On the afternoon of Nov. 7, 2006, pilots and airport employees at O'Hare International Airport in Chicago saw a disc-like object hovering over the tarmac for several minutes. Because nothing was tracked on radar, the [FAA] did not investigate. Yet radar is not a reliable detector of all aircraft. Stealth planes are designed to be invisible to radar, and many radar systems filter out signals not matching the normal characteristics of aircraft. Did it really make sense to entirely ignore the observations of several witnesses? The American government has not investigated U.F.O. sightings since 1969, when the Air Force ended Project Blue Book, an effort to scientifically analyze all sightings to see if any posed a threat to national security. Britain and France, in contrast, continue to investigate U.F.O. sightings. On Dec. 26, 1980, for instance, several witnesses at two [US] Air Force bases in England reported seeing a U.F.O. land. An examination of the site turned up indentations in the ground and a level of radiation in the area that was significantly higher than ordinary. More witnesses at the same base reported the U.F.O. again on subsequent nights. The deputy base commander reported that the aircraft aimed light beams into the most highly sensitive area of the base - a clear security breach.The United States ... should reopen investigations of U.F.O. phenomena. It would not imply that the country has suddenly started believing in little green men. It would simply recognize the possibility that radar alone cannot always tell us what's out there.