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This FAA release, dated February and March 1987, covers the radar data from Japan Airlines flight 1628 on November 17, 1986. It includes a statement and drawing by Paul Steucke of FAA Public Affairs in Anchorage, a memo from the Airway Facilities Division, and an analysis by Dennis Simantel. They conclude that the radar showed an uncorrelated primary and beacon target, which they describe as a normal timing effect and not an unknown object.
I I ~ ,..J H ~ '1' -- UNCORRELATED RADAR SIGNALS An "uncorrelated primary and beacon(secondary) return on a radar screen occurs when the radar energy that is sent up toward the aircraft (primary signal) returns off the surface of the aircraft at a slightly different moment than tbe beacon (secondary) transponder signal and the two do not match up as being at the same place or same computer radar cell. --RADAR COMPUTER CELL, 1/4 MILE-- SECONDARY RADAR RETURN (Beacon) (Transponder) --1! FAA RADAR SAME AIRCRAFT (Skin- Surf ace) --//'- RADAR CELL =PRIMARY RAD~ RETURN =SECONDARY RADAR RETURN =CORRELATED RETURN (Combined Return) Drawing by Paul Steucke March 5, 1987 =UNCORRELATED RETURN
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