This investigation missed the opportunity to investigate the difficulties of modern operations; the interactions between technology, ATC, and humans - work as imagined (SOPs) vs work as done.
The flaps were set to 30 (17:43:37) which is the ‘norm’ for most operations; the checklist was complete and called. Although a flap 40 landing was briefed it is a ‘non-normal’ config relating to the specific conditions; the error was detected and rectified before 500ft.
Although the choice of action just above 500ft was not ‘technically’ correct for IFR operations, there had been significant discussion about a visual approach. Also, what is the norm for this operator; are there routine late flap selections and transgressions of the rule. FDR/FOQA might not be able to differentiate between VFR and IFR; how can the operator management know what the everyday flap selection practice is?
The point about the HUD could be significant (chksix #11); not so much a systems disagreement, but different interpretations/use of the data and presentation.
How does the operator specify the HUD to be used for monitoring vs how it is actually used? Is the approach monitored with raw data (where the aircraft is/is going) or is the monitoring via the computed guidance symbol (what is required to achieve the idealised computed flight path).
In the latter case, and depending on the type of computation, reverting to the guidance at low level from an off ideal flight path might be hazardous.
During a HUD approach it is normal for the computer to fadeout the ILS GS with reducing altitude and substitute an averaged flight path or attitude, thus if the guidance is to be used for corrections at low altitude from an off-ideal flight path then a ‘maintain flightpath’ command might be expected, yet erroneously with a higher than normal descent rate.
What parameters was the Captain using as a monitor and then what for a landing reference after take over?
It is difficult to determine the descent rate from the HUD alone, particularly if the focus of attention is being transferred to the real world from the guidance symbol. Contrary to many beliefs it is difficult to comprehend both the HUD guidance and the real world simultaneously, and the changeover between the two is similar to that of head down (instruments) to head up (real world) where the time required to establish a meaningful understanding of the situation could be 2-4 secs … 20 to 40 ft.
Even if the investigation was not able to determine facts in these aspects they could have considered and reported on them, more so than the attendance on site or otherwise, or quoting ‘meaningless’ safety statistics.
A lost opportunity for safety learning.