( CNN ) -- Two crewmen aboard an Idaho Army National Guard helicopter died when it crashed Thursday night , according to Ada County Coroner Erwin Sonnenberg . Guard spokesman Col. Timothy Marsano said the Apache helicopter was on a training mission when it went down two miles south of the Boise Airport . `` It 's a very difficult evening for us in the Idaho National Guard , '' Marsano told CNN affiliate KBOI . `` We do n't know the reasons why . We ca n't speculate at this point . '' The military is investigating the crash site . `` The men and women of the Idaho National Guard are united in grief at the loss of two of our brothers in arms , who gave their lives while training to defend our nation , '' Idaho National Guard Cmdr . Maj. Gen. Gary Sayler told the affiliate . `` Today , our thoughts and prayers are with their families . '' CNN 's Greg Morrison contributed to this report .
The Idaho Army National Guard helicopter crashed near Boise Airport . The Apache helicopter was on a training mission . An investigation is underway .