NVpilot, this is an excellent forum for sharing and respecting opinions.
In forming an opinion, I attempt to consider as many relevant circumstances as possible.
Perhaps your view and that of
Lemaurin previously, places too greater emphasis on normal (routine) operations, particularly in the context of this accident.
I hope that I have included relevant aspects of the situation where the crew may have been stressed by external or internal pressures, i.e. previous ATC exchanges, operational expectation, or a demanding landing on a short, wet runway. It is in these conditions that the weaknesses of systems – be they human, system interface, or procedure, have greater relevance; this is the context of my opinion.
Key factors in avoiding accidents, the human perceptions and behaviors, exist in normal operations. Every day we avoid or detect and correct errors, we perceive operating hazards and choose safe courses of action according to the situation. Somewhere, or somehow this process failed in this landing - ‘the crew thought it was a normal landing’.
You provide a caveat for this landing – ‘I would use manual braking’ – why? What perception (in hindsight), directs this course of action, what’s different about this situation that results in the ‘bending’ of you opinion of the value of auto brake?
Why is this runway any different to a contaminated runway, on which you would use less than the max braking available (an aspect where we have vastly differing opinions)?
May I suggest that just because the runways is short, wet, or requires a steep approach, it does not call for a change in the choice of braking; precision and promptness in flying and retarding actions, yes. However, if there are indications that the landing safety margins might be eroded (tailwind, slippery runway) then manual braking would be a good precaution.
IMHO manual braking provides an earlier indication that the runway friction may not be as expected, by having better sensing than with auto brake; in more extreme circumstances with auto brake and low experience of slippery conditions, low friction might not be detected until reverse is cancelled – too late.
A problem for the investigator is that the thinking activities of perception and choice are not self evident from the FDR or CVR, and even with a crew debrief, they are subject to hindsight bias.
In the context of this accident, the crew appear to have followed normal procedures (calls at touchdown and rollout), including 70 kts. The ‘normal’ habit would be to cancel reverse, but if the runway was judged to be slippery then the habit should be changed - non normal operation. The failure to change implies that the either crew did not perceive that the rollout was not progressing as expected, or that they realize something was wrong and chose an incorrect course of action; it is also possible that the runway friction decreased toward the end of the rollout – too late. The contributions and precursors to these situations are numerous and hidden in the depths of James Reason’s Swiss Cheese model or the ‘risks of organizational accidents’.
The view above assumes a slippery runway which some people have dismissed; I remain open minded. The runway charts are annotated ‘during rainy season, touchdown zones extremely slippery’; it was or had been raining. Reports of recent runway improvements may have improved the surface, but from other incident examples, new asphalt (and rain) can produce a very slippery greasy surface.
Although the runway has been assessed as safe after the accident, the details are not available; I also note that … “there is not, at present, a common friction index for all ground friction measuring devices. Hence it is not practicable at the present time to determine aeroplane performance on the basis of an internationally accepted friction index measured by ground friction devices”. CS 25 - AMC 25.1591
It may be very difficult to determine the significant contributing factors in this accident, but if as it appears that “in the Captain’s opinion” the attempt to land was safe, then the investigators might determine (in their opinion) some factors which show that the decision was imprudent or more likely the situation was not as expected.
But that’s just an opinion.
