Narrative:

Flying a mooney M20E at approximately 7500 ft eastbound, I approached the houston class B airspace from idu on route to iws at approximately XA45 CDT. There was a scattered layer below me with ceiling approximately 4000 ft and tops at approximately 6000 ft. It was apparent that the undercast was denser towards the west, increasing to a broken, if not undercast layer. I contacted houston approach and requested clearance to transit their airspace on route to iws. I explained that there was an undercast layer, and that I would like to stay on top until I was closer to iws. I explained that the undercast layer looked denser to the west. Approach issued a transponder code and cleared me into the class B airspace. Approach cleared me to descend to the south. I told approach that cloud coverage was denser to the south, and that north would be preferable. Approach insisted that I descend to the south. I found an area of adequate cloud clearance to maintain VFR minimums for a descent, and began my descent to the south. As I descended, between the clouds, I initiated turns to maintain required VFR cloud clearance minimums. As I descended through approximately 5000 ft, approach issued the statement 'maintain 4500 ft.' I immediately advised that I was unable to maintain 4500 ft due to clouds, and requested lower altitude. At my position, I had clouds in front of me, and clouds on either side and behind. I could not climb fast enough to get above the clouds, and flying straight or deviating in either direction would have put me in IMC within seconds. Approach did not respond immediately. Approach issued a traffic notification to me and another aircraft. No other conflicting traffic was visible. In order to maintain VFR minimums, and to remain out of IMC, I continued my descent to approximately 3500 ft. Approach stated that I had not complied with the altitude assignment. I advised again that I was unable, and that I had requested lower. Approach then requested that I telephone upon landing. Upon landing, I telephoned approach and explained the cloud coverage situation and the necessity of descending in order to maintain VFR minimums and stay out of IMC.

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Original NASA ASRS Text

Title: AN M20 SINGLE PLT, FLYING VFR, WAS UNABLE TO COMPLY WITH THE ALT REQUEST MADE BY I90.

Narrative: FLYING A MOONEY M20E AT APPROX 7500 FT EBOUND, I APCHED THE HOUSTON CLASS B AIRSPACE FROM IDU ON RTE TO IWS AT APPROX XA45 CDT. THERE WAS A SCATTERED LAYER BELOW ME WITH CEILING APPROX 4000 FT AND TOPS AT APPROX 6000 FT. IT WAS APPARENT THAT THE UNDERCAST WAS DENSER TOWARDS THE W, INCREASING TO A BROKEN, IF NOT UNDERCAST LAYER. I CONTACTED HOUSTON APCH AND REQUESTED CLRNC TO TRANSIT THEIR AIRSPACE ON RTE TO IWS. I EXPLAINED THAT THERE WAS AN UNDERCAST LAYER, AND THAT I WOULD LIKE TO STAY ON TOP UNTIL I WAS CLOSER TO IWS. I EXPLAINED THAT THE UNDERCAST LAYER LOOKED DENSER TO THE W. APCH ISSUED A XPONDER CODE AND CLRED ME INTO THE CLASS B AIRSPACE. APCH CLRED ME TO DSND TO THE S. I TOLD APCH THAT CLOUD COVERAGE WAS DENSER TO THE S, AND THAT N WOULD BE PREFERABLE. APCH INSISTED THAT I DSND TO THE S. I FOUND AN AREA OF ADEQUATE CLOUD CLRNC TO MAINTAIN VFR MINIMUMS FOR A DSCNT, AND BEGAN MY DSCNT TO THE S. AS I DSNDED, BTWN THE CLOUDS, I INITIATED TURNS TO MAINTAIN REQUIRED VFR CLOUD CLRNC MINIMUMS. AS I DSNDED THROUGH APPROX 5000 FT, APCH ISSUED THE STATEMENT 'MAINTAIN 4500 FT.' I IMMEDIATELY ADVISED THAT I WAS UNABLE TO MAINTAIN 4500 FT DUE TO CLOUDS, AND REQUESTED LOWER ALT. AT MY POS, I HAD CLOUDS IN FRONT OF ME, AND CLOUDS ON EITHER SIDE AND BEHIND. I COULD NOT CLB FAST ENOUGH TO GET ABOVE THE CLOUDS, AND FLYING STRAIGHT OR DEVIATING IN EITHER DIRECTION WOULD HAVE PUT ME IN IMC WITHIN SECONDS. APCH DID NOT RESPOND IMMEDIATELY. APCH ISSUED A TFC NOTIFICATION TO ME AND ANOTHER ACFT. NO OTHER CONFLICTING TFC WAS VISIBLE. IN ORDER TO MAINTAIN VFR MINIMUMS, AND TO REMAIN OUT OF IMC, I CONTINUED MY DSCNT TO APPROX 3500 FT. APCH STATED THAT I HAD NOT COMPLIED WITH THE ALT ASSIGNMENT. I ADVISED AGAIN THAT I WAS UNABLE, AND THAT I HAD REQUESTED LOWER. APCH THEN REQUESTED THAT I TELEPHONE UPON LNDG. UPON LNDG, I TELEPHONED APCH AND EXPLAINED THE CLOUD COVERAGE SIT AND THE NECESSITY OF DSNDING IN ORDER TO MAINTAIN VFR MINIMUMS AND STAY OUT OF IMC.

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.