

Weather at lax was VFR. The riivr two arrival into lax depicts using the approach to runway 25L. Knowing we had a 50/50 chance of getting 24R; I decided to hold off loading the ILS 24R with riivr transition. I briefed the appropriate portion of the arrival and both the visuals to 24R and 25L as the weather was VFR (but didn't load anything). We maintained 280 KIAS as requested by approach. Passing rustt; approach told us to slow to 250 KIAS. I loaded 250 in the descent page and the autopilot responded appropriately with VNAV and autothrottles engaged. Approach control did not assign us a runway until just past hasbo. At that time the autopilot was set holding 250 KIAS with autothrottles and VNAV engaged. Approach then assigned us runway 24R off of the riivr arrival. The captain loaded the ILS 24R with riivr transition. At the same time we both incorrectly decided to put 2;200 MSL into the MCP altitude window since VNAV and a/T were engaged. The program was executed passing riivr and slightly below 12;000 MSL. After executing the program; the autopilot immediately began slowing the aircraft. I noticed the descent page target speed went to 193/flaps instead of maintaining 250 until 10;000 MSL. We both were momentarily confused as to why the autopilot wanted to slow. This was a problem since approach wanted us at 250 KIAS. After about 4-5 seconds; the captain noticed the 'at or above (xxxA)' altitudes assigned to each point on the ILS 24R; riivr transition on the legs page. He mentioned that this was the cause and correctly decided to load 'hard' altitudes. As he did this; my instincts were to disengage the auto throttle and VNAV system since it was not performing as I wanted it to. (I didn't realize until after touchdown that the autopilot wanted to slow to the FAF speed since it was the only hard altitude there - 2;200 feet). I announced performing these steps; but the captain and I had been having trouble hearing each other all day due to cockpit noise. He didn't hear me. At this time; the autopilot was holding roughly 1500 FPM in vertical speed mode. By the time the captain had re-executed the program with hard altitudes; we were already just below 10;000 MSL and inside minza on the ILS 24R. As he finished loading the hard altitudes; he went 'heads up' while I went 'heads down' to double check his inputs. When finished; I looked up and noticed we were approaching 9;300 MSL about 1.5 miles prior to skoll. (Skoll has a 10;000 feet altitude restriction.) I immediately noticed 2;200 feet was still in the MCP altitude window and selected 9000 feet while simultaneously reducing the descent rate to about 800 FPM in vertical speed and LNAV. As I did this; the captain became aware of the altitude bust and gave appropriate inputs. The remainder of the approach and landing were uneventful. Approach control never commented on the bust. First; regardless of what I thought I was going to expect; I should have loaded the appropriate approach and transition based on the riivr two arrival (in this case ILS 25L; riivr transition). I didn't want to have to load the approach twice so I waited. This was a mistake. Second; loading 2;200 in the MCP window (the FAF altitude) was simply not correct. The appropriate altitude in this case while in VNAV and a/T was 12;000. This is the last bold font altitude on the arrival. Per fom; that is when the a/T and VNAV should be disconnected. Had 2;200 not been in the window; there would have been no issues. Third; this was a wake up call on rnp; a/T; and VNAV. I thought I knew a lot about it; but realize there is more to learn. With the upcoming advanced training coming; we all could use a refresher. Fourth; back each other up. In the case above; we were both so busy with the last minute runway assignment; loading the approach in the box; and reacting to an unexpected autopilot input that we both lost sa which contributed to the altitude deviation.

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Original NASA ASRS Text

Title: Confusion reigned as the flight crew of a B737-700 struggled to comply with a runway change on the RIIVR STAR to LAX. Lack of facility with and understanding of the B737-700 VNAV functions of the FMS and poor cockpit discipline result in an altitude deviation.

Narrative: Weather at LAX was VFR. The RIIVR TWO Arrival into LAX depicts using the approach to Runway 25L. Knowing we had a 50/50 chance of getting 24R; I decided to hold off loading the ILS 24R with RIIVR transition. I briefed the appropriate portion of the arrival and both the visuals to 24R and 25L as the weather was VFR (but didn't load anything). We maintained 280 KIAS as requested by Approach. Passing RUSTT; Approach told us to slow to 250 KIAS. I loaded 250 in the descent page and the autopilot responded appropriately with VNAV and autothrottles engaged. Approach Control did not assign us a runway until just past HASBO. At that time the autopilot was set holding 250 KIAS with autothrottles and VNAV engaged. Approach then assigned us Runway 24R off of the RIIVR Arrival. The Captain loaded the ILS 24R with RIIVR transition. At the same time we both incorrectly decided to put 2;200 MSL into the MCP ALT window since VNAV and A/T were engaged. The program was executed passing RIIVR and slightly below 12;000 MSL. After executing the program; the autopilot immediately began slowing the aircraft. I noticed the descent page target speed went to 193/flaps instead of maintaining 250 until 10;000 MSL. We both were momentarily confused as to why the autopilot wanted to slow. This was a problem since Approach wanted us at 250 KIAS. After about 4-5 seconds; the Captain noticed the 'at or above (xxxA)' altitudes assigned to each point on the ILS 24R; RIIVR transition on the LEGS page. He mentioned that this was the cause and correctly decided to load 'hard' altitudes. As he did this; my instincts were to disengage the auto throttle and VNAV system since it was not performing as I wanted it to. (I didn't realize until after touchdown that the autopilot wanted to slow to the FAF speed since it was the only hard altitude there - 2;200 feet). I announced performing these steps; but the Captain and I had been having trouble hearing each other all day due to cockpit noise. He didn't hear me. At this time; the autopilot was holding roughly 1500 FPM in vertical speed mode. By the time the Captain had re-executed the program with hard altitudes; we were already just below 10;000 MSL and inside MINZA on the ILS 24R. As he finished loading the hard altitudes; he went 'heads up' while I went 'heads down' to double check his inputs. When finished; I looked up and noticed we were approaching 9;300 MSL about 1.5 miles prior to SKOLL. (SKOLL has a 10;000 feet altitude restriction.) I immediately noticed 2;200 feet was still in the MCP ALT window and selected 9000 feet while simultaneously reducing the descent rate to about 800 FPM in Vertical Speed and LNAV. As I did this; the Captain became aware of the altitude bust and gave appropriate inputs. The remainder of the approach and landing were uneventful. Approach Control never commented on the bust. First; regardless of what I thought I was going to expect; I should have loaded the appropriate approach and transition based on the RIIVR TWO Arrival (in this case ILS 25L; RIIVR transition). I didn't want to have to load the approach twice so I waited. This was a mistake. Second; loading 2;200 in the MCP window (the FAF altitude) was simply not correct. The appropriate altitude in this case while in VNAV and A/T was 12;000. This is the last bold font altitude on the arrival. Per FOM; that is when the A/T and VNAV should be disconnected. Had 2;200 not been in the window; there would have been no issues. Third; this was a wake up call on RNP; A/T; and VNAV. I thought I knew a lot about it; but realize there is more to learn. With the upcoming advanced training coming; we all could use a refresher. Fourth; back each other up. In the case above; we were both so busy with the last minute runway assignment; loading the approach in the box; and reacting to an unexpected autopilot input that we both lost SA which contributed to the altitude deviation.

Data retrieved from NASA's ASRS site as of April 2012 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.