It would be difficult to deny that a significant number of airline pilots encounter what they believe are UFO sightings during flight. A great deal of documented reports, RADAR images and photographic evidence exist to strongly support this unexplained phenomena, which by definition can be none other than unidentified flying objects.
Many examples in aviation history are documented, for example in December 1944 at an altitude of 10 000' the pilot and navigator of an allied aircraft flying over Germany at night encountered two large glowing balls unlike anything they had ever seen approaching rapidly from above. They leveled off and began to follow the aircraft and the pilot attempted every kind of evasive maneuver possible for several minutes in a vain attempt to shake his pursuers. Mimicking every twist, turn, dive and bank the balls of light remained in precise formation until for reasons unknown they suddenly accelerated at an unbelievable rate into a vertical climb and disappeared.
This was typical of many reports during day and night flying operations during WWII where aircraft were accompanied by these mysterious balls of light. Some pilots attempted to engage these objects believing they may be some form of advanced enemy weapon yet the speed and incredible maneuverability of these objects were no match for even the most advanced fighter aircraft of the day. These unidentified balls of light became known as FOO fighters by the pilots who encountered them however shortly after WWII the official Air Force position explained away these reports as ball lightning.
From June 1947 the US Air Force began to collect and investigate reports of UFO sightings by pilots and in March 1952 the infamous Project Blue Book officially commenced as the ambiguous conflict of a public front that described an officially secret' investigation into UFO sightings. Project Blue Book ended in January 1970 with a public statement that officially debunked UFO sightings as weather balloons, ball lightning or some other form of natural atmospheric light phenomena. From this point forward it became almost dangerous in terms of career prospects for any pilot to make any kind of official or public report of UFO sightings.
Countless reports continue to filter down and frequently star in pulp press describing UFO sightings by civilian airline pilots. It is rare indeed to read any reports on the front page of major newspapers; readers are more likely to find these encounters reported in the entertainment sections, or perhaps in some form of pseudo-scientific investigative reporter' story. This serves to maintain what seems clearly an official government position of denouncing the existence of UFOs.
Maintaining this official silence keeps the public guessing, few educational or research institutions of repute are willing to risk their academic prestige by formally acknowledging that which is against the norm. UFO reports and research are usually left to the fringe academics, grouped with the likes of paranormal research and the like.
Airline pilots are highly trained professionals; many were initially trained and flew for their respective Air Forces. Few are willing to risk their credentials by making public reports considered likely to embarrass the organizations for which they are working. The underlying perception of evoking an irrational fear in the flying public would further discourage major airlines from making any public announcements confirming reports by airline pilots sighting or encountering UFO's in flight. This position is likely to continue until irrefutable proof where a UFO visits plant and lands in a public place to once and for all end the continual debate, alleged government cover-ups and the overall perception that people reporting UFO encounters are one step short of full sanity.