I am not a UFO-er, but I did find the 2006 Chicago International airport incident interesting:
“At approximately 16:15 CST on Tuesday, November 7, 2006, federal authorities at Chicago O’Hare International Airport received a report that a group of twelve airport employees were witnessing a metallic, saucer-shaped craft hovering over Gate C-17.
The object was first spotted by a ramp employee who was pushing back United Airlines Flight 446, which was departing Chicago for Charlotte, North Carolina. The employee apprised Flight 446’s crew of the object above their aircraft. It is believed that both the pilot and co-pilot also witnessed the object. Several independent witnesses outside of the airport also saw the object. One described a “blatant” disc-shaped craft hovering over the airport which was “obviously not clouds.” According to this witness, nearby observers gasped as the object shot through the clouds at high velocity, leaving a clear blue hole in the cloud layer.[1] The hole reportedly seemed to close itself shortly afterward.
According to the Chicago Tribune’s Jon Hilkevitch, “The disc was visible for approximately five minutes and was seen by close to a dozen United Airlines employees, ranging from pilots to supervisors, who heard chatter on the radio and raced out to view it.”[2][3] So far, no photographic evidence of the UFO has surfaced, although it was reported to Hilkevitch that one of the United Airlines pilots was in possession of a digital camera at the time of the sighting and may have photographed the event.[4] NARCAP has published a 155-page report, suggesting a presence of the object in account over O’Hare and has called for a government inquiry and improved energy-sensing technologies: “Anytime an airborne object can hover for several minutes over a busy airport but not be registered on radar or seen visually from the control tower, (it) constitutes a potential threat to flight safety.”[5]
https://en.wikipedia.org/wiki/2006_O%27Hare_International_Airport_UFO_sighting
The authorities say that this was weather phenomena, as they always do, which is not consistent with eyewitness observations, people who are in the aviation industry, and not cranks.
So, what is it likely to be? Certainly not aliens from outer space. It is possible that experimental aircraft are being tested. Why they would be revealed at a large airport, remains to be explained. But, nothing is served by going the X-files way and thinking that the aliens are out there. Why would they want to visit earth anyway if they are so smart? After observing the Left, they would have concluded that there is no intelligent life on Earth anyway.
http://www.heraldtribune.com/news/20070821/ohare-incident-worth-revisiting
https://web.archive.org/web/20080120232411/http://narcap.org/reports/008/TR8Bias1.htm
https://www.express.co.uk/news/weird/904005/Pentagon-UFO-real-truth-US-navy-aliens-may-exist
http://www.independent.co.uk/news/world/americas/ufo-pentagon-beyond-reasonable-doubt-video-us-navy-tracking-pilots-footage-unidentified-flying-a8127881.html
http://www.independent.co.uk/news/world/americas/ufo-video-us-navy-tracking-pilots-footage-unidentified-object-a8116356.html
https://www.youtube.com/watch?v=Lrfr06Sj3vQ