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

on the committee overseeing aviation pressed the Pentagon on

Friday on the military's failure to use a key safety system in

routine helicopter flights around the U.S. capital region

following a deadly incident last month.

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.