B737-700
Flight Crew Last 90 Days 148
Human-Machine Interface
ATC Issue All Types; Inflight Event / Encounter Other / Unknown
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Human Factors; Procedure; Aircraft; Airspace Structure
The purpose of this ASAP is to highlight a safety issue with SoCal during arrivals into LAX.  We all laugh; and expect changes in the arrival procedures into LAX.  This event illustrates the danger that we are faced with.  On our arrival; we had planned a 280 KT descent to comply with speed at KONZL.  During our descent; we were slowed from 280 to 260.  During a descent; it is difficult to slow and stay on descent path.  Our aircraft was heavy and not slowing very well.  After passing KONZL; we were given descent via; but sped up to 280 again.  Another programming requirement while complying with the various altitudes.  Shortly thereafter; we were slowed to 250.  After jumping through hoops with the FMC programming; were slowed to 230; then 170.  All with a 30 KT tailwind; attempting to maintain altitude restrictions as well as put the aircraft in a position to be stabilized on final approach.  During the arrival; the speed changes were so drastic; I went to the old school method of stepping to the next altitude and turned off the automation.  I can appreciate automation; but when confronted with the rapid speed change requirements on an LNAV/VNAV arrival; the task at hand becomes quite daunting and even confusing.  We were tired; but we both recognized the futility of trying to make automation work; so we reverted to old school procedures.  My point here is not to show my superiority; but to point out that the numerous speed changes we are frequently faced with are distracting and possibly dangerous.  I don't want to be the Crew that is too absorbed in making the automation work that they forget to fly the aircraft.  SoCal needs to pick a speed and go with it.  Multiple speed changes on an arrival lead to non-compliance with chart restrictions and could lead to a dangerous flight condition.  The situation doesn't sound that bad here on paper; but it is a concern; and I think that if we don't speak up to ATC; then to them it is tacit approval to continue with this dangerous practice.
B737 Captain laments the speed changes issued by ATC during the SEAVU 2 RNAV arrival to LAX.