In a tragic midair collision over Washington, DC, preliminary data suggests the pilots of an American Airlines flight tried to pull the plane’s nose up just seconds before crashing into a Black Hawk helicopter. The National Transportation Safety Board (NTSB) shared this finding as part of its ongoing investigation into the disaster, which is believed to have claimed 67 lives.

According to the NTSB, the plane’s flight data recorder showed a slight increase in pitch moments before the impact. Experts believe this could indicate the pilots attempted to avoid the helicopter at the last second. “It suggests they didn’t see the helicopter until it was almost too late,” said an aviation analyst.

The Black Hawk helicopter, which was training for emergency government evacuations, may have been flying above the allowed altitude of 200 feet in the restricted airspace. Initial reports indicate the plane was around 325 feet at the time of the crash, while air traffic control data placed the helicopter at 200 feet—a discrepancy investigators are working to clarify.

The collision occurred along the Potomac River, near Reagan National Airport, one of the busiest airspaces in the country. The Black Hawk’s black box has been recovered, but investigators are still analyzing the data. Meanwhile, crews are working to recover the wreckage and the remaining bodies from the river.

This marks the deadliest aviation disaster in the US since 2001. The NTSB expects to release a preliminary report within 30 days, but determining the probable cause could take much longer.

As the investigation continues, questions about air traffic control staffing and safety protocols in the area are also coming to light.