Two words you never want to hear coming from the control tower at San Francisco International Airport: alert three. It signals the most dangerous kind of crash or serious incident.
On Wednesday, emergency responders, airport personnel and volunteers rehearsed for just that kind of situation as part of SFO's annual exercise. Last year, the airport practiced for an active shooter response. This year's scenario was a plane crash in the Bay.
NBC Bay Area's Sam Brock has more in the video report above.