A small Indonesian Navy aircraft crashed off Sumatra island after trying to make an emergency sea landing Sunday, killing four officers and leaving three others missing, officials said. The Nomad, a twin-engine turboprop was carrying seven people, including the local Navy air base commander, Lt. Col. Suwito, when it crashed 10 minutes after takeoff from the small island of Sabang. "The four were probably killed on impact," Navy spokesman Rear Admiral Iskandar told Metro TV. It was not immediately clear why the pilot tried to make an emergency sea landing. Rescuers were combing the waters off Sumatra's northern coast for the missing officers, said Islamuddin, the deputy mayor of Aceh province. Like many Indonesians he uses only one name.