Date: 201302
Local time of day: 0601-1200
Location: SCT.TRACON, CA
Flight conditions: VMC
Light: Daylight
Aircraft: Challenger 605
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Flight phase: Descent
Airspace: Class B LAX
ATC / advisory: TRACON SCT
Aircraft component: FMS/FMC
Component problem: Design
Reporter organization: Corporate
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Human-Machine Interface; Time Pressure; Workload; Distraction; Confusion; Communication Breakdown
Second reporter function: Pilot Flying; Captain
Anomaly: Aircraft Equipment Problem Critical; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft; Human Factors; Procedure
Primary problem: Procedure

Narrative: While on the RIIVR RNAV STAR into LAX; we were cleared direct to GRAMM intersection. The PF briefed the ILS for Runway 25L and 24R; not knowing which was to be assigned. We continued on the arrival approaching RUSTT intersection at which point we were told to expect the ILS for 24R. Having already loaded the ILS for 25L (hopeful thinking); I proceeded to load the change in the FMS. Referring to the RIIVR Arrival; I didn't see a transition for the North complex and questioned SoCal if they still wanted us on the RIIVR Arrival; to which they responded 'affirmative'. At this time; we were approaching 14;000 feet MSL with VNAV selected. SoCal instructed us to expedite down to 10;000 feet and cleared us direct to SKOLL intersection. The PF selected 10;000 feet in the window and we both acknowledged the selection. As the PNF; I returned my attention to trying to load the FMS with the ILS for 24R; but couldn't find the transition from the RIIVR arrival. With the ILS 24R in the FMS; SKOLL intersection; did not appear. During this confusion; the controller came on with a very harsh scolding of our failure to expeditiously descend to 10;000 feet. Because I did not put a direct to SKOLL command in the FMS yet; with VNAV still active; the aircraft was maintaining 14;000 feet until passing HABSO. The Controller then came back with the statement that it looked as though we were lining up for 25L and instructed us to turn right to a heading [I've forgotten] to intercept the ILS 24R LOC. The PF immediately deselected VNAV; descended to 10;000 feet and made the turn to intercept the LOC for 24R. All this occurred within approximately a 30 second time frame. The remainder of the flight continued as planned.After landing; we debriefed the event quite extensively and in doing so; realized that there is a RIIVR transition for the ILS 24R in the FMS on the second page of transitions. Had I not focused on the Arrival and spent more time on the approach chart; I should have caught the oversight. It was also discussed that once an altitude clearance is assigned while on an arrival; deselecting VNAV should be a consideration. We both concluded that the combination of the time constraint and the 'colorful briefing' by the Controller only added to what had already become a high stress environment.


Second narrative: Prior to reaching RUSTT intersection on the RIIVR2 arrival; we were told by SOCAL to expect the ILS24R and to expedite the descent to 14;000 feet while maintaining 300K.The pilot monitoring asked the Controller if our clearance called for us to remain on the RIIVR2. SOCAL confirmed to remain on the arrival and to 'expedite the descent to 10;000 feet MSL.'[While] focusing on correctly programming the FMC; I did not realize that VNAV was still in 'PATH' and the autopilot had begun to shallow the descent to accommodate the 14;000 feet altitude restriction on the arrival at HABSO. This unexpected autopilot transition back to a VNAV descent occurred after executing the correct arrival and transition in the FMC.The Controller then told us to fly direct to SKOLL and cleared us for the ILS24R approach. The pilot monitoring reentered the ILS24R into the FMC which caused the transition from the arrival to the approach to drop out of sequence. I asked the pilot monitoring to enter any transition into the FMC just to get the fixes back into the FMC. After complying with my request; the pilot monitoring then executed a direct to SKOLL and we proceeded to fly the rest of the approach.


Synopsis: The flight crew of a corporate CL-605 cleared via the RIIVR STAR to LAX was caught short when Approach Control advised them to expect Runway 24R vice 25L as depicted on the arrival. Difficulty reprogramming the FMS for the new ILS resulted in autoflight remaining in VNAV PATH and the aircraft leveled at 14;000 feet instead of expediting to 10;000 feet as requested by Approach.