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This Project Blue Book file, released through The Black Vault, covers the RB-47 encounter of 17 July 1957 over Mississippi, Louisiana, Texas and Oklahoma. It includes the record card, which lists the sighting as identified as American Airlines flight 655, and Air Defense Command correspondence that carried the sighting as unknown. There is also Major Lewis D. Chase's observer data sheet and an electronic analysis finding it difficult to conclude nothing was present. James McDonald's reconstructed account is included, along with a CAA letter about airliner incidents.
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McClure decided that there must be a malfunction in his ALA-6, but he did not report it to the aircraft commander at the time. (It was not until later, following the visual sighting of a luminous object by the pilot/co-pilot that McClure realized that the unusual up-scope movement could result from an airborne signal source passing the RB-47 at greater than the RB-47's 500 mph speed.) Analysis of the circuit diagram from the ALA-6 instruction books suggests several possible malfunctions that could cause an anomalous up-scope movement, one of which will be considered here. As previously noted, the AS-656 antenna assembly installed on the RB-47 employs TWO back-back dishes. One of these is selected when the ground radar signal is horizontally polarized, while the other is used when the signal is vertically polarized. Only one antenna dish is used at any instant. The ALA-6 operator selects the proper antenna dish by means of a toggle switch on the front of the ALA-6 control panel. If the operator lacks apriori knowledge of the radar signal polarization, he toggles back/forth and selects the dish which gives the optimum signal. When the switch is thrown to the "Vertical" position [See Fig. 3 below], it applies +28 volts to relay K-701, which then connects the vertically polarized dish to the APR-9 Elint receiver. When the toggle switch is thrown to the "Horizontal" position, it removes the +28 volts from relay K-701 and the spring-loaded relay then connects the horizontally polarized dish to the APR-9 receiver. When selecting the appropriate antenna dish, it is also necessary that the correct polarity of APR-9 signal be applied as excitation to the synchro-resolver rotor
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