Pilot misunderstood STAR and left assigned altitude without a clearance.

Attributes
ACN	141347
Time
Date	199003
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ave
State Reference	CA
Altitude	msl bound lower : 10500 msl bound upper : 11000
Environment
Flight Conditions	Mixed
Light	Dusk
Aircraft 1
Controlling Facilities	tower : ako
Operator	general aviation : personal
Make Model Name	Small Aircraft
Flight Phase	cruise other descent other
Route In Use	arrival star : star enroute airway : v107
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 88 flight time total : 1570 flight time type : 1224
ASRS Report	141347
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance non adherence : published procedure
Independent Detector	other controllera
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation
Situations
Publication	Unspecified

Narrative:

ZLA was very busy! Understood that I was cleared to van nuys, fernando 2 arrival. When the STAR called for 9000 ft I commenced a descent from 11000 ft. At 10500 ft controller advised that mode C indicated 500 ft low. I responded that I was cleared fernando 2 arrival. He said those altitudes (on the STAR) are advisory only, assigned was 11000 ft, expect lower in 8 mi or so. I returned to 11000 ft. Remainder of trip was concluded without incident. I now believe that I commenced the descent prematurely at the VOR/changeover point, 63 DME southeast in error, but I am still not clear on whether or not a STAR clearance permits pilot to descend to the altitudes shown without further clearance. Callback conversation with reporter revealed the following: called reporter to counsel him on sids. He is now aware of the difference between a SID and a profile descent.

Original NASA ASRS Text

Title: PLT MISUNDERSTOOD STAR AND LEFT ASSIGNED ALT WITHOUT A CLRNC.

Narrative: ZLA WAS VERY BUSY! UNDERSTOOD THAT I WAS CLRED TO VAN NUYS, FERNANDO 2 ARR. WHEN THE STAR CALLED FOR 9000 FT I COMMENCED A DSCNT FROM 11000 FT. AT 10500 FT CTLR ADVISED THAT MODE C INDICATED 500 FT LOW. I RESPONDED THAT I WAS CLRED FERNANDO 2 ARR. HE SAID THOSE ALTS (ON THE STAR) ARE ADVISORY ONLY, ASSIGNED WAS 11000 FT, EXPECT LOWER IN 8 MI OR SO. I RETURNED TO 11000 FT. REMAINDER OF TRIP WAS CONCLUDED WITHOUT INCIDENT. I NOW BELIEVE THAT I COMMENCED THE DSCNT PREMATURELY AT THE VOR/CHANGEOVER POINT, 63 DME SE IN ERROR, BUT I AM STILL NOT CLEAR ON WHETHER OR NOT A STAR CLRNC PERMITS PLT TO DSND TO THE ALTS SHOWN WITHOUT FURTHER CLRNC. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: CALLED REPORTER TO COUNSEL HIM ON SIDS. HE IS NOW AWARE OF THE DIFFERENCE BETWEEN A SID AND A PROFILE DSCNT.

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.