A technical glitch somewhere along the line meant that two comments by Martin Shough didn't arrive at the Blog. I therefore reproduce them below, by re-typing from emails from Martin.
Thanks for posting this interesting follow-up. It's a pity that it was left to you to do this job now when ideally it would have been done 40 years ago, as you say.
If I could just comment on the comments:
Yes it would be very interesting to see radiosonde profiles for that day. I wish you luck in getting hold of them. Hopefully your request will focus if possible on balloon localities to the NW of the sighting area, in the sighting direction, which could be more significant than conditions in the immediate vicinity of the plane because the ray paths might be passing for long distances through an hypothetical optical duct extending over a wide area far from the plane.
Connected with that, I'd point out that the (equally hypothetical) target(s) of this mirage - silhouetted peaks, or clouds etc -might conceivably lie at a distance of hundreds of miles from the plane, so the topography and weather of the immediate Zanthus area is possibly not so relevant.
Note a point made in my report on the Captain Howard case (possibly notes 83, or thereby 11RC) - that the radio signal loss during the Zanthus sighting could be consistent with a strong temperature inversion causing an optical duct. In dry air such as might be the situation at altitude in reportedly very clear blue skies over a region like this, radio and optical ducting onset would be much closer in time than would typically be the case (radio wavelengths normally being affected disproportionately by the relative humidity.) It could happen that radio waves were being refracted and prevented from entering the optical duct. When the duct broke down, or the plane emerged from it, radio and optical propagation might return almost simultaneously to normal.
Re Captain Gardin's late recollections of details which indicate vertical angular displacements that seems to possibly conflict with a mirage explanation - the 45 degree final ascent, and merging of the satellite objects from underneath - I am reluctant to place as much weight on material information recalled 43 years later that was not mentioned at the time. Capt Smith's account (I agree with you) did give the impression - not explicitly, but by (I would say) conspicuous omission - that observed motions were confined to a horizontal plane.
It may not be irrelevant that these new details tend to increase the strangeness of the event. No doubt Gardin encountered attempts by various people to explain the sighting - possibly including mirage-type theories, of which the original story was at least somewhat suggestive, it would be natural to want to defend a contrary opinion in which the witness may have invested some public and personal capital over the years (as possibly also hinted at by the 'psychic' revelations.) A similar temptation appears to have influenced Captain Howard (BOAC case 1954) in similar circumstances a decade or more after the event, as proven by detailed documentary evidence in my report on that case.
In respect of memory, I note that Captain Gardin now recalls that "the Sun was above the horizon" and sky conditions in the sighting direction was "clear blue sky." However your own findings are as follows.
'A check of the astronomical sky using a software program indicated that at 0940 GMT (1740 local) the Sun had set and was about 4 degrees below the ground horizon, some 20 degrees to the right of the aircraft's track.'
I look forward to your further work on this interesting case. Perhaps contemporary evidence will emerge that convincingly disproves the mirage theory."
Second comment on the finding of a contemporary newspaper clipping.
"Thanks for sharing this discovery. As usual with newspaper reporters we have to be cautious about the account. It quotes Smith: "He said that a big white object had flown on a collision course with their Piper Navijo (sic) aircraft for 20 minutes" but if we are to credit Smith's own words in his own report of the RAAF file, this is utter garbage. The object(s) was/were not white, but dark grey or black. The objects were not at any time on a collision course, but on an apparent pacing course maintaining station. And the sighting lasted not 20 minutes, but 10 minutes. Not exactly ace journalism!"