Army helicopter collision kills 3; all aviation units grounded for safety review

Two Army helicopters collided during a training exercise in the Alaskan mountains, killing three soldiers.
The cause of the collision is still under investigation, though weather and visibility do not appear to be factors.
In response, the Army issued a stand-down order for all aviation units to complete additional safety training.
The order comes after two fatal helicopter crashes in the past month that resulted in 12 total deaths.
A memorial service will be held for the soldiers killed in the Alaska crash.