AFTER RECEIVING HIS PREFLIGHT WEATHER BRIEFING THE PILOT TOOK OFF IN HIS 166 HORSEPOWER, HEAVILY LOADED AIRPLANE, FROM AN AIRPORT WITH A DENSITY ALTITUDE OF 9,988 FEET MEAN SEA LEVEL. THERE IS NO EVIDENCE THAT THE PILOT CALCULATED THE DENSITY ALTITUDE OR THE AIRCRAFT'S PERFORMANCE PRIOR TO THE TAKEOFF. AS THE AIRCRAFT CLIMBED THROUGH 400 FEET ABOVE THE GROUND IT ENCOUNTERED A DOWN DRAFT AND BEGAN TO DESCEND. THE AIRCRAFT THEN BEGAN TO CLIMB AGAIN AND THE PILOT ENTERED A TURN TO RETURN TO THE AIRPORT. DURING THE TURN, THE AIRCRAFT ENTERED A DESCENT AND COLLIDED WITH THE TERRAIN.