B757 crew descended below published altitude when they thought they were cleared for approach.

Attributes
ACN	478320
Time
Date	200006
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : lax.airport
State Reference	CA
Altitude	msl single value : 5000
Environment
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	ils localizer only : 24 r
Flight Phase	descent : approach
Route In Use	approach : instrument precision
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	478320
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance non adherence : published procedure
Independent Detector	other controllera other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance
Consequence	other
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Approach clearance runway 24R ILS at lax. Approaching civet we were given a clearance change to fly the mitts 1. We were cleared to snrkl and descended as published. I thought we were also cleared the ILS runway 24R. We were given a frequency change during the descent and arrival change. Between denay and nence at approximately 5000 ft the controller called and said he had been waiting for us before being cleared the approach. We completed the approach and landing without further incident. There appeared to be no traffic conflict on approach and landing and the controller made no further comments.

Original NASA ASRS Text

Title: B757 CREW DSNDED BELOW PUBLISHED ALT WHEN THEY THOUGHT THEY WERE CLRED FOR APCH.

Narrative: APCH CLRNC RWY 24R ILS AT LAX. APCHING CIVET WE WERE GIVEN A CLRNC CHANGE TO FLY THE MITTS 1. WE WERE CLRED TO SNRKL AND DSNDED AS PUBLISHED. I THOUGHT WE WERE ALSO CLRED THE ILS RWY 24R. WE WERE GIVEN A FREQ CHANGE DURING THE DSCNT AND ARR CHANGE. BTWN DENAY AND NENCE AT APPROX 5000 FT THE CTLR CALLED AND SAID HE HAD BEEN WAITING FOR US BEFORE BEING CLRED THE APCH. WE COMPLETED THE APCH AND LNDG WITHOUT FURTHER INCIDENT. THERE APPEARED TO BE NO TFC CONFLICT ON APCH AND LNDG AND THE CTLR MADE NO FURTHER COMMENTS.

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.