Originally Posted by
Eclan
I'm not sure about windward/leeward as I don't know which direction the wind was from
Me neighter, but looking at the smoke column direction gently climbing up the slope, makes me believe the wrckage fell onto the windward side for sure.
Surface winds in the wider area (Sion, Milano) were weak, westerly or variable, so the likelihood of mountain wave activity is low.
Nevertheless, insolation of the easterly surface on such a clear day can produce powerful thermals by this time in the morning. Since the western / northern side of the pass is colder, this can cause a strong vertical gust over the pass. This might be a viable speculative scenario. why the wreckage fell onto the eastern side.
(Or CO poisoning.)