Posts about: "Fuel (All)" [Posts: 1005 Pages: 51]

SLF here, but I did read all 3 threads. To me, this doesn't seem likely. But it got me thinking, what about the fuel switches being partially cross-connected left to right and right to left? If each of the 8 channels (4 for each switch) has its own connector, it could be possible. From what I understood from earlier posts, from the 4 channels of each switch, there are 2 can shut down an engine. If that's the case, assuming some cross-connection, a single switch movement might be able to affect both engines.

But, even if this were possible, there are problems with this hypothesis too. The problem would most likely be discovered during engine startup, if the engines are started one by one, not at the same time, as they probably wouldn't start unless both switches are set to RUN. And not sure how this would fit the various delays recorded on the FDR. And you still need something/somebody to move at least one of the switches after rotation to trigger the issue. Both switches being moved by the pilots still seems much more likely to me than some technical issue.

"Software faults" do not usually come out of the blue, for no particular reason. Just because it's recorded by software it doesn't mean that it's not something hardware related that triggers it. In a previous reply, not sure if in this thread, it was mentioned that the message meant that there was implausible data coming from those STAB cutoff switches, if I remember correctly. Something like a channel showing both on and off at the same time, or the other way around, or some other inconsistency. That could have been an intermittent issue, that might indeed not be reproducible with a BITE test, and just be cleared. But if the STAB cutoff switches did indeed have a problem, or one was suspected due to recurring reports, is it really so unlikely that they might try to look for some hardware issues, such as a loose connector? For the Lion Air accident involving MCAS, after repeated issues during previous flights, they did exactly that: disconnected and reconnected some connectors to check for issues, among other things.

Because the 787 is constructed from carbon fibre the traditional common return is not available through the structure. Boeing had to add several hundred pounds of copper wire to act as the grounding points throughout the aircraft.
The Stab Trim (Posn) Xdcr fault reported on the previous sector is very common on this type. Trouble shooting does not involve touching those switches or digging around the wires under the panel.

Please illustrate your point with a schematic or block diagram from Boeing or some other other credible source. Perhaps first showing that the EEC is in the path between the fuel switch and the HPSOV.

It's never too late for any of us to learn something new about the fuel valve control architecture and sometimes facts may be hard to separate from the hamster droppings.

Software faults, or non correlated maintenance messages can be induced by other factors other than a hardware fault.
EG. GPS faults are common among aircraft that fly around Turkey and other troublesome areas of the world due to GPS 'spoofing' or jamming. The problem is known and a procedure to reset the fault and verify that there is no 'hard' fault hidden in the hardware is used every day.

As I posted earlier in this thread, the Stab Trim (Posn) XDCR status message can be deferred under the MEL with a maintenance procedure that does not involve touching those switches.

If you would copy and paste which part of the preliminary report has raised this question in your mind, it will help get you a satisfying response from the other posters here.
The report is linked in the first post of this thread, and is attached to post # 3 in .pdf format .

Simply calls for both fuel switches to be moved to CUTOFF then back to RUN.

The fuel control switches are clearly central to the investigation as the cause of the accident, and it is public knowledge that there was a SAIB relating.

Simplest answer is often the best - they included it to show they had considered it?

Imagine this forum if they hadn't included a nod to the SAIB - 90% of posts would be about the SAIB. can't really win on this one in the court of public opinion.

Included or not, they made no recommendations for even proactive reminding of the SAIB to operators. This is more telling for me.

It also is both possible without imagining things, and consistent with - shall we call it "best practices" under Annex 13 - for the person or persons who wrote and approved the preliminary report to have taken into consideration the attention their report would receive from many audiences, not only aviation professionals.

The prevalence of the 787 type. The quite recent travails of Boeing and the pace of its recovery (and some doubters that it can or will recover). The orders of magnitude increase in information, as well as misinformation or even disinformation, about this accident compared to .... well, compared to the UPS accident in Birmingham in 2013 (Flight 1354), cited as it was the first "current" accident occuring as of my stumbling across this forum and its threads. Sure, not a dramatic passenger aircraft accident but still valid for comparing the information environment then, and now.

The persons responsible for this report, I think, did not act improperly if they included information not strictly necessary for the purpose of keeping aviation cognescenti updated about what is known with some (imprecisely defined) level of certainty and clarity. Such other information items could be intended to make some effort at mitigating ("minimizing" would be hoping for too much) the volumes of noise emanating from all over.

Then there's the point about the report source knowing who did what, and when, but not providing specifics. Perhaps forensic analysis of the voice recording is ongoing, perhaps an analysis was completed but with reason to examine more closely. Regardless, I do not find it an affront either to solid, long-established principles of the Chicago Convention and Annex 13, or to the general ideas about advancing aviation safety, for the report sources to not treat the 30-day rule for preliminary reports as some "complete download demand function." Given what is reported about the fuel cutoff switches moving and the summarized cockpit statements, either way the final facts resolve will be tremendously impactful for the airline, the CAA of India, and the country (including but not only in its role as a major aviation Member State).

I wouldn't hold this view if it was a question of deception. I see it instead as a matter of reasonable discretion, about both ..."what to leave in, what to leave out" (with apologies to Bob Seeger, "Against the Wind", 1980).

Literally what the Preliminary Report says happened. Even the Pilots' exchange fits within this context.

In my opinion, not enough attention is being paid to why the Pilot Monitoring might have *had to* execute the memory items for dual-engine failure.

There would have been multiple similar failures in different locations. The data for the EAFR is completely separated from the wiring and circuitry for the HP fuel valves. - And that on both engines.

That is nonsense. There is no "fuel cut-off module". The fuel cut-off HP valves are operated directly by the cut-off switches through simple latching solenoids. No computer involved, not part of any communication network of the plane. The FADECs (which itself are totally separated from the rest of the aircraft) only get information on the status of the switches; e.g. to faciliate engine restart.

The switches may not have been returned to run by the pilot who put them to cutoff, and it was unrecoverable, so why fight them?

References to the SAIB and to inadvertent switch activation should perhaps be put to rest but the quote you use is not a good basis for doing so.

The SAIB describes a defect in the installation of the locking mechanism that, if present, could allow inadvertent activation.

The SAIB does not state that the switch will snap back into cutoff.

The SAIB inspection procedure would not be possible if the switch snapped back to cutoff -

"1) Inspect the locking feature of the fuel control switch to ensure its engagement. While the airplane is on the ground, check whether the fuel control switch can be moved between the two positions without lifting up the switch. If the switch can be moved without lifting it up, the locking feature has been disengaged and the switch should be replaced at the earliest opportunity."

The person you quoted has either seen a different switch defect or the authors of the SAIB didn't know what they were talking about.

There\x92s a shock value there. Recognizing what happened then doing something about it. As the engines lose thrust it does take some time to analyze what happened. None of this is expected nor trained to \x97 dual engine failure after breaking ground.

No pilot is expecting to see the FCSs in cut off right after rotation. And is busy flying.

So I can see it taking a bit to be recognized and acted upon. There\x92s also the disbelief factor for the person remedying the situation.

Generally don't think it's a good idea to reply to own posts, but in this case wanted to keep things in context. A few interesting items of note:

1. ADSB readouts - according to FlightRadar24, the last ADSB transmission was at 71ft AGL. Is that significant given the RAT is seen already deployed at 150ft AGL per the estimate above? At 71ft AGL, the wheels are about 40-50ft off the ground, assuming aircraft attitude is unchanged between there and this image. Is that 1 or 2 seconds after rotation? Does this imply electrical issues?
1a. The timings for ADSB transmissions outlined by MrShed are not in sync with the estimates above - people have talked about a time shift in this thread. I do believe ADSB timestamps are by the receiving station.
2. The preliminary report timings from the EAFR for E2 fuel cutoff switch RUN -> CUTOFF to the RAT supplying hydraulic power disagree with the lower end of the 4-7s estimate above, and are only consistent if this picture was taken 6-7 seconds after rotation, in my opinion, because of the time (4-5s) it would take to cut off the fuel to E2, spool down to where the VFSGs stop providing AC power, and RAT deployment.
3. The Preliminary Report mentions that the RAT deployed "immediately after" lift-off. Again, I have to wonder, why didn't they provide the RAT deployment timestamp, even relative to rotation? If this is in fact the case, does this imply electrical issues, in line with the last ADSB altitude reading?

FR24 article https://www.flightradar24.com/blog/f...rom-ahmedabad/

Hi appruser ! I have quoted Pip_Pip 's post above because the position provides a better means to link ADS-B data to the sequence of events, since it's coming directly from the aircraft. The time stamp comes from the volunteer-run receiver, which might experience clock drift. Based on the public CCTV video, we also have a rough triangulation for the rotation, which occurs next to the high-speed turnoff for the third taxiway.

Note that the good folks at FR24 did not apply temperature correction to the barometric altitude (they corrected for air pressure and runway elevation); pilots on pprune have done the corrections themselves and arrived at slightly different values, so take those altitude numbers with a grain of salt. Note also that the 787 sends altitude in 25 ft. increments, and I don't know how these are rounded (up, down, nearest).

We do not know how long the RAT has been deployed in this photo, we only know it can't have been deployed later. I have learned on this thread that the CUTOFF switch will also cause the VFSGs to disconnect, i.e. the B787 systems will electrically isolate the engine from the power buses before it has spooled down. With a dual failure, this would leave the main buses unpowered in short order, so if all of this is correct, the RAT would have clonked into place very soon after the second engine was cut off. This would not depend on the turbine speed.

I personally do not know what items are logged on the flight recorder, but I imagine RAT deployment was not among them. If so, the conditions for its deployment would be logged, but it requires an analytical step to conclude it did, and a preliminary report typically has no analysis at all. Hydraulic pressure to the flight controls is likely logged, so the RAT delivering hydraulic power would be a matter of record.

Where is the RadAlt antenna on a 787? Is it in the nose, or further back between the main gears?

Well..... having read through the discussion here and looked at the critical info in the prelim report, this former Boeing (now current Airbus) pilot is confident the elephant can safely hide in his dark little corner for a while yet.

Lots of stiff competition for "most implausible theory" going on but I think my favourite so far is "could've mistakenly moved fuel control switches to cutoff when going for gear up selection". Geezus. 🤦‍♂️ Plenty of others, including engineering related ones, around this level of plausibility too. The phrase recorded on the CVR by one of the pilots involving questioning why the fuel control switches were moved to cutoff needs to be taken very, very seriously.

The fan has distinct signatures of the blade and shaft rates that will correspond to the N1 frequency and the number of blades. Usually the strongest harmonic is somewhere in the range of the 5th harmonic. These are readily detectable during N1 changes, the time domain spectrogram will show the rate that the engine accelerates, and in this case, it may well show the deceleration rate as well. The compressor and all fans that will give signatures in the cockpit tend to be constant RPM, and will show steady lines related to the relevant harmonics of the related shaft frequency. In this case, all of that will be academic, the data appears to be covering the event clearly.

With the image of the aircraft from the SE corner of the airport, it is pretty clear that the aircraft was performing admirably in compliance with Part 25 Subpart B up until the time that the music stopped. The rotate rate in the earlier video from the NE camera is nominal, and the SE camera shows a height and position along the runway that would have been appropriate for the certified performance. The operation was nominal until it went pear shaped, and at that point, even ol' Chuck Yeager hisself would have had a bad day too.

There are still possible factors that would have resulted in the information that has been provided to date that do not involve elephants. It is unreasonable to withhold judgement when there are enough curiosities in the event to keep the investigators busy? The issue of switch locking problems necessitates an in depth understanding of what that may have resulted in. That 2 switches would have the same fault type at the same time is.... unlikely, but stuff happens. Losing a Concorde due to a titanium fillet on a reverser cowl coming adrift on a preceding aircraft is also, stuff happens. Power levers walking back on some types is also a stuff happens event, one that should not occur, it comes up about every second year, and has done for decades. A single point failure remains the likely cause of this disaster, and there are only really 2 that make any sense; a failure of the electrical circuits for the fuel switches, which there is only one remote possible cause, and a cognitive/overt act by the crew, which stands in contrast to the CVR discussion which is dissonant to an overt action by a flight crew member.

I am in agreement with you.
At first I also found the time to react to FCSs being set to cut-off and switching them back on to be surprising -10 seconds is an awfully long time to do something that would appear to be a natural reaction to seeing the switch conditions.
At that stage there had not been an indication of who was the PF and PM.
With the information that the co-pilot was PF, it made me rethink that assumption, based on the experience gradient in the cockpit.
My gut feeling is that if the roles were reversed and a much less experienced FO either accidentally or deliberately selected the FCSs off , an experienced Captain would almost instantly recognize the issue and switch them back on in a flash, perhaps with a heap of abuse and admonishment.
In this case however, it now looks like we have an FO, who maybe in his peripheral vision saw the Captain reach for the switches and so his first reaction was "why did you turn them off??!". The Captain's reply "I didn't" now has him totally befuddled and perhaps some reluctance to override something that he is sure the Captain did but doesn't make sense. I now could completely conceive why he took so long to get them back on - all too late unfortunately....

Replace 'failure' in your quoted text by 'cutoff' and it becomes correct.

does the ORDER in which the switches were operated give us any clues which seat operated them? I would suspect that most pilots always go left switch then right switch, or the right then left each and every time when switching off. We are creatures of habit.

I haven't seen it mentioned it yet that if the stabiliser cut out switches had been left in the wrong position from the previous maintenance, when would EICAS or some other system alert the pilots to this? Would the alert be in close proximity to when the fuel switches were moved?

As others have said I think what this episode has revealed is it's too easy to turn off the engines in flight, and that the fuel cut-off switches should only operate when the relevant throttle is at idle? or should have a 10 second pause when no WOW signal

and a definite yes to cockpit video, protected so only accident investigators can access it. I can guarantee the third MCAS event wouldn't have happened if the 2 Lion Air MCAS events had been caught on video. It still shocks me after the first Lion Air near miss where the jump seater saved the day that the plane was released to service "nothing found". And as/when found cockpit video would solve the mystery of MH370.