Simulated radar data, black-and-white

ANALYSIS OF UNCORRELATED PRIMARY
AND BEACON TARGETS
(JAL-1628, 11/17/86 AKST)
Approximately 61 minutes of data was extracted from the EARTS CDR
printouts relating to the November 18 incident involving JAL-1628
and the alleged UFO sighting.
Review of the data involving this incident did not show any
abnormalities that could be associated with any type of target as
indicated by the pilot · of JAL-1628.
Radar returns from the aircraft and surrounding terrain vary with
the different segments of the flight, but are considered normal
for the area.
Returns relating to the incident can be categorized as three
types: primary radar reinforced by a beacon reply (primary radar
returns and beacon returns are both evident in the same 1/4 mile
range cell), beacon only reply and beacon with an associated
radar reply. Seventy-two percent of the replies were radar with
beacon reinforcement (same range cell) which is normal for the
Murphy dome radar system.
Approximately 25 percent were beacon only and of those that
registered as beacon only, 90 percent of those had a primary only
reply within 1/8 of a mile, either ahead or behind the beacon
target (..&"behind, -1:-2"' ahead) .
~ ~/3/B 7 ~ 13
These uncorrelated primary returns are not uncommon, due to the
critical timing associated with the delay adjustments in the
aircraft transponder for beacon systems and the target
correlation circuitry within the radar equipment.
When an aircraft is being interrogated as it passes through the
beginning of adjacent range cells the intricate timing between
the two systems very often is off just enough to declare both a
beacon and a radar target in different range cells, resulting in
uncorrelated radar replies.
The data derived from the JAL-1628 flight is representative of
the data from another aircraft in the same general area and is
considered normal.
February 25, 1987
-us .T5ennis R. Simantel
ZAN-AAL-ARTCC
)
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