The aviation world is struggling to understand how a deadly mid-air collision between a passenger plane and military helicopter was able to happen in what one expert described as "the most controlled bit of airspace in the world".
A US Army Black Hawk helicopter with a crew of three collided with an American Airlines jet carrying 64 people seconds before the passenger aircraft was due to land at Washington National airport.
Both aircraft were sent careering into the icy Potomac River on Wednesday night.
https://www.bbc.co.uk/news/articles/cpdx6le5l27o
img: Colin Brown, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons