Adds no immediate Army comment, FAA declining comment, more details in paragraphs 4-13

By David Shepardson

WASHINGTON, March 11 (Reuters) - Two senators asked the U.S. Army to explain why it routinely failed to use a key safety system during helicopter training flights after a deadly collision in January between an Army Black Hawk helicopter and an American Airlines regional jet killed 67 people.

Senate Commerce Committee Chair Ted Cruz and Senator Jerry Moran, who heads an aviation subcommittee, on Tuesday also urged the head of Army Aviation to answer questions about the collision and to testify at a March 27 hearing on the crash.

The Black Hawk did not have a key safety system known as ADS-B operating at the time of the collision, investigators say.

ADS-B, or automatic dependent surveillance-broadcast, is an advanced surveillance technology that transmits an aircraft's location.

U.S. airline group Airlines for America last week called for military aircraft to be required to use ADS-B near large airports to broadcast their position to avoid collisions.

The Republican senators also wanted to know how often the Army transports flag officers by helicopter and how often it turns off ADS-B, an action permitted for military aircraft.

National Transportation Safety Board Chair Jennifer Homendy has agreed to testify at the hearing before the panel's aviation subcommittee that will examine preliminary findings of the January 29 crash.

The committee has also invited the acting head of the Federal Aviation Administration, Chris Rocheleau, and Brigadier General Matthew Braman, who is director of Army Aviation.

The FAA declined to say if Rocheleau would appear. The Army did not immediately respond to a request for comment.

Civilian airplanes must use ADS-B to broadcast their location, but the FAA in 2019 gave the military an exemption in rare circumstances. It appears the military is routinely failing to use the safety system in training flights, lawmakers say.

On Friday, Senator Maria Cantwell, the top Democrat on the Commerce Committee, pressed the Pentagon on its failure to use the system.

Transportation Secretary Sean Duffy said on Tuesday the department was continuing discussions with the Pentagon about what they should deploy. Last month, he said it was time to shrink unneeded military flights.

"If we have generals who are flying in helicopters for convenience through this airspace, that's not acceptable. Get a damn Suburban and drive - you don't need to take a helicopter," Duffy said.

(Reporting by David Shepardson; Editing by Leslie Adler and Jamie Freed)

((David.Shepardson@thomsonreuters.com; 2028988324;))