"Can I guarantee the American flying public that the United States has the most safe and secure airspace in the world? And the answer to that is, absolutely yes, we do," he said.
The night was clear, the plane and helicopter were both in standard flight patterns and there was standard communication between the aircraft and the tower, Duffy said.
It was not unusual to have a military aircraft flying the river and an aircraft landing at the airport, he said. Asked if the plane was aware that there was a helicopter in the area, Duffy said he would say that the helicopter was aware that there was a plane in the area.
Asked about President Donald Trump suggesting in an overnight social media post that the collision could have been prevented, Duffy said, "From what I've seen so far, do I think this was preventable? Absolutely."