B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 200; Flight Crew Total 16600; Flight Crew Type 391
Situational Awareness
ATC Issue All Types; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors; Procedure
After our initial descent out of cruise and before the outer marker; it became busy but manageable. We were doing well. Situational awareness; comm cadence; alertness; all quality high end work being done. Being sequenced behind two heavy B777's; so LA center and SoCal App were focused on us. From top of descent it started. 6 speed changes; one runway change; 3 descend via clearances after being vectored off the HLYWD 1 STAR; multiple altitude and heading changes; all programmed into the FMC for the 'highest mode of autopilot automation' that training taught us.However; one got away from us and we didn't catch it until ATC told us to level off at FL230. As the FMC was being updated with a new set of clearance instructions; the jet began a 1000 fpm rate of descent. I looked up and both of us verified the AVATR crossing between FL190-FL240. The problem was that we were 3 NM from BRUEN at FL240; when the jet started down. That crossing is FL240-FL300. Neither of us caught it and neither of us thought the jet was doing something we didn't want it to do. We are still not sure why this descent started nor did we investigate. I focused completely on the STAR crossing restrictions and QUIT with 'highest mode of operation' while on an RNAV STAR.
I was vectored off the arrival and given several descents putting us below VNAV path. We were given direct a point on the arrival and a descend via instruction at FL240. The point after the point I was cleared direct to contained an at or above FL240. When we dialed down the altitude to the lowest altitude of the arrival VNAV was not in path and began a cruise descent going below FL240. We were then told to maintain FL230 till past that point and then cleared for the approach.
B737 flight crew reported an arrival to LAX requiring multiple arrival changes; resulting in one crossing restriction that was missed.