Crews are back at the Potomac River to retrieve the submerged wreckage of an airliner and an army helicopter that collided in mid-air last week in the deadliest US air disaster since 2001.

Just offshore from the towering national monuments of Washington, a tall crane now hovers over the Potomac River. It casts a large shadow over the ongoing effort to understand what caused the collision of a passenger jet and a military helicopter last Wednesday as a new phase of the recovery started Monday.

Portions of the two aircraft that collided over the river on Wednesday night near Ronald Reagan Washington National Airport — an American Airlines jet with 64 people aboard and a US Army Black Hawk helicopter with three aboard — are being loaded on to flatbed trucks and will be taken to a hangar for investigation.

Crews working on recovery efforts for the D.C. plane crash are using a crane to lift segments of the American Airlines jet out of the Potomac River.

Salvage crews have recovered an engine and large pieces of fuselage and are working to retrieve a wing from wreckage of last week’s midair collision near Washington’s Reagan National Airport

Black boxes from both the airplane and helicopter involved in last week’s deadly crash have been recovered by the NTSB as salvage crews continue to pull the wreckage from the Potomac River. NBC News Correspondent Aaron Gilchrist reports from Arlington,