NigelonDraft
Thanks, that's the most sensible post on the subject so far.
It's impossible to be 100% safe when flying outside of CAS (or within it to be honest).
Inkjet: I understand your point but...i spend most of my working day hand flying ILS calibrations without the autopilot in, without the flight-director and in VFR conditions. That's exactly what (i understand) the 402 was doing.
Ultimately, when calibrating we're flying visual approaches (with all that it entails) and NOT flying a precision instrument approach. We can't fly precision instrument approaches when the engineers are deliberately mis-aligning the LOC or GS in order to check the Alarms etc etc.
So, in this case, you'll find that both aircraft were (in all probability) flying visual approaches and the supposed protection of flying an ILS was not required.
Whether traffic information was passed by ATC to the 2 aircraft involved remains to be seen.
In the end it's a horrific accident that comes down to "see and be seen" not working. Only TCAS and transponding aircraft might have saved the situation.