I have referred to this incident before, but have now found a link to the original article.
https://safety.army.mil/Portals/mult...es/ffmay98.pdf
Whilst the hypothesis of Air Marshals Day & Wratten "fits the known facts", so would this account of a near accident if applied to ZD576 from a starting altitude of 400-500 ft. The UFCM incident described is not conjectural; it happened and
could have been the cause of the Mull crash. I commend you all to read it.
Note: My Anti-Virus software warns that there may be a problem with the site's security certificate, though downloading the article doesn't appear to have caused any problem. If you are worried, Transport Canada has reproduced the article here (though I haven't checked that it is verbatim):
Aviation Safety Vortex 3/1998 - Transport Canada