National Airlines Flight 41, a Boeing 747-135, N77772, was a scheduled passenger nonstop flight, operating from Miami International Airport, Florida, to Los Angeles International Airport, California. Departure, climb, and initial cruise at assigned Flight Level 310 were routine. At 1314 CST, approximately 50 miles southeast of Lake Charles, Louisiana, one jolt of turbulence was encountered. Crewmembers on the flight deck and in the forward section of the aircraft cabin described the jolt as light to moderate in intensity. In the rear cabin, the jolt was much more severe. Thirty-eight passengers and four stewardesses sustained injuries which ranged from minor to serious. After determining that weather conditions in the immediate area were not favorable for landing, and after receiving assurance from two physicians attending to the injured that there would be no danger if more extensive treatment was not administered immediately, the captain decided to continue the flight to Los Angeles. After requesting and receiving preferential air traffic control handling, Flight 41 proceeded to Los Angeles International Airport and landed at 14:25 PST. The National Transportation Safety Board determines that the probable cause of this accident was an encounter with sharp-gust convective turbulence during flight in instrument meteorological conditions while numerous occupants of the aircraft were unsecured by seatbelts even though the seatbelt sign was lighted. The Board also determines that a number of passengers were injured because priority was given by the stewardesses to regular passenger service duties rather than to the enforcement of seatbelt usage.