Five members of Taiwan\'s air force were missing Monday after a military helicopter plunged into high seas during a humanitarian mission, the defence ministry said. The helicopter had six crewmen on board when it plummeted into deep waters but one was successfully rescued, the ministry added. The S70-C air force helicopter plunged into waters around 70 nautical miles (129.64 kilometres) southeast of Lanyu, an island in the southeast Taitung county, at 9:25pm (1325 GMT). It happened as the helicopter was trying to transport a sick sailor from an Indonesian-registered vessel, it said. Rescuers retrieved one crew member but the rest, including two pilots, remained missing late Monday.