Analysis of Uncorrelated Primary and Beacon Targets (JAL-1628)

This document consists of a memorandum from the Federal Aviation Administration (FAA) dated February 27, 1987, regarding the radar data associated with Japan Airlines flight 1628 on November 17, 1986. The memorandum serves to transmit an analysis of radar targets, specifically addressing what had been referred to as 'split images' or 'uncorrelated targets' in relation to an alleged UFO sighting reported by the flight crew. The FAA analysis, conducted by Dennis R. Simantel of ZAN-AAL-ARTCC, reviewed approximately 61 minutes of data extracted from the EARTS CDR printouts. The findings concluded that the radar data did not show any abnormalities associated with the pilot's report. Instead, the FAA experts determined that the 'uncorrelated primary and beacon target' phenomena occurred when the radar energy (primary signal) and the aircraft transponder (beacon) signal returned to the receiver at slightly different moments, causing them to appear in different range cells on the radar screen. The document includes technical explanations and diagrams illustrating how this timing discrepancy occurs within the radar equipment, specifically noting that such occurrences are not uncommon and are considered normal for the Murphy dome radar system. The FAA maintained that the controllers acted correctly by working with the information presented on their screens at the time, and that the data from the JAL-1628 flight was representative of normal radar performance in that area.