The Federal Aviation Administration has closed off most helicopter access to Ronald Reagan National Airport’s airspace after a deadly collision on Wednesday night involving an Army helicopter, officials said.

The closures, which were announced to the airspace’s approved users about 12 hours after the crash, effectively close off helicopter access to the north and south of the airport, said a helicopter pilot who was briefed on the decision by an F.A.A. email alert but requested anonymity in order to discuss what was described as an “eyes-only” message from the aviation agency.

Sean Duffy, the new secretary of transportation, confirmed the closure on Friday, saying it was an important step toward ensuring greater safety.

“The American people deserve full confidence in our aviation system and today’s action is a significant step towards restoring that trust,” Mr. Duffy said in a statement.

No end time for the restrictions was offered.

The decision was made after an Army Black Hawk helicopter collided with an American Airlines regional jet that was en route to the airport from Wichita, Kan. There were no survivors.

The change cuts off parts of two aerial helicopter routes commonly used by military and law-enforcement pilots along the Potomac and Anacostia Rivers.