Date: 201208
Local time of day: 1201-1800
Location: LAX.Airport, CA
Flight conditions: VMC
Weather elements / visibility: 15
Light: Daylight
Aircraft: B767-300 and 300 ER
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Initial Approach
Airspace: Class B LAX
ATC / advisory: TRACON SCT
Aircraft component: FMS/FMC
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Flight Engineer; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Situational Awareness; Workload; Training / Qualification; Human-Machine Interface
Second reporter function: Pilot Not Flying; Captain
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance
Contributing factors: Chart Or Publication; Company Policy; Human Factors
Primary problem: Company Policy

Narrative: [We were] descending in accordance with SEAVU.SEAVU2 STAR. At the transition to ILS 25L procedure at LAX; we began a descent from 10;000 FT at LUVYN Intersection instead of maintaining 10;000 FT until KRAIN Intersection and then a descent to 9;000 FT on the ILS procedure at TAROC Intersection. I was the flying pilot and elected to use flight level change at LUVYN instead of VNAV due to sluggish response from the VNAV system and changes to assigned speed. ATC mentioned at KRAIN that we needed to be at 10;000 FT even though we descended to approximately 9;700 FT before catching our mistake and climbing back up to 10;000 FT. [We had] no further incidents after this point; uneventful landing.Our company procedure is to fly the STAR and Approach in VNAV and set each altitude on the step downs and reselect VNAV until reaching the Final Approach Fix. It is labor intensive and errors can occur when ATC issues changes to crossing altitudes and adjusts speeds (VNAV has a hard time re-computing). I think errors would be reduced if the company procedure was changed so that VNAV was used but the Final Approach Altitude (or ATC limit) was set and allow VNAV to step down in accordance with the FMC computed rates instead of continually re-selecting VNAV every time the step down altitude is captured. This would allow both pilots more time to monitor traffic; deal with ATC changes; as well as procedural compliance.


Second narrative: Our procedure of putting in each step down crossing altitude greatly increased the work load of the pilot not flying; especially on an arrival such as the one into LAX. VNAV is perfectly capable of maintaining the appropriate path; with the crew as a back up. Why complicate things with the addition of multiple actions to accomplish?


Synopsis: A B767 flight crew departed 10;000 MSL prior to crossing KRAIN when flying the ILS 25L to LAX.  They believed the use of FMS and the Altitude Alert setting for each crossing restriction--as opposed to setting the final altitude in the 'descent ladder' in the altitude alert and allowing VNAV to navigate the intermediate crossings--was a contributing factor.