A U.S. Army Black Hawk crew may not have heard critical air traffic control messages instructing it to fly behind the commercial regional jet it ultimately collided with midair at Reagan National Airport in Washington on Jan. 29, the National Transportation Safety Board said Friday.

Additionally, the helicopter crew may have received inaccurate altitude data inside the cockpit, NTSB officials said at a media briefing at NTSB headquarters about the ongoing investigation.

The on-scene investigation of the collision of the American Airlines flight from Wichita, Kansas, and a UH-60 on a flight over the Potomac River has concluded, Jennifer Homendy, NTSB chair, said. The investigation will continue off-site in various labs and other secure locations.

When the aircraft collided, the fuselage of the commercial jet broke apart in three places and was discovered inverted in waist-deep water in the Potomac. The helicopter wreckage was found nearby. All 64 people aboard the passenger jet and all three Army crew members aboard the Black Hawk — Chief Warrant Officer 2 Andrew Loyd Eaves, Cpt. Rebecca M. Lobach and Staff Sgt. Ryan Austin O’Hara — were killed.

When asked if there was any indication the Black Hawk crew could see the impending collision in the seconds before impact, Homendy said NTSB investigators “do not have any indication” that the crew would have seen it.