ACCORDING TO THE COMMERCIAL PILOT, DURING THE INITIAL PORTION OF HIS DAYTIME CROSS COUNTRY FLIGHT HE PLANNED TO FLY BENEATH THE BASE OF THE TERMINAL CONTROL AREA (TCA). AFTER CLEARING THE TCA'S LATERAL BOUNDARY, THE PILOT ENCOUNTERED TURBULENCE AND INITIATED A CLIMB FROM HIS 4700 FOOT CRUISE ALTITUDE TO 7500 FEET MSL. UPON REACHING 5300 FEET MSL, A STRONG DOWNDRAFT WAS ENCOUNTERED. THE AIRPLANE LOST ALTITUDE AND COLLIDED WITH A 4800 FOOT MSL HILL.