The G550 is not auto land capable.
Instrument approaches are limited to CAT I visibility/ceiling. FYI: The EVS/HUD combination allows continuation of the instrument approach below CAT I DA to 100' above threshold elevation (TDZE), as long as certain conditions regarding the instrument approach and visual cues are satisfied.
In particular:
- approach is flown using HUD/EVS to CAT I DA
- before reaching CAT I DA, PF must be able to see runway approach lighting in the EVS - if so, the PF calls 'EVS lights - continuing to XXX feet'
- if EVS approach lights are not observed before CAT I DA, and PM does not observe runway environment, then 'Go Around' is called
- if runway approach lights are observed in the EVS and called, but runway environment is not observed at or before 100' above TDZE, then 'Go Around' is called
I truly hope that this was not a case of a crew deliberately aiming short/diving below the glideslope for some purpose... if so, the reasons why you shouldn't are all too evident in this case.
Another possibility is that the crew employed a non-standard procedure using the EVS, and with inadequate/misinterpreted visual cues misjudged their short final approach path.
No doubt there are many other possibilities...
Having said all of that: it remains for a BOI to determine what happened and ascertain causal factors, if one is convened. Should be some good lessons learnt, no doubt.