Descended below published altitude on localizer DME approach. Controller intervened.

Attributes
ACN	108036
Time
Date	198904
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : uki
State Reference	CA
Altitude	msl bound lower : 4000 msl bound upper : 6000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zoa
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Retractable Gear
Flight Phase	descent : approach
Route In Use	approach : straight in
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : private pilot : instrument
Experience	flight time last 90 days : 8 flight time total : 700 flight time type : 5
ASRS Report	108036
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : nmac non adherence : published procedure
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Flew VOR-a at uki, with missed, followed by localizer-DME at uki to landing. Cleared for approach while en route from eni VOR to kearn NDB, flying at 6000'. Upon passing kearn, I started descent to 4000'. I should have remained at 6000' until after procedure turn and established inbound on localizer. Cause: misinterp of approach plate, and over-reliance on controller's typical 'maintain XXX until established on the localizer, cleared for YYY approach...'. Discovered by controller noticing mode C readout and querying me as to my altitude. Corrective action: climbed to 5000' per ATC instructions.

Original NASA ASRS Text

Title: DESCENDED BELOW PUBLISHED ALT ON LOC DME APCH. CTLR INTERVENED.

Narrative: FLEW VOR-A AT UKI, WITH MISSED, FOLLOWED BY LOC-DME AT UKI TO LNDG. CLRED FOR APCH WHILE ENRTE FROM ENI VOR TO KEARN NDB, FLYING AT 6000'. UPON PASSING KEARN, I STARTED DSCNT TO 4000'. I SHOULD HAVE REMAINED AT 6000' UNTIL AFTER PROC TURN AND ESTABLISHED INBND ON LOC. CAUSE: MISINTERP OF APCH PLATE, AND OVER-RELIANCE ON CTLR'S TYPICAL 'MAINTAIN XXX UNTIL ESTABLISHED ON THE LOC, CLRED FOR YYY APCH...'. DISCOVERED BY CTLR NOTICING MODE C READOUT AND QUERYING ME AS TO MY ALT. CORRECTIVE ACTION: CLIMBED TO 5000' PER ATC INSTRUCTIONS.

Data retrieved from NASA's ASRS site as of August 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.