Updated Sunday at 7 p.m.
The Pentagon has now identified two soldiers killed in a helicopter crash at Fort Campbell late Friday night.
Ryan Connolly was a decorated instructor pilot with two Army air medals and deployments to both Iraq and Afghanistan. At 37, the Chief Warrant Officer 3 had been in the military since 2001.
Warrant officer James Casadona was 28 years old and just arrived at Fort Campbell earlier this year. The head of the 101st Combat Aviation Brigade called the deaths a "great tragedy."
Two soldiers were killed Friday night in a training accident at Fort Campbell on the Tennessee-Kentucky state line. The fatal crash follows a week of incidents for the military.
Just before 10 p.m., according to a 101st Airborne Division spokesperson, an Apache attack helicopter went down in the darkness on the sprawling Army post. No immediate cause was pinpointed.
Fort Campbell officials say both crew members were killed and that there were no other casualties.
"This is a day of sadness for Fort Campbell and the 101st Airborne," acting senior commander Brig. Gen. Todd Royar said in a statement. "Our thoughts and prayers are with the families during this difficult time."
The 101st Airborne specializes in helicopter assaults, meaning constant training and occasional crashes at Fort Campbell.
Last year, a Blackhawk troop carrier went down, injuring four. In 2015, an Apache incident killed two. A two-year investigation found that important bearings in the $25 million machine failed, likely due to improper maintenance.
At approximately 9:50 p.m. Friday, two Soldiers of the 101st Combat Aviation Brigade, 101st Airborne Division (Air Assault) were killed in an AH-64E Apache helicopter crash in the local training area on Fort Campbell. Go to https://t.co/pIKInAYO8s for more information.
— FortCampbell (@FortCampbell) April 7, 2018
Recent days have been particularly deadly for training across the military. Four Marines were killed in a California helicopter crash on Tuesday. And the next day, an Air Force fighter pilot died in a crash in Nevada.
At a Friday briefing, a Pentagon spokesperson refused to call the string of incidents a "wave" or "crisis." He said each is tragic and will be investigated.
But experts are trying to explain what might be happening. Aerospace expert Todd Harrison with the Center for Strategic and International Studies think tank in Washington, D.C., told Task & Purpose that pilots are often flying "old battle-worn aircraft."
"I think the high op tempo and stress on the force over the past 17 years of continuous combat operations in Iraq, Afghanistan, Syria, and elsewhere is catching up to the U.S. military,” he told the publication.
In 2017, 37 service members were killed in aviation training accidents across the military — more than double the figure from 2016. Arizona Sen. John McCain, chairman of the Senate Armed Services Committee and a former naval aviator himself, said the greatest harm to national security is "self-inflicted."
"We are killing more of our own people in training than our enemies are in combat," he said on the Senate floor.