B757-200 crew descended below the altitude crossing restr at lax.

Attributes
ACN	590854
Time
Date	200308
Day	Wed
Local Time Of Day	0001 To 0600
Place
Locale Reference	intersection : snrkl
State Reference	CA
Altitude	msl bound lower : 11500 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : sct.tracon
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach
Route In Use	arrival star : mitts 1
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 200 flight time total : 10000 flight time type : 1000
ASRS Report	590854
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	altitude deviation : overshoot altitude deviation : crossing restriction not met non adherence : published procedure non adherence : far non adherence : company policies
Independent Detector	other flight crewa other flight crewb
Resolutory Action	none taken : anomaly accepted
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance FAA
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation other
Situations
ATC Facility	procedure or policy : sct.tracon

Narrative:

Prior to reaching civet intersection, we were cleared to the snrkl intersection and the mitts one arrival to runway 24R at lax. I was PNF, therefore, I performed the FMC work. I confirmed that the crossing restrs were programmed which included snrkl at or above 12000 ft MSL. Mins later the captain pointed out that there was a route discontinuity between the arrival and the approach. The length of time for the discussion and my correction in the FMC was approximately 10-15 seconds at which time I was 'heads down.' when I looked up, we were descending through 11700 ft MSL and still about 1 mi from snrkl intersection. I grabbed the control yoke to resist the autoplt at the same time commenting on the crossing restr. We crossed snrkl at 11500 ft MSL. I noticed the captain was in flight crewh mode. He then selected VNAV mode. I do not remember when the captain selected flight crewh so obviously I need to be more aware. I also could have disengaged the autoplt instead of resisting the force. I think my apprehension of disengaging the autoplt was because the captain was PF.

Original NASA ASRS Text

Title: B757-200 CREW DSNDED BELOW THE ALT XING RESTR AT LAX.

Narrative: PRIOR TO REACHING CIVET INTXN, WE WERE CLRED TO THE SNRKL INTXN AND THE MITTS ONE ARR TO RWY 24R AT LAX. I WAS PNF, THEREFORE, I PERFORMED THE FMC WORK. I CONFIRMED THAT THE XING RESTRS WERE PROGRAMMED WHICH INCLUDED SNRKL AT OR ABOVE 12000 FT MSL. MINS LATER THE CAPT POINTED OUT THAT THERE WAS A RTE DISCONTINUITY BTWN THE ARR AND THE APCH. THE LENGTH OF TIME FOR THE DISCUSSION AND MY CORRECTION IN THE FMC WAS APPROX 10-15 SECONDS AT WHICH TIME I WAS 'HEADS DOWN.' WHEN I LOOKED UP, WE WERE DSNDING THROUGH 11700 FT MSL AND STILL ABOUT 1 MI FROM SNRKL INTXN. I GRABBED THE CTL YOKE TO RESIST THE AUTOPLT AT THE SAME TIME COMMENTING ON THE XING RESTR. WE CROSSED SNRKL AT 11500 FT MSL. I NOTICED THE CAPT WAS IN FLT CREWH MODE. HE THEN SELECTED VNAV MODE. I DO NOT REMEMBER WHEN THE CAPT SELECTED FLT CREWH SO OBVIOUSLY I NEED TO BE MORE AWARE. I ALSO COULD HAVE DISENGAGED THE AUTOPLT INSTEAD OF RESISTING THE FORCE. I THINK MY APPREHENSION OF DISENGAGING THE AUTOPLT WAS BECAUSE THE CAPT WAS PF.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.