Summing up the answers to some recurrent ideas, and also some (seemingly) new ones.
1/
Mr. Spaz "outagaz" Modic
L337, regarding Spaz Modic, I might just say, "Please don't feed the Troll".
But in addition to what the AAIB report says about fuel on board, see the very good and insightful discussions (in particular Green-Dot's post #878 from April 14, thanks a lot for that!) on frost on the wing underside, and its relation to fuel levels in the main (wing) tanks.
Unless you're a diehard conspiracy theorist, this shows convincingly that the figure of just above 10 tons mentioned in the report is about right.
2/
AD 2008-02-05 and Core Icing
a-
Timing
The release of said AD in temporal proximity to the accident we're discussing is coincidental. It deals with extended (in this case: more than 45 or 60 minutes) ground operations in freezing fog of low visibility. Said release is to reduce the threshold distance from 1000 to 300 metres visibility for the described procedures.
b-
Conditions relevant to the AD
BA038 didn't perform extended ground operations in freezing fog.
What is the typical time, including a 5-minute hold, from TOD to touchdown for a flight on this route? I have no idea, but I guess it will be less than 45 minutes, a considerable time of which will be spent outside freezing fog, and above idle thrust.
Even if clouds in cold temperatures (AD talks about the three distinct cases of 0 to -6 C, -7 to -13C, and below -13C) could be called "freezing fog", BA038 will not have spent anywhere near 45 minutes inside them at near idle thrust. More to the point, takeoff in the conditions described in the AD is even permitted after up to 60 minutes without intermediate run-ups, i. e. engine damage leading to immediate failure is not expected by the ice accreted within that time, although slight engine damage may occur, so an inspection within 10 flights is mandated.
c-
Core Icing
We cannot yet exclude core icing as a causal factor in this accident, but the dangers of core icing as described in AD 2008-02-05 are engine shutdown and/or engine damage when accreted ice chunks above a certain size brake loose. For BA038 we are not talking about a shutdown, but merely a reduction in thrust. It may be related, but we don't know yet.
3/
Fuel flow
The AAIB report states that the fuel flow reduced, first in one, and then in the other engine. It also states that the EECs responded correctly by opening the fuel metering valve. Actual fuel flow is measured after the metering valve, and we can be quite certain that the AAIB would have mentioned an increase in fuel flow caused by opening the metering valves, which was not accompanied by a corresponding increase in thrust.
Regarding ideas about a full flow rate of a liquid with just not enough energy content: I find it hard to believe that a liquid with an energy content just enough to deliver slightly above idle thrust at maximum possible flow would burn at all. We're talking about a fully open metering valve, which would, given normal fuel, equate to above TOGA thrust (TOGA will not be the limit of what the fuel system can deliver, but a limit imposed by the software in order not to damage the engine).
Fuel (or rather: energy) flow needed for thrust slightly above idle is only a small fraction of the total fuel delivery system capability. All fossil fuels have roughly similar energy contents, so the largest percentage of the liquid delivered in this scenario would have to be something uncombustible, dare I say water? Would a liquid of mostly water be able to sustain combustion?
Wouldn't it also leave highly supicious traces in the fuel lines, bound to be found by the investigators? How does that reconcile with the AAIB's stating that ...
Originally Posted by AAIB-Report
[...]
there were no signs of contamination or unusual levels of
water content. A sump sample taken from the left and
right main fuel tanks shortly after the accident revealed
no significant quantities of water.
There are (or were) a couple of fuel chemists and other professionals of the field in the thread, I'd like to hear their view on this.
d-
Hesitation
Maybe I have a strange book, but in all the dictionaries "to hesitate" means to "pause before doing something". Some add "uncertainty" as a reason for this kind of pausing. I cannot see anything in this accident that would fit that definition. A thrust increase was demanded, fuel flow and thrust increased (without any mention of a delay, or "hesitation"), and then fuel flow and thrust reduced, despite further increased demand, and stayed at that low level.
So you might say it "hesitated" to reduce thrust uncommanded. I don't think that would be a useful description.
Cheers,
Bernd