By David Shepardson

WASHINGTON (Reuters) -The U.S. Federal Aviation Administration said on Thursday it was modifying helicopter routes at two international airports near Washington, D.C., months after an American Airlines jet collided with an Army Black Hawk helicopter near the capital.

The FAA said the route changes affect Baltimore/Washington Thurgood Marshall International Airport and Washington Dulles International Airport.

"These changes are a precautionary measure that will add an additional buffer between aircraft and increase the separation between helicopters and airplanes operating into and out of each airport," the FAA said.

The FAA said it was also making changes to traffic around Ronald Reagan Washington National Airport. The FAA has faced criticism from lawmakers, the National Transportation Safety Board and Transportation Secretary Sean Duffy for failing to act on reports of near-miss incidents before the January 29 mid-air collision killed 67 people.

In May, the FAA barred the Army from helicopter flights around the Pentagon after a May 1 close call that forced two civilian planes to abort landings.

The Army Black Hawk helicopter was above the maximum permitted altitude at the time of the crash.

The NTSB disclosed in March that since 2021 there had been 15,200 air separation incidents near Reagan Washington National Airport between commercial airplanes and helicopters, including 85 close-call events.

The FAA said Thursday it reduced the boundaries of zones near Reagan and added notes to the Reagan helicopter chart "to improve clarity around altitude and operational instructions."

In April, the FAA imposed new restrictions to prevent collisions between helicopters and passenger planes around the busy Harry Reid International Airport in Las Vegas, citing significant safety issues.

The FAA has also been scrutinizing airplane traffic flows around Hollywood Burbank Airport and Van Nuys Airport in the Los Angeles area, which are less than 10 miles apart and serve a wide mix of aircraft with closely spaced arrival and departure paths.

(Reporting by David Shepardson and Jasper Ward; editing by Diane Craft)