B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 171; Flight Crew Type 12000
Aircraft Equipment Problem Critical; Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance
Aircraft; Chart Or Publication; Human Factors; Procedure
[We were] cleared to descend via RIIVR Arrival 24R. Confirmed VNAV/LNAV and started descent. [We were] given 300 KTS which was entered on the descent page. Just prior to MINZA; the aircraft did not level at 10;000. I stopped the descent and climbed back to 10;000. I looked at the MCP and VNAV was no longer engaged. Re-engaged VNAV and continued an uneventful approach and landing.
Just prior to MINZA the pilot flying used CWS pitch to stop the aircraft from continuing to descend when he observed it passing 10;000. The lowest altitude I saw was approximately 9;650.At that time we noticed VNAV was no longer engaged. We re-engaged VNAV and completed the approach and landing.
For reasons unknown the FMS on their B737-700 dropped out of VNAV while descending on the RIIVR RNAV STAR; Runway 24R at LAX. The aircraft descended about 400 FT below the crossing restriction at MINZA.