SK8TRBOI The airmass flight path aspect may be an old view of HUD and not applicable to the newer systems – an irrelevancy.
It may be clearer just to state that in a tailwind, because the aircraft is going faster, the nose has to be lower in order to maintain the ILS GS, this gives a higher rate of descent. Although this is stating the obvious, these aspects have to be deduced from HUD symbols – not identical to conventional instruments. Thus there may be a higher workload when using HUD.
HUDs do not take ‘all of that’ into account. They can display much more information, and in differing formats to ADIs. If this information is not managed - workload / self discipline / planning, then in stressful or time critical situations the pilot may have less capability to attend to other aspects of flight.
The LOC issue may be clearer by considering an attempted head-down landing using a conventional flight director with a flare mode. With the LOC aligned with the runway the task is to keep the FD centred.
With an offset LOC the lateral guidance cue has to be ignored whilst flaring in pitch.
A split cue FD (cross wires) may be an easier task than with a single cue (combined pitch/roll) FD, many HUDs have combined cue FDs. This could be a demanding mental task which increases workload and decreases the ability to focus attention elsewhere.
Thus possibly as a result of routine HUD use for landing (straight-in ILS), crews are becoming ‘technology dependent’; it may be very difficult to break this normal habit – flaring with HUD FD, if the ILS is not straight-in. Combine this change in task with poor weather and low visibility, and a tailwind, these aspects could contribute to tunnel vision – HUD fixation.
I would argue that crews have to think out these issues in advance, particularly when using HUD in uncommon situations, and focus their risk assessment on adverse combinations of landing factors so that an alternative landing option can be selected.