THE PILOT HAD JUST COMPLETED TWO SWATH RUNS AND WAS TURNING TO START THE THIRD WHEN THE AIRCRAFT BEGAN TO BUFFET AND APPROACHED A STALL. THE PILOT THEN LOWERED THE NOSE OF THE AIRCRAFT AND ADDED FULL THROTTLE. AFTER APPLYING FULL THROTTLE THE PILOT STATED HE DID NOT HEAR THE ENGINE RESPOND. AS THE AIRCRAFT APPROACHED THE GROUND THE PILOT STATED HE APPLIED BACK PRESSURE '....SEVERAL TIMES WITH NEAR STALL CONTROL FEELINGS', BUT THE AIRCRAFT CONTINUED IT'S UNCONTROLLED DESCENT AND SUBSEQUENTLY CLIPPED SOME TREES BEFORE IMPACTING THE GROUND. ALTHOUGH A WITNESS STATED HEARING THE ENGINE BACKFIRE SHORTLY BEFORE IMPACT, DURING THE INVESTIGATION NOTHING WAS FOUND MECHANICALLY WRONG WITH THE ENGINE. THE WEATHER CONDITIONS AT THE TIME OF THE ACCIDENT DO CORRELATE WITH THE RANGE OF CONDITIONS ASSOCIATED WITH THE FORMATION OF CARBURETOR ICE, AND THE ENGINE, ACCORDING TO THE PILOT AND WITNESS STATEMENTS, DID EXHIBIT SOME INDICATIONS THAT CARBURETOR ICE MAY HAVE FORMED.