The maximum altitude for a helicopter to fly in the area is 200 feet. Since radar data is rounded to the nearest 100 feet, NTSB knew the helicopter was flying anywhere between 251 feet and 349 feet.

The National Transportation Safety Board said in an update on Tuesday that it obtained data, rounded to the nearest 100 feet, that showed the Black Hawk helicopter was flying at roughly 300 feet ...

Since the data was rounded to the nearest 100 feet, officials need additional information to verify data points from the Black Hawk. That will require recovering the aircraft from the water, ...