The aircraft used by NOAA to conduct LiDAR scanning of the Potomac River early Friday. Photograph courtesy of Unified Command. LiDAR—which stands for “light detection and ranging”— uses laser light ...

The plane collided with a helicopter just before it was scheduled to land. This is a developing story and will be updated.

Upstream, the Potomac River is rising rapidly. At Point of Rocks, the river hit 21.5 feet by 4:45 a.m. Thursday and is projected to crest at 23.6 feet, rivaling water levels not seen since 1910.

The plane collided with a helicopter just before it was scheduled to land. This is a developing story and will be updated.