THE PILOT-IN-COMMAND'S IMPROPER LOADING OF PERSONNEL, AND IMPROPER SUPERVISION OF THE FIRST OFFICER/CO-PILOT WHILE CALCULATING THE CENTER OF GRAVITY LIMITS FOR THE FLIGHT. THIS RESULTED IN THE FORWARD CENTER OF GRAVITY LIMIT BEING EXCEEDED AND SUBSEQUENT NOSE DOWN OF THE AIRPLANE ON THE RUNWAY DURING THE LANDING ROLL. CONTRIBUTING TO THE ACCIDENT WAS THE ABSENCE OF PASSENGER SEATS FOR THE CARGO LOADERS OR BALLAST IN THE REAR OF THE AIRPLANE AT THE TIME OF THE INCIDENT.