Investigators looking into the crash of a heavily loaded commuter plane that killed 18 people in Homer, Alaska, have focused on how the weight was distributed, a federal official said. The Ryan Air twin-engine turboprop, possibly coated with ice, smashed through an airport fence and belly-flopped onto snow-covered ground short of the runway last Monday as it tried to land in Homer. Three survived the crash. The plane, carrying its full capacity of 19 passengers and two crew members, had an estimated 16,100 pounds of cargo, its maximum allowable weight, said Barry Trotter, head of the National Transportation Safety Board. "The aircraft was designed to fly with that much weight," Trotter said. "It's where it's loaded in the aircraft that makes it critical. If you put it too far in the tail, it tends to be tail-heavy and makes it more critical flying."