Originally Posted by
Landroger
I joined this forum because the circumstances of BA038 were, to this uninvolved bystander engineer, quite simply; staggering.
You aren't the only one.
Unbelievable. And yet today the report uses the word 'probably'.
That shouldn't be a surprise, it wasn't to me. Since the early interim reports it's been made clear that there was some sort of obstruction in the fuel system, that disappeared before investigation. Ice / wax / slush typically doesn't stick around to be investigated, and can form and behave "randomly" making reproducible experiments practically impossible.
Realistically, "probably" was always as close as we were going to get.
However, unless I've missed some big numbers somewhere, it seems quite extraodinary that so little water could choke such big engines at such a critical moment in the flight.
What you may have missed is that the suspect is not water ice, in fact I think the AAIB may have confused many by referring to it throughout as "ice". It is actually a slush made up of fuel and water, at above the waxing point of the fuel but below the freezing point of water. It isn't clear that this is a previously known phenomenon - it isn't a well researched state of fuel, if it was known about at all.
The reported tests showed both that a spoonful of water could create enough of this "ice" to block the FOHE, and that larger quantities of this "ice" (more than enough) could acrete on pipework over time at low fuel flow rates.
Since entrained water and ice in fuel systems has been endemic all through the history of high altitude, high speed flight and certainly during the whole operating career of the 777 - a lovely aeroplane to my mind - why hasn't it happend before?
AAIB: "Data mining showed that the accident flight was unique amongst 175,000 flights..."
That was a big data excercise, and found no other comparable flights, so we have no idea how many flights you would need before you would be likely to see a repeat of these circumstances. Quite possibly more than the total 777 flights to date.
Perhaps it has been decided to apply the principle of Occam's Razor and accept that ice is 'probably' the cause.
To apply Occams Razor, you need to have other hypotheses
that also fit the evidence. I see none. Up to now I would have said that the spar-valves were still a suspect on the info we had, but I believe I see in this report the evidence on which the AAIB have ruled that out (not as clearly presented as I would like, but I think it is there).
What I do see in this report, in much more detail than we had before, is lots of elimination of other hypotheses before ending up with the "ice" as (only) probable cause, ie.
"When you have eliminated the impossible...". That isn't Occams Razor - in fact it is more the reverse of it.