Originally Posted by flyingnewbie10
I will dare to post a preliminary comment about your why-because graph. My apologies If I say any nonsense:
Thank you very much for your comments.
1 - Factor 11 (assumption) could well be the one you pointed out (F/C did not expect autobrake not to operate) to explain F/C not commencing "Loss of Braking" procedure immediatelly. But if "Loss of Braking" implies using full manual braking (is it ?)
As much as you deem necessary. Since it is often an emergency situation, I would guess that it usually implies
full braking. (On less than optimal surface conditions brake performance will be limited by anti-skid anyway.)
I suppose it could also be explained by the fact that the crew at least thought that the runway was slippery and did not start using braking immediatelly to avoid an hydroplanning as the speed was still high;
I don't think so. As someone has pointed out, hydroplaning is independent of braking, it happens even with spinning wheels. (In driver-training one common exercise is to accelerate in (low) standing water and experience the onset of loss of control (steering) that happens at hydroplaning. Don't try this on public roads!) For all we know anti-skid was operative, so would prevent wheel-locking. (I have to admit I don't know if or how well it works during hydroplaning.)
The strongest argument, though, is that they had selected autobrake MED, which would commence braking 2s after MLG touchdown, even though they perhaps suspected the runway to be slippery and maybe anticipated some degree of hydroplaning.
I don't think it makes any sense to delay braking because one anticipates hydroplaning.
2 - Is there a way to have a more detailed description of factor 18 (Thrust Lock after A/THR disconnected) just to contemplate the fact that it worked exactly as designed and the "locked" thrust was within the range of the right TLA reading ?;
Since it worked as designed, I don't think there is a need for that. I may add an annotation that the locked thrust was well below the maximum allowed by A/THR operation.
3 - Does the graph accept multiple assumptions ? Could Factors 36 and 42 have parallel hypothesis ?
Not normally. The usualy way to deal with differing possible explanations for one event is to create a set of subgraphs for the event in question.
I have included the one (of many) hypothesis that I consider the most likely. Others may disagree, which is why I have marked the nodes as assumptions.
Both (6) and (36) have alternative explanations, and, of course, (42) also requires an explanation. Be it crew action, or a mechanical problem impeding free movement of the levers. After the final report is released, this may be amended.
The stopping rule in WBA, i. e. when to leave nodes as leaves, is variable and depends on the intended scope, the available information, and other factors. I have decided in this case that I have too little information to decide why (42) might have been the case.
Bernd