Optical and Radar Analyses of Field Cases
Gordon O. Thayer
Case 21.
Colorado Springs, Colo., 13 May 1967, 1540 LST (1640 MDT). Weather:
overcast, cold, scattered showers and snow showers (graupel) in area,
winds northerly about 30 mph., gusts to 40 mph., visibility air -- more
than 15 mi. (Colorado Springs airport is not horizon-limited;
visibilities of 100 mi. are routinely reported on clear days). This is
a radar-only case, and is of particular interest because the UFO could
not be seen, when there was every indication that it should have been
seen.(See Section IV).
From the time the UFO was first picked up on radar to
the time the Braniff flight touched down on runway 35, the UFO track
behaved like a ghost echo, perhaps a ground return being reflected from
the aircraft. This is indicated by the fact that the UFO blip appeared
at about twice the range of the Braniff blip, and on the same azimuth,
although the elevation angle appears to have been different. When
Braniff touched down, however, the situation changed radically. The UFO
blip pulled to the right (east) and passed over the airport at an
indicated height of about 200 ft. As pointed out by the FAA, this is
precisely the correct procedure for an overtaking aircraft, or one
which is practicing an ILS approach but does not actually intend to
touch down. Although the UFO track passed within 1.5 mi. of the control
tower, and the personnel there were alerted to the situation, the UFO
was not visible, even through binoculars. A continental Airlines
flight, which was monitored 3-4 mi. behind the UFO at first contact,
and was flying in the same direction, never saw it either.
Both the PAR and ASR radar transmitting antennas are
located to the east of runway 35, and they are about 1,000 ft. apart on
a SW-NE line. A ghost echo seems to be ruled out by at least the
following considerations:
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- A ghost echo, either direct or indirect,
normally will not be indicated at a height of 200 ft. while the
ghost-producer is on the ground, as was the case here;
- A direct ghost is always at the same azimuth as the
moving target, and an indirect ghost is on the same azimuth as the
fixed reflector involved. (See Section VI Chapter 5). If an indirect
ghost were involved here, the ghost echo would thus have always
appeared well to the east of Braniff, not at the same azimuth.
The radar flight characteristics of the UFO in this
case were all compatible with the hypothesis that the unknown was a
century-series jet (F100, F104, etc.), yet nothing was ever seen or
heard.
This must remain as one of the most puzzling radar
cases on record, and no conclusion is possible at this time. It seems
inconceivable that an anomalous propagation echo would behave in the
manner described, particularly with respect to the reported altitude
changes, even if AP had been likely at the time. In view of the
meteorological situation, it would seem that AP was rather unlikely.
Besides, what is the probability that an AP return would appear only
once, and at that time appear to execute a perfect practice ILS
approach?
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