Investigators have recovered the flight recorders—also known as black boxes—from both the commercial jet and the military helicopter involved in the mid-air collision near Reagan National Airport in Washington,

Officials say the conditions of the Potomac River are complicating recovery efforts of the bodies of the 67 presumed dead in a mid-air collision between American Airlines flight 5342 from Wichita and a military Black Hawk helicopter.

Rescue crews will return to the Potomac River on Friday morning as they continue searching for victims of Wednesday night’s deadly midair collision.