SQ-368 (engine & wing on fire) final report out
Source of fuel leak/fire identified, not a word on the (lack of) evacuation.
AAIB’s investigation is on-going and we will be looking into other aspects of this incident that may have safety implications.
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Hi folks,
I do have a query as am unable to understand ( without a detailed drawing of the lub oil system for the engine ) how a leak in the main fuel oil heat exchanger can cause a fire. Would the initial oil leakage not be into the fuel system and burnt in the combustors ( am assuming that the oil pressure is higher than the fuel pressure in the heat exchanger)?. This would then lead to a drop in oil pressure ;until fuel eventually enters the lub oil system and ultimately damaging the engine bearings. As the lub oil system is a closed one, how does fuel leak out of a closed- system to cause a fire,unless a fuel line or the heat exchanger body is also breached ?
Am sorry to be ignorant on such matters and will highly appreciate comments and thoughts on this , to help me understand.
Thank you
Cheers
I do have a query as am unable to understand ( without a detailed drawing of the lub oil system for the engine ) how a leak in the main fuel oil heat exchanger can cause a fire. Would the initial oil leakage not be into the fuel system and burnt in the combustors ( am assuming that the oil pressure is higher than the fuel pressure in the heat exchanger)?. This would then lead to a drop in oil pressure ;until fuel eventually enters the lub oil system and ultimately damaging the engine bearings. As the lub oil system is a closed one, how does fuel leak out of a closed- system to cause a fire,unless a fuel line or the heat exchanger body is also breached ?
Am sorry to be ignorant on such matters and will highly appreciate comments and thoughts on this , to help me understand.
Thank you
Cheers
Aviator, two possibilities:
The failure in the heat exchange extended to the housing - allowing fuel to not only get into the oil system but to also leak overboard;
So much fuel got into the oil system that it overfilled the system and started going overboard out the vents and breathers. Or perhaps a combination of the two.
I suspect the fuel leak was relatively small - with the throttle pulled back to idle on that engine and the opposite burning at max con, the other engine was still burning much more fuel than the event engine was burning and leaking. So the fuel quantity on the side with the leak would still be considerably higher - diagnosing a leak under those circumstances would be difficult.
The 777 does have an alert if the FQIS and the total fuel burn don't agree, but it has a big tolerance (several thousand pounds) to avoid nuisance alerts.
Thanks etudiant - even a blind hog finds the occasional acorn
The failure in the heat exchange extended to the housing - allowing fuel to not only get into the oil system but to also leak overboard;
So much fuel got into the oil system that it overfilled the system and started going overboard out the vents and breathers. Or perhaps a combination of the two.
I suspect the fuel leak was relatively small - with the throttle pulled back to idle on that engine and the opposite burning at max con, the other engine was still burning much more fuel than the event engine was burning and leaking. So the fuel quantity on the side with the leak would still be considerably higher - diagnosing a leak under those circumstances would be difficult.
The 777 does have an alert if the FQIS and the total fuel burn don't agree, but it has a big tolerance (several thousand pounds) to avoid nuisance alerts.
Thanks etudiant - even a blind hog finds the occasional acorn
Interesting that the Preliminary Report earnestly recommends actions to Boeing, GE and the FAA while no mention whatsoever is made of ground events post landing.
Perhaps in the AAIB's thinking that once the wheels have stopped, the flight is over and there is no remit to investigate subsequent events
Perhaps in the AAIB's thinking that once the wheels have stopped, the flight is over and there is no remit to investigate subsequent events
Nemo Me Impune Lacessit
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In keeping with just about every other airline in the world, SIA will issue information which may effect other operators safety.
To evacuate or not is a domestic matter and will be dealt with as such, like every other airline in the world. Should an additional authority see fit to conduct its own investigation then you may get a report made public.
To evacuate or not is a domestic matter and will be dealt with as such, like every other airline in the world. Should an additional authority see fit to conduct its own investigation then you may get a report made public.
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Originally Posted by tdracer
( Possibilities) The failure in the heat exchange extended to the housing - allowing fuel to not only get into the oil system but to also leak overboard;
So much fuel got into the oil system that it overfilled the system and started going overboard out the vents and breathers. Or perhaps a combination of the two.
So much fuel got into the oil system that it overfilled the system and started going overboard out the vents and breathers. Or perhaps a combination of the two.
From my limited experience, nacelle leaks generally go overboard in the secondary engine airflow if they do not start a fire.
I'm expecting some sort of AD to come out of this. Fuel leaking from a fuel-oil cooler should never end up soaking the wing structure.
Last edited by Machinbird; 2nd Aug 2016 at 21:54. Reason: To better indicate TD racer's comments were conjecture.
Machinbird, purely speculation on my part (although I found the first acorn 
), but the oil tank is on the upper portion of the fan cowl. If fuel was entering the oil system at a high rate it has to go somewhere, so it's going to be forced out of the oil system somewhere. Out the oil tank vent/breather system is a likely exit point. By design, the fan cowl is well ventilated, so fuel in that area could get readily swept onto the surrounding underside area of the wing. The aircraft landed right about dawn, meaning it was dark for most of the flight - unlikely that anyone would notice fuel venting out of the fan cowl.
Also, depending on the leakage rate, the drain system could have been overwhelmed - especially since the drain system tends to accumulate debris if it's not cleaned out.
It's also possible that most/all of that fuel that was burning on the wing was blown up there when the reverser was deployed. It doesn't take much fuel to make an impressive fire (I think I saw somewhere that the BA 777 in Las Vegas only involved about 10-15 gallons of fuel).
), but the oil tank is on the upper portion of the fan cowl. If fuel was entering the oil system at a high rate it has to go somewhere, so it's going to be forced out of the oil system somewhere. Out the oil tank vent/breather system is a likely exit point. By design, the fan cowl is well ventilated, so fuel in that area could get readily swept onto the surrounding underside area of the wing. The aircraft landed right about dawn, meaning it was dark for most of the flight - unlikely that anyone would notice fuel venting out of the fan cowl.Also, depending on the leakage rate, the drain system could have been overwhelmed - especially since the drain system tends to accumulate debris if it's not cleaned out.
It's also possible that most/all of that fuel that was burning on the wing was blown up there when the reverser was deployed. It doesn't take much fuel to make an impressive fire (I think I saw somewhere that the BA 777 in Las Vegas only involved about 10-15 gallons of fuel).
Well from the recent posts above (Machinbird & tdtracer)
It would seem that the design of the engine installation does not preclude similar repeats from what was presumed to be a minor malfunction.
I wonder what regulation is going to have to address a beefing up in short order??
It would seem that the design of the engine installation does not preclude similar repeats from what was presumed to be a minor malfunction.
I wonder what regulation is going to have to address a beefing up in short order??
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Vapour pressure of avo vs oil
One has to remember that the engine lube system runs hot. This is the point of the heat exchanger in the first place - to cool the lube oil and pre-heat the fuel.
If the lube oil is contaminated with avo, or worse, replaced by avo, then the pressure in the lube system massively increases due to its much higher VP. Venting would be increased, as would the possibility of further leaks forming elsewhere. High oil pressure is an indication of possible leak of fuel into the lube system.
And now some questions. Do we know if the captain deployed the thrust reverser on #2? Why would he do that on an engine set to idle? Or might he even have deployed the reverser and applied some level of thrust to #2? The latter action might well make thing worse of course....
The absence of comment on the post landing events is noted. They do hint at further investigations at least. I suspect they want to put some time between the accident and having to say the lack of evac was not in the best interests of the pax and crew....
If the lube oil is contaminated with avo, or worse, replaced by avo, then the pressure in the lube system massively increases due to its much higher VP. Venting would be increased, as would the possibility of further leaks forming elsewhere. High oil pressure is an indication of possible leak of fuel into the lube system.
And now some questions. Do we know if the captain deployed the thrust reverser on #2? Why would he do that on an engine set to idle? Or might he even have deployed the reverser and applied some level of thrust to #2? The latter action might well make thing worse of course....
The absence of comment on the post landing events is noted. They do hint at further investigations at least. I suspect they want to put some time between the accident and having to say the lack of evac was not in the best interests of the pax and crew....
Do we know if the captain deployed the thrust reverser on #2? Why would he do that on an engine set to idle?
Buzz, if you suspect a fuel leak in or around the Engine ( which they did ) SOP requires Reverse thrust NOT TO BE USED as it can spread or spray the fuel all around the inside of the Engine cowling and it can ignite..............
So, they should not have even selected idle reverse at all on that Engine....
So, they should not have even selected idle reverse at all on that Engine....
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Exactly why I asked the question...
Buzz, if you suspect a fuel leak in or around the Engine ( which they did ) SOP requires Reverse thrust NOT TO BE USED as it can spread or spray the fuel all around the inside of the Engine cowling and it can ignite..............
So, they should not have even selected idle reverse at all on that Engine....
Ok.
So, they should not have even selected idle reverse at all on that Engine....
Ok.
In this case, they had no fire before landing (and perhaps, no suspected fuel leak). But they had already pulled #2 to idle. In that situation, I would not have deployed the bucket on #2, even on idle (little to be gained), and I would certainly not have risked applying reverse thrust for real. If the engine wasn't flight worthy, it also wasn't up to reverse on landing!
Alas the videos only show the last few seconds of roll out, so we are none the wiser...
Last edited by Julio747; 3rd Aug 2016 at 14:30. Reason: Correct typos
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Very good if everything is fine...
I don't know if he did but the normal procedure is to select both engines to idle reverse after touchdown, then apply reverse thrust as required during the landing roll. Selecting both engines to idle reverse kills any forward thrust from the engines after touchdown and helps with the stopping performance.
if you suspect a fuel leak in or around the Engine ( which they did ) SOP requires Reverse thrust NOT TO BE USED
I've yet to see anything that suggests the crew suspected a fuel leak - there's nothing to that effect in the 21.3 report or the preliminary accident report.
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Agreed.
But having pulled the #2 engine to idle 2 hours earlier, because it obviously had problems, would you use it for powered reverse on landing? I am not saying they did. We don't know. I am saying that to do so would be unwise in my view.
I guess at least one pilot will be looking for a job after this. Why? The Captain of the B777 accident aircraft at LHR, was out of a job for a while. He applied to "the Emirates" and was turned down because he had been involved in an aircraft accident.