Zeffy, no criticism of your views on HUD. Your experience appears to be more recent than my dated exposure might be.
Re additional 1.5 deg 'air-mass' flight-path
Flying a stabilised approach on a ground referenced path (ILS GS) the aircraft maintains a constant rate of descent, e.g. in still air 148 kt, very approximately 750ft/min.
In a tailwind the stable rate of descent will increase - 163 kt Grnd Spd (-15kt wind), say 850ft/min.
To provide the higher rate of descent the attitude has to be more nose down – no difference between HUD / non HUD.
The ground reference flight-path remains the same, but if the flight path is referenced to the airmass (moving with you in a tailwind), then the airmass flight-path has to be steeper. My quick rule of thumb (approximate and varies with aircraft type), equates 10 kts to 1 deg.
So far (sorry - sucking eggs), this is probably of little practical value, other than to cue thoughts about the differences in a situation during a tailwind approach – but thinking about the differences is important.
The point of this observation is that in the HUD, the aircraft attitude reference will be much lower, perhaps unusually so (1:1 world relationship), such that the interpretation/unfamiliarity of this situation might require higher workload – it requires a plan – thinking ahead.
The offset LOC could be of greater concern. The approach was night/IMC; it is reported that the PF was using HUD (manual or monitoring autoflight?). During the approach the HUD FD would have been centered, however when visual and aligning with the runway centerline, the LOC component of the FD has to be ignored; the GS can still be used.
If the HUD symbol is a combined cue (circle/donut), then split axis flight can be very demanding. Also, there is a potentially confusing situation depending where the LOC axis crosses the runway centerline – threshold, or earlier at 200ft. The latter might result in flying through the centerline requiring a roll reversal. This too could increase workload, particularly in the shorter time scale than normal due to the tailwind – more bank angle required.
Considering the vertical; whilst the ILS GS could provide information, the optimum HUD mode might be visual / ground referenced approach path (as discussed previously). Changing modes (either manually or just mentally), IMHO requires great concentration.
The normal ‘every-day’ situation might be to transition from IMC to VMC without changing the way in which the HUD is used or the operating mode – the flare can be completed using the same display (FD) as for the approach.
However, with an offset LOC, even if the flare mode was working, part of the display has to be ignored. The main guidance symbol may not be aligned with the runway, presenting a different mental picture of the situation than the norm – a recipe for confusion, distraction, high workload.
Hence, in addressing a previous question ‘why didn’t the crew see the threshold / touchdown zone’, then the PF could be ‘maxed out’ flying the HUD, with little or no spare mental attention for updating the situation – and it was dark, heavy rain, and possibly poor lighting.
Of course, the above is supposition, IMHO justifiable, supported by the explanation of the difficulties of using HUD in a demanding situation.
Will these aspect be considered be in any formal report? I wait with interest.