United States.O'Hare International

On 7 November 2006, in full daylight and shortly before sunset, United Airlines ground staff and pilots saw over Gate C17 at Chicago O'Hare airport a circular, dark-gray object of metallic appearance, with no lights and no sound. According to the Chicago Tribune, which spoke with the witnesses, it was motionless just below a cloud ceiling the FAA put at 1,900 feet (about 580 m); another estimate reported by the paper put it at about 1,500 feet and the first witness at 500–1,000, and size estimates ranged from 6 to 24 feet. Some saw it spinning like a Frisbee and others did not. After several minutes motionless, it shot upward through the cloud layer and, according to the witnesses, left a hole of clear air that closed within a few minutes ("It was like somebody punched a hole in the sky," one employee said). NARCAP's 2007 technical report reconstructed disparate timings: the first witness, a ramp worker directing the pushback of United flight 446 to Charlotte at Gate C17, saw it at about 4:30 pm and said it left about two minutes later, at about 4:32 pm; two mechanics moving an empty Boeing 777 saw it for at least three minutes sometime between 3:57 and 4:18 pm, and other witnesses give departure times up to 4:33 pm. NARCAP concluded the object may have been present for ten minutes or more.

As many as a dozen United employees reported it to the airline, among them mechanics, supervisors, ramp staff and pilots; the crew of flight 446 was alerted by radio and one of the pilots opened the cockpit window to get a better look. A manager left his office in Concourse B after hearing it on the internal frequency. The control tower saw nothing, and the FAA said a preliminary check of radar found nothing out of the ordinary. When Chicago Tribune reporter Jon Hilkevitch asked in late 2006, United's spokeswoman said there was nothing in the duty manager log and no record of the event, although several employees told the Tribune that the airline asked them to write reports and draw what they had seen and advised them not to talk about it.

The FAA also first said it had no information. After the Tribune's FOIA request, an internal review of communications tapes turned up a United supervisor's call to a tower manager, and spokeswoman Elizabeth Isham Cory attributed the sighting to a "weather phenomenon": a low ceiling and airport lights that, shining on the clouds, make people see "funny things". The FAA opened no investigation. NARCAP, a private group of aviation professionals and scientists led by former NASA researcher Richard F. Haines, filed its own FOIA requests and published a report of more than 150 pages in 2007. The certified recordings it received show three calls from United's ramp tower and an entry in the tower's daily record at 4:45 pm. In addition, a ground controller told an aircraft (Gateway 5668) at 3:58:09 pm to "use caution for the ah, UFO" and at 3:58:59 pm remarked to a colleague: "Somebody reported a UFO or a flying disc above Charley concourse, seriously." NARCAP itself notes that this time precedes the witnesses' own, and leaves open whether the tape's certified time is wrong or the object stayed over the airport for almost an hour.

Here the report of an object over a major commercial airport was recorded in the federal paperwork itself: the airline and the FAA first said they had no record, and the tower tapes and daily record, obtained through FOIA, show the report did reach the official system and was treated as a joke. What the case proves is that procedure; the nature of the object remains indeterminate. The Chicago Tribune coverage brought the subject back to mainstream journalism, and NARCAP's Richard F. Haines framed it as an air-safety problem: an unidentified object hovering over a terminal for minutes, with no radar return and unseen by the tower, is first of all an unreported operational risk.

The conventional explanations put forward have problems of their own. The FAA spoke of airport lights projected onto the clouds, but the event took place in full daylight and, according to NARCAP, the ramp lights had not yet been turned on. Astronomer Mark Hammergren, of the Adler Planetarium, told the Chicago Tribune in 2013 that conditions that day were right for a 'hole-punch cloud' or fallstreak: a hole that opens when an aircraft passes through a layer of supercooled droplets, which he said happens at temperatures near freezing. The weather data cut against it: the 4:51 pm O'Hare METAR recorded 12 °C at the surface, overcast at 1,900 feet and haze with 5 miles' visibility; the 6 pm Davenport sounding shows 8 to 13 °C in the lowest 2,000 feet and does not drop below 0 °C until about 3,100 metres, and NARCAP puts the freezing level at 10,000 feet, so the cloud in which the hole opened was made of water droplets that were not supercooled; for that reason the report rules out any freezing mechanism. Besides, the hypothesis accounts for the hole, not for the object the witnesses saw beneath it. Other conventional causes were raised at the time. On the ground controller's tape, at about 4:48 pm, one of the mechanics moving the 777 told him: "Oh, we saw it a half hour ago" and "We thought it was a balloon but we're not sure"; according to the Concourse B manager, another employee watched it for about thirty seconds and took it for a bird, and the manager himself thought somebody might be "bouncing a weather balloon or something else over O'Hare". NARCAP rejects a weather balloon, because the nearest sounding station is at Lincoln, some 135 miles away, and rules out any free balloon on two grounds: with a wind of about 7 knots a free balloon would have drifted more than a kilometre in five minutes and no witness saw any lateral movement, and the object rose far faster than a balloon. Haines told the Tribune he had determined that no weather balloon was launched near O'Hare that day, and the witnesses the paper spoke to ruled out a balloon. Neither NARCAP nor Haines examines a balloon that was not a weather balloon, and the five-minute stationary hover NARCAP assumes combines brief observations by different witnesses. Several witnesses did, however, see it rise at a slight angle to the east, the direction in which the west-south-westerly wind recorded by the METARs and by the sounding above the surface was blowing. Alan Boyle of MSNBC suggested a lenticular cloud or a vortex, and NARCAP dismisses it because of differences in size, altitude, appearance and motion and because of how stable the atmosphere was that day. A misperception (scale confusion or an object nobody identified) remains possible and is not ruled out by the absence of radar and tower witnesses, and the witnesses' timings do not agree with one another. NARCAP argues that the roof overhang hid the object from the tower, and the report speculates about an object able to evaporate the cloud, a calculation that starts from its hypothesis rather than from a measurement. The nature of the object remains unresolved, with several independent witnesses in favor of a real object and no conclusive instrumental measurement: NARCAP sees a "small chance" that the NEXRAD weather radar picked up a target near the cloud base, but doubts it itself, because the resolution cell covers about a square kilometre and similar echo appears, stronger, in an earlier scan when nobody was seeing anything.