FAILURE OF THE PILOT TO PROPERLY SECURE THE CARGO, WHICH ALLOWED A SHIFT IN THE CENTER OF GRAVITY DURING A MISSED APPROACH MANEUVER AND RESULTED IN SUBSEQUENT LOSS OF AIRCRAFT CONTROL AND FLYING SPEED. A FACTOR RELATED TO THE ACCIDENT WAS FAILURE OF THE PILOT TO ASSURE THE AIRPLANE WAS LOADED WITHIN ITS PROPER WEIGHT AND BALANCE LIMITATIONS.