Narrative:

Thought that there was possibility of a deflated left wing tire and had informed my company approximately 6 hours earlier. Company had apparently warned tower and approach control and emergency equipment was standing by. Extensive vectoring was done so that presumably emergency equipment could be positioned. Was on approximately 10 mi base to final for runway 1 at sdf and had previously been assigned 4000 ft and to intercept the localizer. My flight was level at 4000 ft and traffic was called to us at 12 O'clock and 2800 ft northbound (a landing aircraft that we were to follow). Aircraft was sighted and then noticed that my altitude was 3800 ft and descending. Stopped descent at 3700 ft and initiated climb back towards 4000 ft. Some time during these events, we were cleared for visual approach following the aforementioned traffic. I believe the clearance was at such close proximity to the time that we were cleared for the visual that there would be no official concern for an altitude bust. Nothing was mentioned about altitude transgression by the controller. Flight was handed off to tower and the remainder of the flight was uneventful. In retrospect, I left the 4000 ft early after having seen the traffic, but probably had not been cleared to do so for a period of several seconds.

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Original NASA ASRS Text

Title: CAPT OF A WDB ACR ACFT WITH A SUSPECTED FLAT MAIN WING LNDG GEAR TIRE ALLOWED THE ACFT TO PREMATURELY DSND BELOW INITIAL APCH ALT.

Narrative: THOUGHT THAT THERE WAS POSSIBILITY OF A DEFLATED L WING TIRE AND HAD INFORMED MY COMPANY APPROX 6 HRS EARLIER. COMPANY HAD APPARENTLY WARNED TWR AND APCH CTL AND EMER EQUIP WAS STANDING BY. EXTENSIVE VECTORING WAS DONE SO THAT PRESUMABLY EMER EQUIP COULD BE POSITIONED. WAS ON APPROX 10 MI BASE TO FINAL FOR RWY 1 AT SDF AND HAD PREVIOUSLY BEEN ASSIGNED 4000 FT AND TO INTERCEPT THE LOC. MY FLT WAS LEVEL AT 4000 FT AND TFC WAS CALLED TO US AT 12 O'CLOCK AND 2800 FT NBOUND (A LNDG ACFT THAT WE WERE TO FOLLOW). ACFT WAS SIGHTED AND THEN NOTICED THAT MY ALT WAS 3800 FT AND DSNDING. STOPPED DSCNT AT 3700 FT AND INITIATED CLB BACK TOWARDS 4000 FT. SOME TIME DURING THESE EVENTS, WE WERE CLRED FOR VISUAL APCH FOLLOWING THE AFOREMENTIONED TFC. I BELIEVE THE CLRNC WAS AT SUCH CLOSE PROX TO THE TIME THAT WE WERE CLRED FOR THE VISUAL THAT THERE WOULD BE NO OFFICIAL CONCERN FOR AN ALT BUST. NOTHING WAS MENTIONED ABOUT ALT TRANSGRESSION BY THE CTLR. FLT WAS HANDED OFF TO TWR AND THE REMAINDER OF THE FLT WAS UNEVENTFUL. IN RETROSPECT, I LEFT THE 4000 FT EARLY AFTER HAVING SEEN THE TFC, BUT PROBABLY HAD NOT BEEN CLRED TO DO SO FOR A PERIOD OF SEVERAL SECONDS.

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.