If changes aren't made, that near-miss becomes a mid-air collision,” one aviation safety expert said. “Unfortunately, that's what we had last night.”

A jet carrying 60 passengers and four crew members collided Wednesday with an Army helicopter while landing at Ronald Reagan National Airport near Washington, prompting a large search-and-rescue operation in the nearby Potomac River.

Fatal crashes of commercial aircraft in the U.S. have become a rarity. The last was in 2009 near Buffalo, New York.

Staffing levels at the air traffic control tower at Ronald Reagan National Airport were 'not normal for the time of day and volume of traffic,' according to a preliminary report

Wednesday’s crash has resurfaced concerns about the airport’s proximity to the river, narrow landing space and overcrowding. Despite the geographic and logistical challenges, Congress authorized 10 additional “slots,” or flights, to DCA’s daily flight schedule.

Police boats combed the banks of the Potomac River on Friday, moving slowly under rainy skies and scanning the shoreline as investigators sought clues into the midair collision that killed 67 people and raised questions about air traffic safety around the nation’s capital.

A jet with 60 passengers and four crew members aboard collided Wednesday with an Army helicopter while landing at Ronald Reagan National Airport near Washington, prompting a large search-and-rescue

Midair collision of passenger jet and military helicopter outside the nation's capital was the first mass fatality commercial air disaster in the US since 2009

An American Airlines plane and an Army helicopter collided Wednesday night near Ronald Reagan Washington National Airport.

An Army Black Hawk helicopter collided with a regional jet near Ronald Reagan Washington National Airport on Wednesday evening, U.S. officials confirmed to ABC News.

Divers are expected to return to the Potomac River on Friday as part of the recovery and investigation after a midair collision killed 67 people.