The O'Hare Airport UFO (2006)
On November 7, 2006, several United Airlines employees at Chicago O'Hare watched a grey disc hovering over gate C17 before it shot up through the clouds, punching a clean hole in the overcast. The FAA first called it a "weather phenomenon."
Witnesses
Airport staff
Why it endures
Aviation professionals, at a major airport, and a hole punched in the clouds.
Official version (contested)
The FAA held no investigation ("a reflection"). The witnesses, though, are adamant.