A B757-200 FLC DSNDS 400 FT PAST THEIR ASSIGNED ALT ON THE CIVET 4 ARR 40 MI NE OF LAX; CA.

Narrative

CLRED CIVET 4 ARR; DSCNT PROFILE; CROSS BREMR AT OR ABOVE 12000 FT. 3 MI PRIOR TO BREMR; ACFT PASSED 300-400 FT BELOW 12000 FT. APCH CTLR CAUGHT THE ALT ERROR AT SAME TIME CREW NOTICED. IMMEDIATELY CLBED ACFT TO 12000 FT AND CROSSED BREMR AT 12000 FT. CREW WAS FLYING A VNAV DSCNT AND APPARENTLY VNAV DSCNT WAS NOT CAPTURED. CAPT WAS READING APCH CHK AT TIME OF ALTDEV AND LOOKING AT APCH CHART. PRIOR TO APCH; DSCNT WAS BRIEFED AND ALL ALT RESTRS DISCUSSED. CIVET 4 ARR SELECTED IN FMS AND ALL ALTS CONFIRMED. THIS IS A VERY HIGH WORKLOAD ARR. IT REQUIRES TOTAL CREW CONCENTRATION AND ANY DISTR CAN RESULT IN AN ALTDEV; ESPECIALLY IF 1 CREW MEMBER IS INEXPERIENCED. I DON'T KNOW THE REASON FOR ALL THE ALT RESTRS; BUT IT'S VERY DIFFICULT TO FLY AND SHOULD BE MODIFIED WITH AN ENHANCED GS THAT CAN BE CAPTURED 40-50 MI OUT. SUPPLEMENTAL INFO FROM ACN 485462: APCHING 12000 FT; IT WAS APPARENT THAT THE ACFT WAS NOT GOING TO LEVEL OFF AT 12000 FT. AT THAT POINT; I INTERVENED USING THE VERT SPD MODE TO STOP THE DSCNT. SECONDS LATER; I DETERMINED THAT THE VERT SPD MODE WASN'T GONG TO BE AGGRESSIVE ENOUGH TO STOP THE DSCNT IN A TIMELY MANNER; SO I DISENGAGED THE AUTOPLT; STOPPED THE DSCNT AND CLBED BACK TO 12000 FT. THE CTLR NOTED NO CONFLICTS AND GAVE US A FREQ CHANGE.