Posts by user "BrogulT" [Posts: 24 Total up-votes: 67 Pages: 2]

Without getting into how an MEL actually works, here's an excerpt from an actual 787 MEL.



AGCU = APU Generator Control Unit, VFSG = Variable Frequency Starter Generator. IDK what exactly the AGCU does nor why the left one is important.

I don't see a problem with questions and people of any level of qualification can provide factual information. Questions can be answered and misstatements can be corrected. That said, better quality input is always welcome, but at this stage we're not likely to get much professional or official input. I hope the Indian authorities are transparent here and I think it is likely we'll have plenty of data.

IMO the problem is the relentless comments by people that apparently think they will win something by cracking the case or "calling it first" or those that can look at some AI rendering of a blurry picture and conclude they know the flap settings. Or concluding that a likely cause for this crash was that both engine master switches were turned off.
Of course dual fuel cutoff is a remote but possible answer, but not one worth speculating about at this point let alone concluding that's what happened.

https://www.flightradar24.com/blog/f...rom-ahmedabad/

Basic human nature or learned nature due to prior experience with prop twins where feathering promptly is critical? In case, is it in the SOP anywhere (perhaps a memory item, no time for checklists) that upon noticing inadequate takeoff climb performance you first need to urgently secure one of the engines (quick--which one!) before even reaching acceleration height? If not, are you suggesting that "human nature" will inevitably compel a properly trained crew to do so anyway? That seems pretty inane to me--there's no performance gain by shutting down a malfunctioning jet engine (which may still be producing residual thrust or may come back to life or ????) and they only had a few seconds to make that determination and execute the shutdown.

Also, I'm not sure exactly what you mean by "just off the runway after V1". I think V1 was probably some ways back.

Not a 787 pilot, but given the fairly high weight, calm winds and the 37C temperature, 184kn is not excessivly high for rotation. The data points are ground speed and a small decrease during initial climb doesn't seem surprising. It isn't "decreasing rapidly", it just drops a few knots. Simple geometry plus some small variance in airspeed and wind would account for that much variance and FR24 calculated speeds are not perfect in any case. I think it is more interesting that the data stops shortly thereafter. If the speed continued to decrease that would be an important clue, but we don't have that information right now. The surveillance video seems to me to show the plane at least exceeding a full wingspan in height, that means over 200 feet.

This is contrary to what is published here and elsewhere.

https://kb.skyhightex.com/knowledge-...7-fuel-system/

Can you state the source of your information? I have no way of independently verifying what I've provided. According to that, however, the two center tank pumps are higher pressure than the L/R tank pumps and will override them if both are activated. So the center tank fuel is used first, then the L/R tank pumps. If no pumps are operating, the engines can suction fuel from their respective L or R tanks provided there's enough atmospheric pressure. The end result is still that an empty center tank cannot cause an engine shutdown absent some other malfunction.

Good job piecing the two together. Flight time ~31s, climb seems to have fizzled out very soon after liftoff. IDK how anyone can listen to the audio on that first video and not conclude that the RAT is out and the engines are quiet. Unless the audio has been altered...

If you read the MMEL for the 787, like most passenger jets there's a LOT of stuff that can be inop and you can still dispatch. APU, one of two center hydraulic pumps, etc. Not suprising to those if you in the industry but perhaps mildly disturbing to the rest of us. I'm wondering how much other stuff could be not working without being noticed. Specifically I'm wondering about the suction pumping of fuel on the engines. Since the normal mode is to run all of the fuel pumps, the suction pump mode is always overridden by boost pressure from the electrics. Might it be possible for wear, improper maintenence or some other issue to cause this standby suction feature to not actually work? Is it routinely tested and if so, how often? The idea here is that if the engines were not capable of sucking up fuel on their own, the airplane would be operated indefinitely without anyone knowing until one day there is a catastrophic electrical malfunction at an inopportune time. In this case, that might correspond with the cessation of the ADS-B data.

I'm asking this as a question, not claming to have "cracked the case". I'm not an aviation fuel system expert. Can anyone who is or has direct knowledge comment? The reason I thought of it is that I've seen very similar issues with diesel engine systems where the mechanical injection pump can typically suck fuel but is normally fed with pressure. An internal (or external) leak can cause it to not be able to suction fuel properly but as long as the other pumps keep it pressurized it can work forever.

FR24 has stated that they processed additional frames and have published this separately. There are links to this earlier in the thread. What you see is the first data point is immediately after liftoff and then they are regular for a bit and then they stop. Apparently at least half of the runway has poor coverage and that is what led to the early conjectures that they had done an intersection takeoff. If you look at tracks from other flights from this airport, you'll see the spotty coverage on the first half of 23, but departing flights seem to have good data. YMMV, but that's what I saw when I looked at a few other flights.

Thank you for your qualified input! I had asked a question about the ability of the engines to suction fuel if the fuel pumps were inop. Specifically, I wanted to know whether that is ever tested and if so how often and by who. IOW, if due to wear, a maintenance mistake or whatever, if the engines were in fact NOT able to suction fuel, since the SOP is to run all of the pumps would that problem ever be noticed in normal operations? If not, then if both engines had that problem (imagine a faulty maintenance procedure that somehow caused this to happen to a lot of engines) then a sudden, complete collapse of the electrical system would cause the pumps to stop--and thus the engines. If any of that is even a possiblity then all of the other AI 787s should be checked.

I keep reading this theory and I'm baffled. You think the PF is going to attempt a dual engine shutoff and relight during the initial climb based on a hunch that the engines have quit, all without even a sideways glance to see what N1 is or a short word with the PM?

Is the ability of an engine to run using only suction feed ever actually checked or tested during operations or maintenance procedures?

In that case, I would think that it is not beyond the realm of remote possibility that for whatever reason there might be at least some of these in the field that will not actually function in the suction mode. And if we are talking about simultaneous dual-flameouts then we're already in the "realm of remote possibility", so they should be looking at these unlikely causes. If they're never tested, it's simply an unknown. Discussions so far just assume that this feature works. From what you say it would not be simple to test all of the in-service engines since the test itself is destructive. Perhaps there is some way to test without grinding up the pumps.

OK I can accept that two bad pumps are unlikely but what I originally wanted to know was when the suction-feed system--as a whole--is ever tested. Your answer as I understand it is effectively "never". So then I'd ask what other parts of the system are there--check valves, tubes, fittings etc--that have to work properly in order to get fuel to the engines without electric pumps? The engines are lower than the tanks so it really is suction-augmented gravity feed, but are there any points where a leak could air-lock the system? Is the fuel feed to the pumps via a standpipe going through the bottom of the tank or via a loop that enters from the top of the tank? There have been cases before where mechanics have systemically misassembled things.

I'm afraid that this reconstituted thread is more polluted worse than the original as mods try to hold back this flood of sewage. While there are multiple examples of air disasters caused solely by astonishingly egregious malfeasance by pilots, I see absolutely no point in unsupported speculation about such things. I can't ever say "no professional aircrew would ever do that" but spouting off random theories with no evidence and no practical experience or knowledge of the actual operations involved is really annoying and pointless. If you are a GA pilot, SLF with an engineering degree or a sim enthusiast then maybe, just maybe, you can manage to ask an intelligent question--preferrably one that hasn't already been asked and answered five times already. But please keep your inane hypotheses and conclusions to yourself for now. There's no prize for guessing correctly!

Perhaps we could reincarnate Alex Trebek to moderate the forum--the first rule is that unless you have significant expertise or are providing uncontroversial factual information (posting and FCOM or MMEL for example), all posts should be in the form of a question.

I certainly am not advocating excluding crew actions from consideration but I am saying that uninformed rank speculation on that particular topic has much more potential to be harmful to actual people. PPRUNE is widely read by news outlets and Youtube pontificators. Give them a "credible" reason and they'll be digging into the personal lives of the crew in ways that none of us would like. If you want to ask "what would happen if the captain just switched off both engines at rotation?" then I suppose the answer might be that the result would be pretty much exactly what happened here. But I think it is a bad idea to go there so soon and without evidence, especially since we're likely to have more evidence soon.

That's simply incorrect. In both cases the crew had realized the problem and manually advanced the throttle levers before impact--just not soon enough.

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

I was thinking that the flare at the end before they hit the ground was a good indication that up to that point there was not an excessively high AOA. Am I wrong or am I misunderstanding your point?

Wikipedia (I didn't check their cited source) shows 242 total on board--230 passengers, 10 FAs and 2 pilots. If correct, that at least means there wasn't a relief pilot.