Air carrier flight crew inattentiveness leads to descent through altitude restr on a STAR into lax.

Attributes
ACN	439990
Time
Date	199906
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : pdz.vor
State Reference	CA
Altitude	msl single value : 12000
Aircraft 1
Controlling Facilities	tracon : sct.tracon tower : cgi.tower
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : intermediate altitude
Route In Use	arrival star : pdz 3
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	439990
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine
Events
Anomaly	altitude deviation : overshoot non adherence : clearance non adherence : company policies non adherence : published procedure
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : became reoriented flight crew : overrode automation
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

On pdz arrival approaching tejay intersection, inadvertently went approximately 300 ft below while 1 mi short of fix. Was in VNAV with altitude set to 10000 ft per the arrival. ATC injected several speed reductions. First officer, flying, switched to flight level change mode to handle ATC speeds and this negated FMC altitude management protections. I was unaware of mode change and we had called out the 13000 ft call but due to task loading first officer descended through 12000 ft. We smoothly stopped descent and regained altitude with no comment from ATC, and no apparent traffic conflict per TCASII. Event occurred due to rapid pace of ATC speed fluctuations and navigation task loading as we were turning on the arrival and switching frequencys, etc. More verbalization of mode changes might have heightened my awareness. We will be more alert to task saturation and prioritizing in the future.

Original NASA ASRS Text

Title: ACR FLC INATTENTIVENESS LEADS TO DSCNT THROUGH ALT RESTR ON A STAR INTO LAX.

Narrative: ON PDZ ARR APCHING TEJAY INTXN, INADVERTENTLY WENT APPROX 300 FT BELOW WHILE 1 MI SHORT OF FIX. WAS IN VNAV WITH ALT SET TO 10000 FT PER THE ARR. ATC INJECTED SEVERAL SPD REDUCTIONS. FO, FLYING, SWITCHED TO FLT LEVEL CHANGE MODE TO HANDLE ATC SPDS AND THIS NEGATED FMC ALT MGMNT PROTECTIONS. I WAS UNAWARE OF MODE CHANGE AND WE HAD CALLED OUT THE 13000 FT CALL BUT DUE TO TASK LOADING FO DSNDED THROUGH 12000 FT. WE SMOOTHLY STOPPED DSCNT AND REGAINED ALT WITH NO COMMENT FROM ATC, AND NO APPARENT TFC CONFLICT PER TCASII. EVENT OCCURRED DUE TO RAPID PACE OF ATC SPD FLUCTUATIONS AND NAV TASK LOADING AS WE WERE TURNING ON THE ARR AND SWITCHING FREQS, ETC. MORE VERBALIZATION OF MODE CHANGES MIGHT HAVE HEIGHTENED MY AWARENESS. WE WILL BE MORE ALERT TO TASK SATURATION AND PRIORITIZING IN THE FUTURE.

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.