Narrative:

While acting as PIC on a flight from msp to lse, I was cleared pilot's discretion from my cruising altitude at 11000' to 5000'. Approximately 35 mi northwest of lse, I reported out of 11000' for 5000' and I reported lse in sight. Approximately 20 mi out of lse, ZMP gave me a 15 degree turn to the right for vectors for the visibility approach and for traffic. Approximately 10 mi west of lse, minneapolis informed me that I was only cleared to 5000', and that I had not been cleared for the approach. I had descended through 5000' and was at 3600' when ATC corrected me. I was instructed to return to 4000' and turned right to a heading of 180 degrees and I complied. Shortly afterward, I was cleared for the visibility approach to runway 36 at lse. The problem as I see it stems from the tendency of a pilot of relax from being on the sharp edge on a day when the ceilings and visibilities are unlimited. Also, I believe a contributing factor was the fact that I reported the airport in sight a considerable distance out, and by the time I had descended from 11000' to 5000', I had it in the back of my mind somewhere that I had been cleared for the approach--an unconscious assumption. The corrective action on my part is to try to train myself to always be sharp and keep, especially during those times when things are going smoothly.

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Original NASA ASRS Text

Title: AIR TAXI PLT DESCENDS BELOW ASSIGNED. BELIEVES CLEARED FOR APCH.

Narrative: WHILE ACTING AS PIC ON A FLT FROM MSP TO LSE, I WAS CLRED PLT'S DISCRETION FROM MY CRUISING ALT AT 11000' TO 5000'. APPROX 35 MI NW OF LSE, I RPTED OUT OF 11000' FOR 5000' AND I RPTED LSE IN SIGHT. APPROX 20 MI OUT OF LSE, ZMP GAVE ME A 15 DEG TURN TO THE RIGHT FOR VECTORS FOR THE VIS APCH AND FOR TFC. APPROX 10 MI W OF LSE, MINNEAPOLIS INFORMED ME THAT I WAS ONLY CLRED TO 5000', AND THAT I HAD NOT BEEN CLRED FOR THE APCH. I HAD DSNDED THROUGH 5000' AND WAS AT 3600' WHEN ATC CORRECTED ME. I WAS INSTRUCTED TO RETURN TO 4000' AND TURNED RIGHT TO A HDG OF 180 DEGS AND I COMPLIED. SHORTLY AFTERWARD, I WAS CLRED FOR THE VIS APCH TO RWY 36 AT LSE. THE PROB AS I SEE IT STEMS FROM THE TENDENCY OF A PLT OF RELAX FROM BEING ON THE SHARP EDGE ON A DAY WHEN THE CEILINGS AND VISIBILITIES ARE UNLIMITED. ALSO, I BELIEVE A CONTRIBUTING FACTOR WAS THE FACT THAT I RPTED THE ARPT IN SIGHT A CONSIDERABLE DISTANCE OUT, AND BY THE TIME I HAD DSNDED FROM 11000' TO 5000', I HAD IT IN THE BACK OF MY MIND SOMEWHERE THAT I HAD BEEN CLRED FOR THE APCH--AN UNCONSCIOUS ASSUMPTION. THE CORRECTIVE ACTION ON MY PART IS TO TRY TO TRAIN MYSELF TO ALWAYS BE SHARP AND KEEP, ESPECIALLY DURING THOSE TIMES WHEN THINGS ARE GOING SMOOTHLY.

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.