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Lonewolf_50
2025-06-30T13:08:00 permalink Post: 11913613 |
We know that the right-hand GEnx-1B was removed for overhaul and re-installed in March 2025 so it was at “zero time” and zero cycles, meaning a performance asymmetry that the FADEC would have to manage every time maximum thrust is selected. If the old engine was still on the pre-2021 EEC build while the fresh engine carried the post-Service Bulletin software/hardware, a dual “commanded rollback” is plausible.
A latent fault on one channel with the mid-life core can prompt the other engine to match thrust to maintain symmetry, leading to dual rollback. ![]()
Originally Posted by
silverelise
He also confirmed that all the data from the recorders has been downloaded and is being processed by the Indian AAIB,
no boxes have been sent abroad.
The 30 day deadline for the preliminary report is July 12th.
Originally Posted by
the linked article
Investigators still haven’t ruled out the possibility of sabotage being behind the Air India crash in
Ahmedabad
earlier this month that
killed 274 people
, according to India’s aviation minister. The Aircraft Accident Investigation Bureau (AAIB) has confirmed that the aircraft’s flight recorders – known as black boxes – will not be sent outside the country for assessment and will be analysed by the agency, said Murlidhar Mohol, the minister of state for civil aviation.l
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skwdenyer
2025-06-30T14:04:00 permalink Post: 11913652 |
Posters may like to read this old (2016) pprune thread on 787 engine failure procedures:
787 engine failure procedure
Some interesting comments about how a combination of ATM and derate can lead to some pretty surprisingly poor outcomes, coupled with Boeing advice not to advance thrust levers or engage TOGA. (edited for poor spelling) Last edited by skwdenyer; 30th Jun 2025 at 14:40 . |
adfad
2025-06-30T15:49:00 permalink Post: 11913716 |
India's Minister of State for Civil Aviation appears to be confirming in this interview that the cause of the accident was a dual engine failure. Which is, I think, the first vaguely official confirmation of what happened that has been released? He also confirmed that all the data from the recorders has been downloaded and is being processed by the Indian AAIB, no boxes have been sent abroad.
The 30 day deadline for the preliminary report is July 12th.
The minister called the crash a \x93rare case\x94 and, referring to claims by veteran pilots and experts that a dual-engine failure may have led to the crash, said: \x93It has never happened that both engines have shut down together.\x94 \x93Once the report comes, we will be able to ascertain if it was an engine problem or fuel supply issue or why both engines had stopped functioning.
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Capn Bloggs
2025-06-30T16:26:00 permalink Post: 11913745 |
Richard Godfrey has completely ignored that fact that the speed was reducing all the way down the descent. He has hypothesised a steady descent angle at around 3.5:1 and therefore concluded that one engine had stopped and the other was on ~10,000lb of thrust because, at the initial speed they needed that thrust to counter the drag. But the AOA clearly increases markedly as the aircraft approaches the ground, which means that the speed was reducing significantly.
As for statements such as:
One Engine Inoperative (OEI) just before take-off(Assumption).
​​​​​​​The Take-Off Speed at rotation is estimated at 160 KIAS (167 KTAS, 170 GS), which is higher than normal and expected in an assumed OEI take-off.
​​​​​​​The rotation point requires a runway ground roll of 2,540 m, which is longer than normal due to an assumed OEI take-off.
​​​​​​​The climb gradient is estimated at 5.09%, which is slightly above the normal range of 3% to 4%at TOGA for a Boeing 787-8, but within limits
​​​​​​​True airspeed was under-indicated due to low density, in other words the aircraft was moving faster through the air than the airspeed indicator showed, because there were fewer air molecules hitting the pitot tube in the hot, thin air
​​​​​​​The aircraft peaked early, then levelled off and started descending while passing over obstacles. It barely cleared Obstacle B by ~50 feet, which is tight, but sufficient. This explains the visibly profile in video and supports the notion of degraded climb due to hot/high conditions, heavyweight, and limited thrust margin
In a nutshell, he's saying they had an engine failure before rotation, then got all the way up to 300-odd feet (following what looked to me like an initially standard low-angle/flat 787 takeoff, then ran out of puff and crashed with the other engine running at 15-18% Thrust. Pure speculation aka WAG. 11 users liked this post. |
87guy
2025-06-30T16:32:00 permalink Post: 11913751 |
Richard Godfrey has completely ignored that fact that the speed was reducing all the way down the descent. He has hypothesised a steady descent angle at around 3.5:1 and therefore concluded that one engine had stopped and the other was on ~10,000lb of thrust because, at the initial speed they needed that thrust to counter the drag. But the AOA clearly increases markedly as the aircraft approaches the ground, which means that the speed was reducing significantly.
As for statements such as: They make me take that whole spiel with a grain of salt. In a nutshell, he's saying they had an engine failure before rotation, then got all the way up to 300-odd feet (following what looked to me like an initially standard low-angle/flat 787 takeoff, then ran out of puff and crashed with the other engine running at 15-18% Thrust. Pure speculation aka WAG. 2 users liked this post. |
Sailvi767
2025-06-30T18:57:00 permalink Post: 11913849 |
I found descriptions on the systems of the 787 were easily discovered online, and while I have no hands-on experience of aircraft related matters, I do have experience in wider electrical theory and maintenance.
THRUST Asymmetry PROTECTION. "For an engine-out condition, Thrust Asymmetry Protection (TAP) reduces thrust on the operating engine to ensure there is sufficient rudder for directional control. TAP reduces thrust when the airspeed decreases below approximately V2 on a takeoff or below approximately VREF on a go-around. Once speed is increased above V2/VREF, TAP increases thrust." From what we know so far, it does seem the engines were not producing sufficient thrust, during a period when it would also be crucial to maintain electrical output for the electro-hydraulic systems and critical electrical loads. Reduced electrical output could explain the failure of the gear to complete retraction, maybe caused by a generator failing at the worst possible moment. If there was an EFATO, the ability of the remaining generators to provide sufficient power might become questionable, as is highlighted with the load shedding system. Other features which are unique to the 787 could be contributing factors in explaining the accident. It is known the 787 will generally employ an extended take-off roll, and a relatively higher V1 and Vr, and also climb out less steeply than other aircraft. Using more of the runway would reduce the margin for aborted take offs. With the evident lack of thrust early in the climb out, and failure to retract the gear, if V2 had not been maintained, the TAP system would have reduced thrust even further. Manually increasing thrust will be inhibited. 2 users liked this post. |
GroundedSpanner
2025-06-30T21:18:00 permalink Post: 11913900 |
It would go against every aspect of training for a professional crew to deploy the rat below 400 feet. Further if you put 100 crewmembers in a simulator on takeoff and said deploy the rat manually I would bet not a single crew member could find the rat deploy switch and activate it in under 5 seconds and maybe 2 or 3 in 10 seconds.
It can auto-deploy in a significant electrical failure. The theory I'm working is that, given the configuration of the aircraft, if there is a significant electrical failure (sufficient for the RAT to auto-deploy). The aircraft fuel pumps are lost. Approx. 7ish seconds after those fuel pumps are lost (if the engines are at TOGA), the fuel being received by the engines is arriving from a different source, a potentially contaminated source. I believe that the engine failure is a secondary result of the power loss (with specific circumstances). But this all hinges on whether the engines were trying to run, or commanded off. Hence the request for interpretation of the sound. 1 user liked this post. |
za9ra22
2025-06-30T22:04:00 permalink Post: 11913913 |
that, given the configuration of the aircraft
if there is a significant electrical failure (sufficient for the RAT to auto-deploy)
The aircraft fuel pumps are lost
the fuel being received by the engines is arriving from a different source
a potentially contaminated source
I believe that the engine failure is a secondary result of the power loss (with specific circumstances)
It isn't that your suppositions are necessarily bad ones, but that they seem a bit of a stretch. Of course I'm no expert, hence asking. Last edited by za9ra22; 30th Jun 2025 at 22:19 . 2 users liked this post. |
GroundedSpanner
2025-06-30T22:21:00 permalink Post: 11913922 |
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. Last edited by Senior Pilot; 30th Jun 2025 at 23:01 . Reason: Quote from a week ago; this is not a Hamsterwheel thread, thanks! |
fdr
2025-06-30T23:39:00 permalink Post: 11913950 |
We know that the right-hand GEnx-1B was removed for overhaul and re-installed in March 2025 so it was at \x93zero time\x94 and zero cycles, meaning a performance asymmetry that the FADEC would have to manage every time maximum thrust is selected. If the old engine was still on the pre-2021 EEC build while the fresh engine carried the post-Service Bulletin software/hardware, a dual \x93commanded rollback\x94 is plausible. A latent fault on one channel with the mid-life core can prompt the other engine to match thrust to maintain symmetry, leading to dual rollback.
3 users liked this post. |
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