The collision of American Airlines flight 5342 and an Army helicopter is the deadliest aviation disaster in the U.S. in 23 years. But there were warning signs. WSJ's Benjamin Katz reports on recent safety concerns about D.C.'s increasingly busy airspace and explains where the investigation goes next.

Further Listening:

-Your Flight Delay Is Probably New York's Fault 

Further Reading:

-How a Plane and a Helicopter Collided in a Crowded Airspace Around Reagan Airport 

-Washington’s Jam-Packed Airspace Has Prompted Warnings for Years 

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