Pilots of an Air Canada flight out of Halifax reported seeing a drone 900 feet from their plane, at an altitude of 18,000 feet. The drone was tubular and had a vertical propeller. No commercially available drone has a radio range sufficient to enable it to fly to 18,000 feet, so either this was something constructed by a specialist, a military drone, or an unknown object. Whatever it was, it was doing something extremely dangerous and illegal.

Story Source:
http://thechronicleherald.ca/metro/1227797-mini-ufo-comes-close-to-jetliner