Originally Posted by
Mark1234
So, say for the sake of arguament, one is wallying along just under someone's controlled airspace, and elects drop mode C, and goes mode A only, what impact does that have on those controlling the airspace - do they just 'assume' you're outside vertically unless proven otherwise?
Mark,
I see from your details you are based in Oz and my answer is related to UK and US.
First, you will frustrate the controller who will have yet another no altitude target (and maybe be illegal if in the US). If the controller notices you were Mode-C and now are Mode-A, I would guess he will then treat your target with care, assuming either you have a problem or you think you are lost/infringing and don't want to be caught.
You then become an irritation to everyone with a TCAS/TAS or similar system who still know of your existence but have no clue where you are vertically, finally you get a place in the Cussed Poor Airmanship list for being deliberately awkward.