Light Aircraft Association

Just doing battle with a mod 3 form - what a farce!

What exactly is an
Accompanying document supporting airworthiness of modification?

My grasp of the English language and aircraft matters is usually pretty good but this phrase conveys absolutely nothing.

My assumption would be to provide evidence that the modification still complies with the certification (e.g. CS-VLA). The flow chart does say "as requested", so I would guess you will need to have feedback from Engineersing after you have submitted your Mod 2 form?