The photograph below was taken at midday on 29th August 1997 facing north, from south Bristol, England and shows what may be a contrail produced by a secret spy-plane referred to as the Aurora or sometimes the TR-3B. Unfortunately the photographer only saw the contrail after the airplane had passed out of view. Notice the regularly spaced donut-on-a-string effect which may be caused by an advanced pulsed detonation type of propulsion system. It is believed by some that the Aurora / TR-3B could account for a number of UFO sightings around the world, in particular the Flying Triangles (FTs).
In September 1999 a group of people on Tickaboo Peak (about 25 miles from the Groom Lake test facility in Nevada - also known as Area 51) observed a black triangular-shaped object taking off in daylight. This may have been the Aurora.