WASHINGTON, March 7 (Reuters) - The top Senate Democrat

on the committee overseeing aviation challenged the Pentagon on

Friday to justify not using a key safety system on routine

military helicopter flights in the U.S. capital region following

a deadly accident.

A U.S. Army helicopter that collided with an American

Airlines ( AAL ) regional jet in January near Washington's

Reagan Airport, killing 67, was not broadcasting ADS-B signals.

"It is not credible to assert that each of the several

thousand helicopter flights operated annually in the National

Capital Region is sufficiently sensitive to merit a blanket

exemption to operate without a critical safety feature like

ADS-B Out activated," said Senator Maria Cantwell in a letter to

Defense Secretary Pete Hegseth.

Civilian airplanes must use ADS-B, an advanced

aircraft-tracking technology, but the Federal Aviation

Administration in 2019 gave the military an exemption in rare

circumstances.

Cantwell, who serves on the Commerce Committee, said the

Pentagon "has gone far beyond the letter and spirit of this

regulatory exemption, despite the potential impact on aviation

safety."

The Pentagon did not immediately respond to a request

for comment.

Airlines for America, a U.S. airline trade group,

on Tuesday called for military aircraft

to be required to use ADS-B near large airports. It also

urged the FAA to permanently suspend some helicopter routes near

the Washington airport except for essential military or medical

flights.

Senator Ted Cruz, a Republican who chairs the Commerce

Committee, previously said, "There was no compelling national

security reason for ADS-B to be turned off" in the January

accident because the Army helicopter was on

a training mission

.