MadMax9,
Many thanks for taking the trouble to post a range / time analysis. However, I suspect that the peak which is 450 pixels to the right of Piz Aul in the panoramic image... is actually Piz Terri, and not Piz Mendel. The latter is much further away, and by my reckoning from the map should appear close to a cable-car pylon on the ridge... not the previously-mentioned one (post #168), but the one which stands to the right of the wooden post… even allowing for ±100m uncertainty in the actual camera position. (Also, if you do an internet search for Piz Terri, there is an excellent summit photo taken from a slightly more southerly position, which can be matched well to the summit which appears in the panoramic image.)
As the bearing from the panoramic camera to Piz Terri is closer to the bearing to Piz Aul (than is the bearing you have proposed to Piz Mendel), then that would place the aircraft further away.
In any case, a safer analysis (avoiding any debate about summits!) might be to note that the full 360° panoramic image width is covered by 15707 pixels, making 0.0229° per pixel. Taking the aircraft width as 4 pixels, and assuming that the aircraft is approaching the camera (I agree with you that the lack of height or asymmetry in the dark pixel distribution supports this orientation), then a 30m wingspan would subtend 4 pixels at a range of around 18.7km (or 15km if the wingspan is taken as being spread over 5 pixels). This would then place the aircraft over (or slightly beyond) the Piz Mundaun feature, i.e. about 5km SW of the town of Ilanz.
Also, I suspect that 180km/hr as a groundspeed might be a bit optimistic for these aircraft – particularly on a leisurely sight-seeing flight, the appeal of which would surely be more about the flight than a timely arrival. (Indeed, when I see them flying past my house, their progress is usually – shall we say – somewhat unhurried!) So, if the dark pixels are indeed the JU52 around Piz Mundaun, then it could perhaps be 7 to 8 minutes after the image was captured, before it reached the Segnespass area.