Audio reveals the conversation between the control tower at Ronald Reagan National Airport (DCA) and an Army Black Hawk helicopter shortly before it collided with an American Airlines flight carrying 64 people on Wednesday. The aircraft then crashed into the Potomac River.
American Airlines Crash: Audio Captures ATC Conversation With Black Hawk Pilot

The news last evening stated the FAA preliminary review was the ATC team was short resources and a single controller has handling the workload of 2 people.
A recent review of the incident highlights the request by the chopper pilot to take on the responsibility for the separation of his aircraft with those around him and it appears he got it wrong.