Posts about: "Thread Moderation" [Posts: 120 Pages: 6]

100%. As pointed out many times, this accident just doesn\x92t fit with either performance errors, flap/gear mis-selection or inappropriate AP/AT modes. The flightpath was as expected until shortly after liftoff, then we see/hear RAT deployment and an unpowered descent into the ground. There are still plenty of possible reasons as to why this occurred but to date we can\x92t really narrow it down any more.

Mods, feel free to remove this if you think it's not contributing.

Folks, the exchange here about the cutoff switches ("fuel control switches") is exactly the kind of discussion that contributes meaningfully to our collective understanding of one possible causal or contributing factor in the accident. Smart, well-informed people politely considering and evaluating the suggestions of others. No snark or sniping. Love it.

I think the mods are right to squelch vapor-lock theories because AFAIK there's no support for the notion that it would happen under these circumstances. I can provide a brief explanation but I don't know the operating parameters of a 787 fuel system so I can't speak authoritatively on that. I can speak authoritatively on modern automotive fuel systems where vapor lock on a running system is just not a thing, even though gasoline has much higher vapor pressures and cars can be operated in temperatures much higher than 43C with fuel temperatures to match.

This explanation comes with a money-back guarantee and if I'm wrong I'll send out refunds.

First, vapor lock is simply where a pump or other device becomes inoperative because it is designed to pump liquids but is presented with a gas (vapor) at it's inlet and thus cannot develop pressure and pump the fuel. Think of a very old car with a mechanical fuel pump on the engine block that draws fuel through a long tube from the fuel tank. If you shut the car off on a hot day, the residual heat may boil off the fuel in the lines and carburetor so that when you try to restart, there's no fuel anywhere and your pump has lost it's prime. It is key to note that even with a very crude system like this and volatile gasoline as a fuel, vapor lock usually only affects starting and not running engines. There are exceptions, of course.

The three key factors are the absolute pressure at a particular point in the fuel system, the vapor pressure of the fuel at whatever temperature it is at and system design. System design has all but eliminated vapor lock as a serious issue in the gasoline automotive world. At near sea level, the outside pressure is about 1 bar (15psi) and at 50C typical jet fuel will have a vapor pressure of perhaps 0.02 bar. So the only way to cause it to vaporize jet fuel, even at 50C+, would be to subject it to a very, very strong suction. AFAIK there are no vulnerable points where you'd have suction during normal operation because the fuel pumps are presumably (I don't actually know) immersed in fuel and the entire system has greater than 1 bar pressure all the way to the high pressure pumps. Even without the electric pumps, the inlet to the mechanical pump is below tank level. So absent some major fuel line restriction, there aren't any points where you'd have strong suction aka very low absolute pressure.

The discussions about fuel temperature also seem a big irrelevant to me--even at 60 or 70C the vapor pressure is still very low and I doubt you'd see significant vapors at all under 100C with any reasonable fuel system design and properly blended fuel . I'm assuming the fuel temperature limits are for other reasons, perhaps flash point or ignitabilty (TWA 800) or viscosity and lubricity concerns with the high pressure pump. Again, IDK, but vapor lock with Jet A seems very far fetched to me. I would note that improperly blended fuel could have a much higher vapor pressure and still work OK in most cases as long as positive pressure was maintained. So if the electrics and the pumps went offline and the fuel vapor pressure was way too high, I suppose there could be vapors formed in the suction line going to the mechanical pumps. But I don't have nearly enough knowledge to proclaim that as a possibility. I presume they've taken fuel samples at the source and tested them. Here's a paper on Jet A vapor pressure:

https://www.researchgate.net/publica...Kerosene_Jet_A

Fuel guy here. I've been "sitting on my hands" as requested by the mods but I will bite on that. Because dual engine failure is a "common mode fault" contamination is one of simplest explanations. Forget wax, think sediment, water or misfuelling. The only reason this has been discounted in favour of an electromechanical/software fault is that there is no yaw, i.e. both engines ran down at the same time at more or less the same rate, and would have to have been fed from the same tank (so the contaminated fuel reaches the engines at EXACTLY the same time on each side - is that even possible?). Its a stretch but I suppose it is possible, however the retention samples should have been tested by now. I would be interested in confirmation that they were taken and tested. I would also want to know if there is a "hot hydrant" system at AMD or if there are bowsers and if any maintenance had been done (think Cathay at Surabaya). But honestly, the fuel supply chain is usually rigorous...[edit: I have just seen a Reddit post pointing to a major construction project involving the fuelling facilities at Ahmedabad...will try to find out more...]

Obviously time for yet another reminder to read the threads and refrain from repeating questions and answers that have already been raised.

This is verging on the edge of becoming a Hamsterwheel and We Mods have far more to do on the Site than read back over pages of speculation and guesswork to weed out the gems that really contribute.

Yes PLEASE! I'm a Journalist and a (Private) Pilot and find it incredibly frustrating when people post quotes from "sources" without revealing the source of the quote with a link to the original article. No link? I ignore the post.

There is way too much misinformation floating around nowadays and I don't want to read it on this forum. PPRUNE has been a fantastic source of knowledge for me personally - especially leading up to my PPL exams in 2006.

Back then I could trust much of what I read on here. Thankfully the mods do a fantastic job and manage to weed out most of the nonsense but it takes time and I think it puts off many of the legit professional flyers from posting here.

What also winds me up is the amount of posters including YouTube links to dubious channels invariably presented by old blokes wearing epaulettes and claiming to be professional pilots. I wish these links could be banned. YouTube is not a source of news. It's a public website where anyone can post any old rubbish and pretend that it's real when it isn't. It worries me that so many people assume that "because it's on YouTube it must be correct"!

And FR24. It's a commercial website for aircraft spotters. It is not an accurate source of information for professional flyers. If I see a poster linking to it I ignore them as well.

It really is quite difficult now to "sort the wheat from the chaff" particularly on threads devoted to aircraft accidents. Thank you MODS for making it slightly more bearable!

This sounds convincing, but I have read the investigation report on Jetstar Airways serious incident (VHVKJ) with great attention, and if I understand it right, things may be a bit more subtle:

First, the problem involves the valves (notably but not exclusively FMV and FSV), not the combustion of the product:
Second, the doses apparently don't need to be that high to result in a problem. A x10 dose seems sufficient:
Third, the main cause of the incident seems to be associated with magnesium salts dissolving in water instead of fuel:
Fourth, and despite the report indicating that ( my bold ) "In this serious incident, it is highly probable that, when the Aircraft was descending for landing, there occurred oscillation in rpm of each engine causing both engines to temporarily fall below idle at separate times because Residue primarily composed of magnesium salts accumulated in spools impeded movement of spools that involved in fuel metering of both engines.", it should be noted that the reported "rpm oscillations" of left and right engines were close to each other in time:



These "rpm oscillations", leading to substantial loss of thrust, could as well have occurred simultaneously, and 81 seconds (for the RH engine) is an awfully long time. According to the report, Kathon FP1.5 is not used anymore for biocide treatment, but another contributor ( nachtmusak , who seems to be a petrol specialist) suggested that other products may have similar effects .

Therefore, regarding the case we are discussing at large (thanks again, mods!), I think we shouldn't overlook the hypothesis of fuel contamination by biocide, since it is a single point of failure (among a very limited number of SPoFs) from a system analysis point of view.

While suspecting that mods may consider this subject outside the realm of this thread - and I think it was raised previously - I have to say that to my mind, there would be significant questions over the integrity and reliability of data collected via third-party commercial businesses or agencies which may or may not have vested interests, and the vulnerability to any transmitted data to unauthorised and unknown outside access.

Just that last consideration, meaning the need to introduce information security 'experts' into the analysis of data might create far more problems than it solves.

On edit:
The reason why I think this is relevant to the Air India thread is that - as outlined in the discussion of FPGAs previously - aviation and avionics is becoming more and more sophisticated and specialised, and the need for rapid data analysis in an accident isn't just one of public impatience. Potential failure modes in increasingly complex systems make for an increasing need to pinpoint critical issues rapidly enough to mitigate them.

If the data is either encryted and/or signed with a suitably validated certificate, then any tampering becomes immediately obvious which itself makes the tampering pointless especially if it is sent via multiple routes.

SLF here. Mods - please delete summarily if this does not contribute to the discussion, I have no wish to waste anyones time. No 'AI' was used in the preparation of this post.

My understanding is that, as you say, the CAM has a preamp. That preamp can be powered by the RIPS that accompanies the forward EAFR.
In addition, I believe there is a single analogue connection from the CAM+preamp to the aft EAFR in addition to the analogue connection from the CAM+preamp to the forward EAFR. I believe, but am not sure,that the other flight-deck audio (headsets) is carried digitally over the fibre-optic network to the aft EAFR. The network may or may not be in operation in the event of an electrical failure: I simply don't know.

The publicly available information I can find is not stunningly clear about this.

AEROSAFETY WORLD, January 2008 - https://flightsafety.org/asw/jan08/a...47-48.pdf?dl=1

GE Aviation: Consolidate and increase recording power with the 3254F EAFR. - https://www.geaerospace.com/sites/de...rder-3254F.pdf

As for power, this NTSB document describes the power set-up for the EAFRs

https://data.ntsb.gov/Docket/Documen...ort-Master.PDF

So the forward EAFR is powered from the left 28V DC bus with the possibility of being powered by the RIPS, and the aft EAFR is powered from the right 28 V DC bus.

What I have been unable to determine is whether the right and/or left 28 V DC buses are powered from the main battery in case of failure of the AC power supply. To my untrained eye, it looks like the Captain's flight displays are powered from the main battery in extremis (28 V DC - C1), but that there are various circuit breakers, that could be automated, that may or may not allow or prevent other loads (such as the F/O's flight displays (28 V DC - C2), or the aft EAFR, being supplied by the main battery, (See link to diagram). There could well be very drastic automated load shedding.

https://kb.skyhightex.com/wp-content...l-1024x640.png

If the right 28 V DC bus was unpowered for any period, it follows that the aft EAFR was not recording for that period. This would make the forward EAFR important in case of a power failure that prevented the right 28 V DC bus from providing power.

All the information that is unclear to me will be transparently clear to the crash investigators. But it seems to me that the aft EAFR will not hold data for any period that the right 28 V DC bus is not operating. Whether that applies to this incident is an open question.

I am starting to see the hamsterwheel references now.
Having two combined recorders is already more backup than what had previously been the norm, in addition theres the independently powered area mic going analog to the front recorder.

The common models I have checked the sheets for also provides a digital output (which is probably sent to the aft recorder via normal busses.

Having a seperate analog line going to the aft recorder would be several Kg of extra weight, and probably a substantial amount of loom design and paperwork for what is then a backup to an already redundant system.

Hence, imho why this signal only goes to the forward recorder. It is already a \xabbonus\xbb.

The power for microphone and preamp is in the >1watt range range, completely insignificant.

I am still interested in reliable information as to what is expected to be on the recorder of an aircraft which has lost the generators, what about the battery powered prinary instruments? Does some systems and the aft recorder come online with the RAT or would everything be down to the one cockpit mic? Surely not?

Two minor points regarding competence and who gets the task of data extraction from the data recorders: Firstly, that it's the AAIB (India) which will decide where and when to hand over the data recorders, and secondly, the supposed comment attributed to the Ministry of Civil Aviation in the press release dated June 19 ( https://www.pib.gov.in/PressReleaseP...x?PRID=2137718 ), that "t he decision regarding the location for decoding the flight recorders will be taken by the AAIB after due assessment of all technical, safety, and security considerations " would likely have been phrased rather differently if the lab in India were not considered capable of the work involved.

On edit:
And mods, apologies, this is getting rather more tangential to the incident than I intended!

Having given this thread plenty of time to settle, plus plenty of notice from various Mods, it has become a Hamsterwheel with no beneficial posts contributing to the thread for some time. That is including the dozens of Moderated posts you don't get to see, just in the past 24 hours!

Thread closed until the next official announcement.

Meanwhile, those of you now with time on their hands, please consider updating your Personal Profile to accurately show your professional aviation qualifications. That will both help us when Moderating and show the naysayers how to judge your posts

Thanks for doing this.
Someone else created an external page a few days ago that indexed and sorted all the topical posts in this thread and the original one under major headings.
I can no longer find it. Did that get deleted by mods for non compliance or is it still around somewhere?

That is here, in the Moderation thread: Moderation of Air India accident threads

It is here: https://paulross.github.io/pprune-th...171/index.html
I'll update that from time to time.
The project that does that is here: https://github.com/paulross/pprune-threads
If you have any suggestions raise an issue here: https://github.com/paulross/pprune-threads/issues or PM me.

The June 30, 2025 edition of Aviation Week & Space Technology (reviewed from an email with "Editors' Picks" sent to subscribers) includes an article dated June 27 by Sean Broderick, about the investigation of Air India 171. It relates some new facts or factual infomration (as well as coverage of many facts in the public domain for some time already).

One theme of the article is that the timing of release of information, in general about the investigation and specifically about data discovered in the recorder(s), appears inconsistent with other facts about the investigation. In support of this theme, the AW&ST article quotes a former NTSB investigator (with specific aircraft accident investigation experience).

The article also refers to the progress of work at the accident site (including an estimate of the number of workers involved) and the presence of aircraft accident investigation professionals from highly experienced authorities and entities (U.S. NTSB, U.K. AIB, Boieng, GE). It is pointed out - certainly with respect and diplomatic tone - that the aircraft accident investigation authority of India has relatively less experience in such matters. And that the presence of more experienced participants in the investigation (as accredited representatives, if I hopefully recall study of Annex 13 correctly) would suggest that guidance to the India authority has been available.

As the foregoing suggests the article asserts, in a thematic sense, that the timing of information release is not consistent with factual information about the investigation. (It also generally suggests that information typically is released by investigation authorities earlier within the initial 30-day time period provided for by Annex 13 .... but that generalization, while true in some cases, isn't backed up with anything specific of a factual nature.)

Mods, I hope this adds to the thread and if not please don't miss the bin when it gets tossed.

Nobody here could answer that, but since the authorities in India have said the recorders themselves are there and not going anywhere, I would guess that if any data has been downloaded and shared outside the country, it will be for specific analysis purposes - GE for example.

There's no credible reasons 'three former accident investigators' in the US would have any direct knowledge, and if any third party in the US has been provided access to data, it will have been on the basis that it is not shared. Even that I would doubt, since involved parties are far more likely to already be in India as part of the investigation.

On edit, and mindful of the Mods comments around the closing of the thread previously: I don't speak with any direct knowledge of accident investigations in India, only the UK - and even then with only one experience of civil aviation accident work. But I have been involved (in human factors as investigator and lead) in several UK incidents of scale, and have some familiarity with how these processes are constituted and work... there at least.

Yes there are. I'm not asking you to buy the whole story. Reason for electrical bang is not THE important bit.
THE important bit is - Electrical Bang + some seconds = fuel is from a different source.

Mods have removed my post text and replaced it. Annoying, as it was revised from a week ago. I don't have all the answers,


Somewhere upthread there was conversation about the new Fuel farm at AMD.
But they do use bowsers at at DEL...... and there is evidence of 'interference'.
A story about a very recently busted fuel Theft syndicate at DEL



EDIT - There's some good conversation going on about whether the Centre pumps are actually running at takeoff. If it can be proven that they are not running at takeoff, then the whole theory is based on a massive incorrect assumption and I will respectfully withdraw it.

Hello Posters,

Two of our members have drawn attention to the following article. As we approach the due date for the initial report, I'm sure the focus of the investigation will narrow, and discussion will be worthwhile. Than you very much to everyone for waiting patiently while this investigation progresses, 'thread's open for a while, 'same posting guidelines as always please:

Before you post a new theory or question, please search back or read back in the thread to see if that topic has been discussed/dismissed earlier. Once themes have been justified as not likely relevant (contaminated fuel, for example) let's not start a new discussion on that topic, unless an authoritative report brings it back to the forefront. A search/review you will do is a kindness to everyone, mods in particular! Thanks!

The referenced article:

https://www.reuters.com/world/india/...ry-2025-07-08/