Posts about: "AAIB (All)" [Posts: 151 Pages: 8]

Originally Posted by za9ra22

What configuration, specifically?

Caused by what? /
Didn't I read somewhere in the wiki, that the engines will continue to suck fuel? / Which is?
Contaminated with what, and how? And why were no other aircraft affected?
Which specific circumstances?

Originally Posted by GroundedSpanner

OK - Fair Challenges - good post, I'll have a go at answering and simultaneously expanding my own thoughts. In fact I'm not having a go at you, I'm more working my theory....

Experience. Without wishing to dox myself, I've worked in engineering at a major airline from apprentice through (in no particular order) Line Maintenance, Heavy and Light Maintenance, to technical support and maintenance control on both Boeing and Airbus products, with various qualifications and authorisations along the way. [Hmm - Scrap this sentence?]On the day 9/11 occurred, I should have been making modifications inside a fuel tank instead of staring at the TV with mouth on the floor.
However, I would describe my experience as broad, yet shallow in respect to this incident. Some of my fleet I know every rivet. Some of my fleet I've only ever seen from a distance. I don't touch airplanes for a living any more. B787 though - is not my area of specialty. I'll dig in, but am not the expert. I am not a systems design engineer, so precise numbers and flow rates, are not what I do. But what the systems do, how they operate, what they look like, smell and taste like... yeah, I'm not a muggle. And I do have access to all the manuals and know how to use them. And - let me be clear, I am speculating. I was advancing a theory. It WILL be some flavour of wrong. The investigation will reveal all.

I Agree, Water in fuel is not a novel concept. Aircraft fuel tanks attract water - fact. How much? It varies. I've sumped tanks and got no water, I've seen drops of water beading about in the bottom of a gallon jug, I've seen gallons of water. I've been so covered in fuel I cant smell it or think straight and taken gallon after gallon not being able to tell if its fuel or water. I also agree that 57% humidity doesn't seem particularly high - its not south east Asian jungle levels - but I'm not an expert at humidity, 32Deg c at 57% humidity at 02:30 am is not going to be comfortable for me though. I looked at recent weather in DEL, and those values were at the higher end of the range.
Further, I believe the prevailing weather conditions on the ground are less important when it comes to the volume of water getting in. Fuel is cold, or gets damn cold during a 9 Hr flight. Fuel Temperature Management is an issue for our Drivers. So as the fuel is used at altitude, Air enters the tank through NACA Ducts in the outboard end of the wing. Its beneficial to maintain a slight positive pressure, amongst other things to reduce evaporation. (Added complication, there is also the Nitrogen Enrichment system due to TWA800 - but that's more about processing the air in the tank to change the properties and make it non-explosive). Then as the aircraft descends, more air enters as the air pressure increases. Its the humidity of that air in the descent that is going to determine the volume of water entering the tank and potentially the fuel. The water in the air condenses on the sides of the tank because of the cold post-flight fuel. It doesn't dissolve into the fuel, but sinks to the bottom. Ground temperature / humidity and time will likely affect how much water condenses out of that air while on the ground. There won't be a huge amount of air exchange on the ground. Likely if the AC landed at 2am, then from sunrise as the tank warmed up, there would actually be a flow out of the vents.

What Features and procedures are there to mitigate Water? I apologise if my post gave the impression that there are no mitigation processes. There are. Water is well understood in the industry.
Well for a start, Features / Design. The Aircraft has a water scavenge system. Water doesn't mix with fuel, it sinks to the bottom being about 20% denser than fuel, so at the very lowest point in the tank, the water scavenge system (Powered by the Aft Fuel Pump through a jet pump, a venturi like system) will suck up the 'fluid' at the very lowest point, where the water would collect and in Boeings words 'drip' that fluid into the path of the pump pickup inlet (but I'd describe it more as a 'squirt'). The idea being that a small amount of water injected into the fuel will be consumed by the engines harmlessly.
There is also agitation. The wing tank pumps are pretty much running constantly, from before engine startup to after engine shutdown. The pumps are quite violent to the fuel and supply more pressure then the engine could ever need. Any excess pressure is dumped right back into the tank, quite close to the pump, in a direction that would further stir up the fuel and help break up any water into suspended droplets.
This all works if there is a small amount of water in the fuel. The water scavenge pickup is right next to the pump inlet, but a bit lower. Little bits of water get managed. Looking at the pictures of the system, I'd say a couple of gallons of water would do no harm at all.
But if there was significantly more water in that tank. Guessing 10-30 + gallons, then the pump would be circulating water, or highly water rich fuel.

Then there's the suction pickup. Its in the same 'bay' as the aft fuel pump and located a little 'higher' than the pump inlet and water scavenge inlet. But also located between stringers that can separate out the settled water ( I wish I could share the pictures, but more than my job is worth ) I can imagine the suction pickup being in a pool of 'stagnant' water.

I also saw a post from Metcha about the scavenge system blocking with Algae - I don't know about that (B787 not my fleet). But possible that could aggravate things. There's also the reports of the Indian AAIB looking at the Titan Biocide incident. Its possible that might be related and could modify the theory.

Procedures - There's the (at my airline weekly I think) procedure to 'sump' the tanks. There are drain points in the tank. Valves that you can push in with a tool and fluid drains. As described earlier (and videos exist on YouTube), you drain about a gallon of fluid and examine it for water. Most often in temperate climates (my experience), there's a few 'beads' of water in the bottom of the jug, moving about like mercury. Except when there's more. Sometimes there's a clear line in the jug, half water, fuel above. And sometimes a gallon of water, that smells like fuel. You drain it until you are sure there's no water.

Could 'that much' water have condensed in the tank? Well - There's the question. I guess the basis of the theory is that on descent into DEL, the wing tanks picked up some very humid air, which settled water into the tanks through the night. Then, as the theory I posited must work, the wing pumps must have circulated and suspended that water into the fuel.
By design, the water from the CDG-DEL arrival should have been consumed in the DEL-AMD Sector. But desperately clinging to defending my theory (I appreciate this is a hole), lets assume that at DEL the pumps were running for a long time. Lets assume that the pumps allowed the water to be dispersed within the tank prior to being used through the engines. Then - in the DEL-AMD sector, the wing tanks could have picked up more water.

How much water would cause a sustained flameout? I never posited a sustained flameout. I posited a significant reduction in thrust. Listening back to the rooftop video, which at first we were all listening for evidence of RAT, there's also a rhythmic pop-pop-pop of engines struggling. I think the engines were running, albeit badly. Heavily water contaminated fuel will do that. It doesn't have to be 100% water. Just enough water to make the engine lose thrust. Your 2 gallons per second figure assumes the engine running at full flow. I'm not a figures man, I'll not challenge that, I do recall flowmeters at max thrust spin like crazy. But an engine struggling due to a high perrcentage of contamination, is that using 2 gal/sec? or just trying to? What happens if there is e.g. 20% water in the fuel?

There are also reported incidents of engine flameout / thrust reduction that have all happened at altitude. Incidents that have been recovered due to the altitude and time available. I Posited that the engines would have eventually regained full thrust once the contamination worked though. But 30 seconds of rough engine is very different at 40,000 feet than it is at 100 feet.

The theory also relies on a second part - the electrical failure. That the electrical failure causes the fuel supply to switch, a few seconds after the failure. We go, at the point of electrical failure from a pumped centre tank supply to a sucked wing tank supply. It takes time for that different fuel to reach the engine.

Ive written enough and am tired. Must stop now.

Originally Posted by Magplug

Given the iron-grip that the government appears to have over the media, one wonders how the truth will ever surface?

Originally Posted by Gino230

UN stated that it is up to the Country leading the investigation on wether to release the report at all- a frightening thought.

Originally Posted by za9ra22

With all due respect, do you have any idea how a large scale investigation of this kind actually works, because it would appear not so much.

Not only are there agencies and personnel from outside governmental influence directly involved in the investigation, and playing an active as well as observational role, which makes it almost impossible to hide or obscure critical pieces of information or data, but other than a frenzy of any-nonsense-goes in the name of hits, clicks and ad revenue, the media play no role whatsoever in any part of the investigation.

The team itself will operate largely within a bubble, and team members don't talk to media or politicians - however much the media or politicians still need to flap their jaws because to both classes, silence is anathema. Furthermore, everyone who does this kind of work is a professional, well aware that any unofficial commentary is capable of severely compromising the investigation and other members of the team. Just as pilots who fly these aircraft are professionals with a hard job deserving of respect, so are those who investigate when things go wrong.

Originally Posted by WillowRun 6-3

When I saw the article in The Air Current, on one hand I hoped for the sake of the reputation of the publisher that the unnamed sources were legitimately informed, but at the same time, would not anyone legitimately informed have been subject to rather strict confidentiality and nondisclosure obligations?

Originally Posted by WillowRun 6-3

The first accident involving this type, and the different design fundamentals of the type (heavier use of electrical systems), would make any investigation authority especially careful not to issue incorrect statements. Perhaps the AAIB in India could be credited with understanding the high regard in which Annex 13 is held, and wanting, ..... perhaps desperately wanting, not to screw this up, not only in general terms but especially given the context. And add in the seemingly mystifying answers to what happened to Flight 171. If Annex 13 had a sentient presence, I'm convinced (mere SLF and attorney as I am) that it would concur with a "be careful, be very careful" approach to anything outside the tight circle of confidentiality within which the investigation occurs.

Originally Posted by Finalveridict

It seems like people are jumping to conclusions about the pilots and letting Boeing off the hook without proper investigation. Instead of providing a professional, detailed transcript of the cockpit voice recorder (CVR), we’re just getting casual comments about what the pilot allegedly said. Critical information—like the timing of transmissions, the checklist items completed before takeoff, and other key details that should be on the CVR—are essential for understanding what happened in the cockpit, especially since the crash occurred so soon after takeoff. In my view, the preliminary report feels too convenient for certain parties involved.

Originally Posted by Saab Dastard

(Admin/Mod)Folks, it appears that the message isn't getting through.
There were two professional pilots on that flight deck.
It is not acceptable to effectively accuse both of a criminal act, because there is no evidence to identify which hand - if either - moved the fuel switches, or for what purpose or reason.
Unless and until any such evidence is published by the relevant authorities, kindly desist from doing so out of respect for your professional colleagues.

Originally Posted by Abbas Ibn Firnas

From the report, there is no indicated time stamp identifying the point when one pilot asked the other "why did you cut off"
This could explain the the assumption that it took ten seconds to reverse the switch positions.
Cut off could have been noticed at any point later than 08:08:42 but before 08:08:52.

Originally Posted by Gupeg

I am not trying to be disrespectful, just put forward a different point of view, and you may well be right...

Originally Posted by Shep69

I flew the 777. The 78 switches are of similar design. They must be positively lifted and then moved with a robust over center block preventing them from moving after being bumped by something or other. Nothing I can think of in the cockpit could hit them with enough force to break the over center lock. IIRC none of our fleet had the side guard. It takes a conscious act to move them. The stabilizer trim cutouts are completely different red guarded switches.

Originally Posted by jimtx

They don't have to be positively lifted if the detent rounded out due to wear or if the switch installed was one that the SAIB referenced with the locking feature disengaged. I can't discern a raised boss on the body of the left switch in Fig.13, page 10 of the AAIB report. I assume those switches have some internal over center locking mechanism also besides the spring on the lever that would not be needed if there was no detent. I do remember writing up a 767 switch a long time ago when the Captain noticed the detent was worn and he could shut down without lifting.

Originally Posted by Diff Tail Shim

The Indian AAIB are avoiding a German wings event I fear. Actually I was in a flight deck of a EJR today. Start / stop switches are so bloody obvious on the overhead as main switches. Guarded and easy to observe by all. Control switches that are not required as a normal action put away from hidden positions and visible to all. Embraer actually design systems logically. Speaking to a Captain today, he confirmed that if the the thrust levers of an EJR are beyond flight idle, engines cannot be shut down by then engine start/stop switches being turned off! You need to drag the thrust levers back to idle to shut them down. First thing I was taught as an airframe engineer converting to dual trade is that the fuel system of a airframe should not restrict an engine to receive fuel from a commanded input by the pilot. Throttle position should drive that logic. Not a lazy Boeing combined FADEC and SOV switch.

Originally Posted by Seamless


I wouldn't put too much significance in the "01 second" since this still is close enough for an unintentional cause.

No matter what: The design and position of the fuel cut off switches is potentially prone for mishaps.

Originally Posted by blimey

Is 'transitioned' a standard AAIB phrase rather than 'selected', and would that have any reference to the physical position of the switch being recorded or just inferred?

Originally Posted by LTC8K6

Remember that engine 1 had actually relit and began to recover and engine 2 had also relit.
To me it's amazing that those big engines were able to do that in the time allotted.

Originally Posted by LTC8K6

Why would a suicidal pilot even allow the attempt to restart within 10 seconds?

Originally Posted by LTC8K6

Why wouldn't he yell out the other pilot's name and ask "What are you doing?" for the CVR theater performance?