The crash of an American Airlines passenger jet and a US Army Black Hawk helicopter near Reagan Washington National Airport has highlighted issues around the congested airspace shared by civilian and military aircraft over the US capital.
Military helicopters and passenger airplanes are a common sight along the Potomac River in the Washington region, where the collision happened.
The area is home to numerous military bases and three major airports.
There have been several near-miss incidents at Reagan National Airport that have sparked alarm, including a near-collision in May 2024 between an American Airlines jet and a small airplane and one in April 2024 between Southwest and JetBlue airplanes.
The close calls coincide with a shortage of air traffic controllers that has delayed flights and raised safety concerns across the United States.
The FAA in October opened an audit into runway incursion risks at the 45 busiest US airports after a series of near-miss incidents.
Reagan National is particularly busy. Over a three-year period ending in 2019, there were 88,000 helicopter flights within 48 kilometres of Reagan National Airport, including about 33,000 military and 18,000 law enforcement flights, the Government Accountability Office said in a 2021 report.
The mid-air collision occurred as the passenger jet flying from Wichita was approaching to land at Reagan.
Both aircrafts were on standard flight patterns
Radio communications between the air traffic control tower and the Black Hawk showed the helicopter crew knew the plane was in the vicinity.
US Transportation Secretary Sean Duffy said the flight paths of the two aircraft were not unusual for the area and that both the helicopter and the airplane had been flying standard flight patterns.
Of the three major airports in the region, Reagan National is closest to the capital. Because of the short length of its runways, over 90% of flights use its main runway, making it the busiest in the US, with over 800 daily takeoffs and landings.
That effectively means a takeoff or landing every minute during much of the day. Reagan is the 24th-busiest US airport by passengers.
Congress last year approved five new round trip flights to Washington.
Mr Duffy said the Federal Aviation Administration would "take appropriate action if necessary to modify flight paths" to ensure adequate separation between civilian airplanes and military helicopters.
Defense Secretary Pete Hegseth said an investigation had been launched by the Army and Defence Department.
Senator Jerry Moran, who heads a Senate aviation subcommittee, said the immediate focus was on trying to save lives but that after the mission was over, Congress would investigate what went wrong.
"Then we're going to find out what happened," Mr Moran said.
Incursion audit
A February 2023 near miss in Austin, Texas was a wake up call on the issue after a FedEx cargo plane that had been set to land on a runway on which a Southwest Airlines jet was also cleared to depart from.
The two planes came close to colliding when the FedEx plane was forced to overfly the Southwest plane to avoid a crash, two sources briefed on the matter said at the time.
Over the last two years, a series of near-miss incidents have raised concerns about US aviation safety and the strain on understaffed air-traffic-control operations.
The FAA's runway incursion audit will include a risk profile for each airport, along with identifying potential gaps in procedures, equipment, and processes, and recommendations to improve safety and is expected to be concluded in early 2025.
The FAA Air Traffic Safety Oversight Service is conducting the review and the agency added it "is committed to identifying and mitigating risk at every level."
To be sure, former FAA Administrator Mike Whitaker said last October the number of serious runway-incursion incidents had fallen by over 50%.
