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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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However, if the signal was coming from the Duncanville radar the displayed bearing should have been approximately $ 3 5^{\circ} $ , whereas the bearing reported by McClure and listed in the Piwetz account is $ 7 0^{\circ} $ . But as earlier noted, all bearings are measured relative to the airplane fore-aft axis so that if the RB-47 were maneuvering at the time this would introduce a discrepancy. Since there is no way to know for certain whether the aircraft was in level or maneuvering flight at that moment, it will be useful to examine subsequent ALA-6 bearing measurements and compare them with the expected values to determine if the S-band signal was coming from the Duncanville radar.
Figure 6 (p.11) is a careful plot of the calculated RB-47 flight path, developed with the assistance of aircraft commander Chase, showing all reported bearings of the unknown S-band signal, so the reader can compare them with the actual bearing to the Duncanville radar. All times/events are based on the Piwetz report, unless otherwise noted.
At 10:352, McClure reported the S-band signal to be at a relative bearing of $ 6 8^{\circ} $ From my calculated RB-47 flight path, assuming the airplane in level flight, the bearing to Duncanville would be roughly $ 4 0^{\circ} $
At 10:38Z, the S-band signal bearing was approximately $ 4 0^{\circ} $ . The bearing to the Duncanville radar would be roughly $ 4 5^{\circ} $ .
At 10:39Z, the aircraft commander "sighted a huge light which he estimated to be 5,000 feet below aircraft at about 2 o'clock. [Piwetz account.] Aircraft altitude was 34,500 feet, weather perfectly clear. Although aircraft commander could not determine shape or size of object, he had a definite impression light emanated from top of object." [NOTE: This was the first visual sighting since 10:10Z, and did not occur until nine minutes after McClure acquired S-band signal.]
At 10:40Z, McClure "reported he then had two signals at relative bearings of 40 $ ^{\circ} $ and 70 $ ^{\circ} $ ." Based on calculated RB-47 position, the bearing to the Duncanville radar would have been roughly 50 $ ^{\circ} $ . Piwetz account states: "aircraft commander and co-pilot saw these two objects at the same time with same red-color." However, Chase recently told me that he does not recall ever seeing two visual objects.
If the S-band signal was coming from a UFO, then the craft apparently had divided into two widely separated objects! A more plausible explanation is suggested by the ALA-6 Handbook of Operating Instructions IF the signal was coming from the Duncanville radar. The handbook says that the ALA-6 may at times display what appears to be TWO SIGNALS AT TWO DIFFERENT BEARING ANGLES (from a single radar) "due to a reflection from some nearby object to the left of the true signal reflection." This condition is illustrated in Fig. 5, using a photograph from the ALA-6 handbook.
Shortly after 10:40Z, the RB-47 commander obtained permission from the Civil Aeronautics Administration to deviate from the original flight plan to pursue the UFO.
The RB-47 then turned right, to a heading of $ 3 2 0^{\circ} $ , putting it on a path that would take it toward Dallas-Ft. Worth. [See Fig. 6, p. 11.] The RB-47 contacted the Duncanville radar station (Code Name: "Utah") and "requested all assistance possible," in its UFO chase, according to the Piwetz account.
At 10:42Z, only a single S-band signal was noted by McClure, having a bearing of $ 2 0^{\circ}. $ From the RB-47 calculated flight path, the bearing to the Duncanville radar also Document, cited by the archive. The PDF is mirrored here; the original link is above. The text was read from the page images by GLM-OCR; expect the odd misread word. 57 pages are in the text index: search them above, or from the library's search.