THE PLT DEPD DAYTON, OH, AT ABOUT 0800 ON A FLT TO MACON, GA. HE MADE AN EN ROUTE STOP AT CROSSVILLE, TN. DUE TO WX ON HIS ROUTE, HE CHOSE TO FLY TO KNOXVILLE (DKX), TN, TO REFUEL, THEN GO DIRECT TO MACON. AFTER REFUELING AT DKX, THE PLT DEPD FOR A DIRECT FLT OVER THE MTNS. HE STATED THAT THE PEAKS WERE TOO HIGH AND HE FOUND A MTN VALLEY LEADING TO A PASS ACROSS THE RIDGE LINE. HE OBSERVED CUMULUS CLOUDS OVER THE PEAKS. BEFORE REACHING THE CREST, THE CLOUDS BEGAN TO MOVED IN AROUND HIM. HE STARTED A TURN BACK TO AVOID THE CLOUDS, BUT THE LNDG GEAR BRUSHED THE TREES. SUBSEQUENTLY, THE ACFT CRASHED. PERSONNEL HIKING IN THE AREA HEARD THE CRASH, FOUND THE ACFT, GAVE FIRST AID TO THE PLT, & OBTAINED HELP FROM PARK RANGERS. THE PLT WAS EVACUATED BY HELICOPTER AFTER DELAYS DUE TO THUNDERSTORMS IN THE AREA. THE PLT INDCD HE WAS TAKING PRESCRIPTION DRUGS. A TOXICOLOGY CHECK SHOWED HIS BLOOD CONTAINED 0.095 MG/L OF NORDIAZEPAM. CANNABINOIDS WERE DETECTED IN HIS URINE, BUT NONE WAS FOUND IN HIS BLOOD.