THE HELICOPTER TOOKOFF ON AN AIR AMBULANCE FLT AT ABOUT 1219 PST. ACCORDING TO TOWER PERSONNEL, THE DEPARTURE APPEARED NORMAL. RADAR SERVICE WAS TERMINATED AT 1227 & THERE WAS NO FURTHER RADIO CONTACT WITH THE HELICOPTER. LATER, THE HELICOPTER WAS FOUND WHERE IT HAD CRASH LANDED ON STEEP MOUNTAINOUS TERRAIN, ROLLED OVER & BURNED. AN INVESTIGATION REVEALED AN OPEN LOGBOOK ENTRY THAT THE #1 TORQUE TRANSMITTER WAS INOP. A PERSON NEAR THE DEPARTURE POINT NOTICED THE L ENG COWLING WAS LOOSE. A SHORT TIME LATER, A 3' X 4' PIECE OF ENG COWLING WAS OBSERVED TO FALL FROM THE HELICOPTER. THERE WAS NO INDICATION IN THE AIRCREW'S RADIO TRANSMISSIONS THAT THEY WERE AWARE OF THE COWLING PROBLEM. AN EXAM REVEALED EVIDENCE THAT THE COWLING STANDOUT TUBE FOR THE L ENG HAD RUBBED AGAINST THE FREE WHEELING TURBINE GOVERNOR CABLE. AEROSPATIALE PSNL SAID THIS COULD DECREASE FUEL FLOW TO THE L ENG; AT HI POWER, THE R ENG GOVERNOR WOULD THEN INCREASE ITS FUEL FLOW & EXCEED LIMITS UNLESS PLT COMPENSATED. R FUEL SHUTOFF VALVE WAS FOUND NEAR ITS CLOSED POSITION.