2010-04 · NASA ASRS report 883679
B757 Flight Crew reports runway change by ZLA prior to KONZL on the SEAVU arrival to LAX; resulting in an altitude deviation at KONZL.
We were on the SEAVU arrival into LAX. ATC cleared us to cross KONZL at 17;000 FT. I was using vertical speed because VNAV had been inconsistent earlier during the flight. Approximately 5 NM from KONZL; as we were approaching 17;000 FT; but not yet in altitude hold; ATC simultaneously changed our runway assignment and cleared us for the descent via the arrival. I entered the next altitude in the window as the Captain reprogrammed the FMS for the new runway. A few seconds later; as we reviewed the new runway information; I realized we were descending through 16;700 FT and still 2.4 NM from KONZL. I quickly disengaged the autopilot and corrected to 17;000 FT as we crossed KONZL. I believe the altimeter touched 16;600 during my correction. We checked the TCAS and saw no aircraft within 5 NM at any altitude. ATC didn't mention our altitude deviation. My use of vertical speed combined with the altitude change just prior to level off (and therefore prior to ALT CAP) allowed vertical speed to briefly fly through our assigned altitude. Nothing new here. Just a reminder of good old fashioned pilot sense. Perhaps we had been missing some entry in the FMS which caused VNAV to work incorrectly. That caused a break in our habit patterns (using vertical speed instead of VNAV); which during a busy moment caused me to lose attention momentarily. In the future; I will make sure one pilot is always watching the plane and making sure it is conforming to the clearances (KONZL at 17;000) instead of both of us scrambling to implement multiple changes to our clearance.
Descending into LAX on the SEAVU STAR; I would say that it is probable that at ZLA/SOCAL will change runway assignment at least once during descent and approach; almost like they are trying to trick a pilot into a deviation. This flight was no different. The First Officer had been using VNAV; but it had started down way too early so he went back to vertical speed. Our runway assignment was changed back to the original 25L as we approached KONZL. As the Pilot Monitoring I again was 'heads down' resetting all the bugs and frequencies and reprogramming the FMC. Out of habit; the First Officer set 1;900 FT in the MCP; used to using VNAV still 2 miles outside of KONZL; so we descended through 17;000 FT by 200 or 300 FT. The airspace around LAX is unnecessarily dangerous with lots of 'gotchas'; like unusually low level off and airspeed constraints; plus the standard multiple runway/approach changes. When the approach is changed in the FMC; it basically forgets what it is doing; so a pilot can't trust it.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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