C421 pilot started approach prior to being cleared.

Attributes
ACN	492390
Time
Date	200011
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : laa.airport
State Reference	CO
Altitude	msl single value : 6000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zdv.artcc
Operator	general aviation : personal
Make Model Name	Golden Eagle 421
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Route In Use	approach : instrument non precision arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : multi engine pilot : private pilot : instrument
Experience	flight time last 90 days : 15 flight time total : 2555 flight time type : 1175
ASRS Report	492390
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : clearance non adherence : published procedure
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance none taken : detected after the fact
Supplementary
Problem Areas	Weather ATC Human Performance Aircraft Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Transition from en route to approach and given clearance to a DME fix to begin a VOR approach to runway 18 at lamar (laa). It was night and I was IFR in the undercast below. The automated WX was 4200 ft overcast, 10 mi visibility with temperature of -4 degrees and dewpoint of -8 degrees. My RNAV unit was sticking and I did not program in the proper coordinates in time. The controller advised me, I corrected. ATC cleared me to the fix and thought I was cleared for the approach. I believed I was cleared for the approach and told to report at DME fix. I called the fix -- no ATC response -- and began the approach. ATC called to ask my altitude. I reported it, and ATC said I was not cleared for the approach and to level altitude. I was then cleared for the approach. I canceled IFR shortly thereafter and landing was uneventful.

Original NASA ASRS Text

Title: C421 PLT STARTED APCH PRIOR TO BEING CLRED.

Narrative: TRANSITION FROM ENRTE TO APCH AND GIVEN CLRNC TO A DME FIX TO BEGIN A VOR APCH TO RWY 18 AT LAMAR (LAA). IT WAS NIGHT AND I WAS IFR IN THE UNDERCAST BELOW. THE AUTOMATED WX WAS 4200 FT OVCST, 10 MI VISIBILITY WITH TEMP OF -4 DEGS AND DEWPOINT OF -8 DEGS. MY RNAV UNIT WAS STICKING AND I DID NOT PROGRAM IN THE PROPER COORDINATES IN TIME. THE CTLR ADVISED ME, I CORRECTED. ATC CLRED ME TO THE FIX AND THOUGHT I WAS CLRED FOR THE APCH. I BELIEVED I WAS CLRED FOR THE APCH AND TOLD TO RPT AT DME FIX. I CALLED THE FIX -- NO ATC RESPONSE -- AND BEGAN THE APCH. ATC CALLED TO ASK MY ALT. I RPTED IT, AND ATC SAID I WAS NOT CLRED FOR THE APCH AND TO LEVEL ALT. I WAS THEN CLRED FOR THE APCH. I CANCELED IFR SHORTLY THEREAFTER AND LNDG WAS UNEVENTFUL.

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.