How dangerous are drones to aircraft?

Gatwick suspends flights amid fears of collisions with objects that could pose serious threatGatwick airport drone disruption – live updates
Full story: Gatwick flights remain suspendedAny midair collision with an object is dangerous to aircraft, as exemplified by the crash of US Airways Flight 1549 in January 2009. Capt Chesley Sullenberger steered a passenger jet carrying 155 people into the Hudson River after it hit a flock of Canada geese shortly after taking off from La Guardia airpor