Good grief - this has all been covered - repeatedly - in the Air India accident threads. I think some people here have a reading comprehension problem... :ugh:

I'll repeat - again: The Fuel Condition Switches are hard wired (with some interposing relays) from the switch to the spar valve and the fuel control High Pressure Fuel Shutoff Valve. PERIOD!!! It doesn't go through the FADEC, it doesn't go through any aircraft computers. IT'S HARD WIRED!!! Moving the fuel switch to CUTOFF provides 28 Vdc to the close coils of the spar valve and the HPSOV solenoid. The FADEC also gets the fuel condition switch position, but only uses it during the engine start sequence - once the engine is running, it doesn't use that signal for anything other than to set maintenance faults if there is some sort of disagree.

Once the engine is running, the only time the FADEC will attempt to shutdown the engine is if an N2 (N3) overspeed is detected, or through TCMA (using the same circuit as the overspeed protection).

35 °C or °F? The difference can be critical, depending where you are in the world. Ask that craft crash landing on Mars, part developed by metric speaking engineers, and others using imperial! Passing a parched Aussie a warm beer can invite death, whereas a warm pint for a Brit...

Has Boeing incorporated your idea in their latest designs? Time to approach Airbus too. For some, mere acknowledgement of a brilliant mind is worth more than financial reward. The converse is true - you need to put bread on the table. A 35 degree beer might be the solution. Cheers!

I can just see the latest raft of expert YouBoob videos and the gutter press headlines: Airline industry experts examining if AI171 was running metric software, and pilots wre served warm beer prior to takeoff.

35° F. Guinness 55° > hoping Boeing has lost my prototype, they wouldn't use it any way, no room to hide mysterious kit.

Cheers...!!

I was under the impression that cycling to CUTOFF then RUN would reboot the EEC/FADEC?

I've been looking at EAFR data from previous 787 incidents. As soon as the switch goes to CUTOFF, data from the EEC is flagged "invalid" for about 1 second, then becomes valid again. That seems consistent with what tdracer has mentioned (EEC reset takes about 1 second). 6 seconds after CUTOFF, the EEC "Channel In Control" switches.

The main electrical generators go offline almost immediately, regardless of turbine speed. The alternator that powers the FADEC keeps working. Compare:
Regarding the quick relight, I found this post instructive.

Thank you TDRACER for answering my question from post 176.
All the speculation about how the switches worked made no sense to me.

It would only take one pole failing (on EACH switch) to command the LPSOVs (and HPSOVs?) shut, or the associated relays failing. Still an extremely unlikely double failure, especially 1s apart.

This would also be, IMHO, blatantly obvious on the DFDR because you would see a fuel valves indicating closed and the engines running down, but the RDCs directly looking at two other poles of each switch would show the engines still being commanded to run. We haven't heard of this. It would be a smoking gun that would justify immediate grounding.

Not sure I understand (most likely not) - are you saying this is an intended dual-purpose of the switch: fuel shutoff (as primary use), but also reboot. Presumably, the latter is not actually used that much ... or is it?

Run-cutoff-run seems to be something of a last-ditch effort in all the troubleshooting guides.

Happened in US1549 where it almost certainly couldn't have helped as neither engine flamed out. Same as people were suggesting was intentional here.

I think there are suggestions that cutting and reintroducing fuel might clear some types of persistent compressor stall, but modern FADECs can probably detect that and do it themselves if necessary.

td
 

"Once the engine is running, the only time the FADEC will attempt to shutdown the engine is if an N2 (N3) overspeed is detected, or through TCMA (using the same circuit as the overspeed protection)."

Does FADEC Rebooting count...? Is the FADEC actioned cutoff logged in DFDR?⁸

So.....
Very suspicious... FO "Did you Cutoff?" CAPTAIN "NO, I did not"..... Neither one did, nonetheless there was CUTOFF
FADEC THEN .

Who better to reboot the FADEC than the Captain, who has thousands of hours in the Dream, and with respect, knows it better than anyone here??

CUTOFF was recorded at EAFR. Giving Boeing the excuse to claim the pilot(s) started the loss of thrust.

Knowing FADEC, WHEN HEALTHY, IS FASTER AT RELIGHTING OR RESTARTING THAN A PILOT, DID CAPTAIN CHOOSE TO WAIT FOR FADEC TO SORT THE GEs ???

I Dunno. But we know they did not restart in time.

Bugly

The FADEC cannot action the fuel cutoff switches - those are mechanical switches with no solenoid or motor. Their position is recorded in the EAFR as recorded by I think one of the remote data concentrators (RDCs).

A FADEC initiated shutdown will show up in the EAFR data as TCMA or N2 Overspeed - someone posted the exact names for the fields earlier.

I am not certain whether a FADEC reset alone necessarily flames out the engine. This would presumably have to be initiated by a FADEC self-test failure or an electrical fault, to get a reset without cutting fuel.

I'm not saying I do, but we've seen plenty of evidence that line pilots don't fully understand their aircraft.

The FADEC is the only thing that can restart the engines. All the pilot can do is give or refuse permission. 'Full Authority' digital engine controller.

HAMSTERWHEEL ALARM

Not really Hamster territory. I find it an interesting, informative discussion. Also, I suspect that tdracer knows a lot more than many pilots.

In case this hasn’t been asked

How many more seconds would have been needed for the engine that was closest to relighting before it could produce enough thrust to save the aircraft ?

Simon Hradecky writes:Is this true? He doesn't cite any sources.

I don't know anything about the claim of engine relight needing an extended pause in the "CUTOFF" state, but IIRC, it has been stated here or in the main 787 crash thread that if the FCS's are switched to cutoff with the engines running, the engine starter-generators are preemptively disconnected from their electrical buses, without waiting for the engines to roll back below normal idle. This would invalidate a key part of Hradecky's analysis.

With respect...one thing I've learned since I've been on PPrune is that there's always someone who knows more than you do.
There are pilots and engineers within these boards that have forgotten more about the 787 than the AI captain ever knew.
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A further comment: I also tried posting to AVHerald a comment on Simon's article, similar to the one I made here (and at about the same time) regarding the supposed preemptive shutdown of electrical output from the engines with operation of the FCS to CUTOFF. That post disappeared into the Internet ether, in what I assumed was some AVHerald glitch, and having spent some minutes composing it, I just gave up and did not try again. The AVHerald reply mechanism requests an email address that is supposedly kept private. But as I don't have confidence in such assurances, I offered a backup email I use for such occasions, but don't regularly monitor.

Today I was surprised to find Simon had made, some days ago, a long and detailed private response to my comment via that email. He also stated that my referencing PPRUNE in that comment was cause for my comment to be suppressed: "Referencing other sites is not permitted, whether by URL, name, abbreviation of [sic] whatever. Hence your message was suppressed." (Seems a bit strange!)

I'm just recovering from 24-odd straight hours of SLF flying, so am not compos mentis enough to study the considerable details in both the original Hradecky post and his personal reply, but if I have time in the next few days, I will do so.

But meantime I would simply suggest posting your question to AVHerald (but for heavens sake, don't mention "PPRUNE") and I suspect he will respond.