All the 17 persons on-board were killed when an Ethiopian military helicopter crashed in Oromia regional state on Thursday, Ethiopia News Agency (ENA) reported.The Ethiopian Air Force helicopter had taken off early on Thursday from the city of Dire Dawa and was scheduled to arrive at the country's main Air Force base in Debre Zeit when it crashed about 50 km from its destination, Xinhua news agency reported.Among the 17 dead were two children and two women. An investigation is underway to determine the cause of the crash, ENA reported.