Posts by user "Alty7x7" [Posts: 17 Total up-votes: 0 Pages: 1]

Alty7x7
June 12, 2025, 19:01:00 GMT
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Post: 11899608
Engine type

Line Number 26, GEnx-1B, delivered Jan 2014

Subjects: None

Alty7x7
June 13, 2025, 03:02:00 GMT
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Post: 11899948
Originally Posted by tdracer
OK, I promised some informed speculation when I got back, so here goes:
Disclaimer: never worked the 787, so my detailed knowledge is a bit lacking.

First off, this is perplexing - especially if the RAT was deployed. There is no 'simple' explanation that I can come up with.

GEnx-1B engines have been exceptionally reliable, and the GE carbon composite fan blades are very robust and resistant to bird strike damage (about 15 years after the GE90 entry into service, I remember a GE boast that no GE90 (carbon composite) fan blades had needed to be scrapped due to damage (birdstrike, FOD, etc. - now that was roughly another 15 years ago, so is probably no longer true, but it shows just how robust the carbon composite blades are - far better than the more conventional titanium fan blades).

Not saying it wasn't somehow birdstrike related, just that is very unlikely (then again, all the other explanations I can come up with are also very unlikely ).

Using improper temp when calculating TO performance - after some near misses, Boeing added logic that cross-compares multiple total temp probes - aircraft TAT (I think the 787 uses a single, dual element probe for aircraft TAT, but stand to be corrected) and the temp measured by the engine inlet probes - and puts up a message if they disagree by more than a few degree tolerance - so very, very unlikely.

N1 power setting is somewhat less prone to measurement and power setting errors than EPR (N1 is a much simpler measurement than Rolls EPR) - although even with EPR, problems on both engines at the same time is almost unheard of.

The Auto Thrust (autothrottle) function 'falls asleep' at 60 knots - and doesn't unlock until one of several things happens - 250 knots, a set altitude AGL is exceeded (I'm thinking 3,000 ft. but the memory is fuzzy), thrust levers are moved more than a couple of degrees, or the mode select is changed (memory says that last one is inhibited below 400 ft. AGL). So an Auto Thrust malfunction is also extremely unlikely. Further, a premature thrust lever retard would not explain a RAT deployment.

TO does seem to be very late in the takeoff role - even with a big derate, you still must accelerate fast enough to reach V1 with enough runway to stop - so there is still considerable margin if both engines are operating normally. That makes me wonder if they had the correct TO power setting - but I'm at a loss to explain how they could have fouled that up with all the protections that the 787 puts on that.

If one engine did fail after V1, it's conceivable that they shut down the wrong engine - but since this happened literally seconds after takeoff, it begs the question why they would be in a big hurry to shut down the engine. Short of an engine fire, there is nothing about an engine failure that requires quick action to shut it down - no evidence of an engine fire, and even with an engine fire, you normally have minutes to take action - not seconds.

The one thing I keep thinking about is someone placing both fuel switches to cutoff immediately after TO. Yes, it's happened before (twice - 767s in the early 1980s), but the root causes of that mistake are understood and have been corrected. Hard to explain how it could happen (unless, God forbid, it was intentional).
787 airframe TAT probe is non-aspirated. OAT from temp sensors in the Cabin Air Compressor (CAC, electric-powered compressors/packs) inlets, blending in engine inlet T2s. I seem to recall transition to ADS TAT at some point in climbout - typical 400 ft AGL.

Very hot day, so far past breakpoint, N1 Max sensitive to TAT. Any TAT or DT latching (can't recall if) would be cleared - if at 400 ft AGL, which may not have been attained here.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Engine Failure (All)  Fuel (All)  Fuel Cutoff Switches  RAT (All)  RAT (Deployment)  V1

Alty7x7
June 13, 2025, 03:42:00 GMT
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Post: 11899963
Originally Posted by tdracer
About the only way that could happen would be some catastrophic software 'hole' in the GEnx-1B FADEC software. By design, the only thing the engine control really needs to adequately the engine is:
1) Fuel
2) Thrust lever position
Everything else is 'goodness'. The FADEC has its own dedicated (gearbox mounted) electrical generator (actually alternator), so even a 100% aircraft power loss wouldn't affect the FADECs ability to control the engine. It was right at takeoff - 'suction feed' would be more than sufficient if the aircraft fuel pumps failed, FMC and other aircraft inputs have only a secondary effect on the thrust setting, it's primarily determined the thrust lever position.
So there is no known way that a fault in the engine/aircraft interface could cause a large loss of thrust.



#3 would be the TAT and thus N1 Max on this very hot day. Nothing abrupt, but cumulative? Get hot enough and N2 limit can make hot day line steeper. But likely latched DT, which I recall was to deal with inversions. At 42C, likely used full-rated TKO. Also would be useful to know engine health, residual margins. Blast through EGT, stop at N2.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FADEC  Fuel (All)  Generators/Alternators

Alty7x7
June 14, 2025, 13:40:00 GMT
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Post: 11901495
Fuel cutoff switches

Originally Posted by MaybeItIs
My next question, again I believe not discussed, is what do the 787 Fuel Cutoff switches actually do? Obviously, they cut off the fuel supplies to the engines - pretty important in engine fire and other scenarios, but goes without saying. The real question is, what do they activate (or deactivate)? I'm assuming a simple solenoid valve, which is open when powered and closed when unpowered, but of course, there will (certainly) be Electro-Mechanical or Solid-State (Electronic) relays between the switches and the (solenoid valves).

I guess the next obvious question is, is there anything else that can turn off those Fuel Cutoff Valves - a computer condition for example. I'm assuming not, but I think it needs to be considered.

Taking each switch individually, next, since this is part of an electrical circuit, and of necessity must include Electrical Relays, there is certainly at least one and in all probability two electric Power Sources involved in this circuit. One supply which passes through the switch to activate the relay, and, I'm assuming, a second, higher current and probably higher voltage supply which drives the (solenoid?) valve.

As I see it, interrupting either supply will have the same effect - if the system is wired in the Positive-Postive sense, meaning a current through the switch causes the relay to pass a current through the (solenoid). If either of these supplies is cut, the Fuel Shutoffs will shut off the fuel. So, the question is, where do these supplies come from, and under what circumstances could they be cut off?

Sure, it looks to some (myself included) like a near simultaneous cutoff of both engines, but that doesn't have to have been caused by either of the pilots. I know there is huge redundancy built into the 787 Electrical Systems, but some of the evidence is suggesting that there was something not right with the plane's electrical system. I'm also fairly sure that there will be parts and places where certain faults can take the system down, despite the redundancy. I can't say where, but it's very difficult to design a perfect system, especially where there has to be transfers between multiple potential supplies and single actuators, motors or valves.

Having spent years repairing electrical and electronic systems, I know that the most difficult of all electrical faults are the intermittent ones. And I suspect that this is at the root of this crash. An intermittent or faulty AOA sensor has "caused" (provoked) multiple famous crashes... Can't find the one I'm looking for (pre-1980, I think) as the Max AOA issues dominate.

I can cite a very personal example, which involved the electrical supply to my house. I had several computers running 24x365 so of course, ran them off a UPS, which turned out to be a very good thing. I started to notice that at certain times, the UPS would activate - it would cut in and take over the computer loads, its alarm would go off to indicate a power fault. But the power was still on! This carried on for weeks and I initially blamed the UPS. Then, I noticed that it only happened on very hot afternoons... Long story short, the fault was caused by an electrical linesman, probably 30 years earlier, failing to tighten up a joint clamp on the phase wire to our house, across the street. Heating caused expansion then movement, and the power would momentarily go off then back on, and the UPS detected this. I note that this crash was on a hot day, and maybe this plane (which I believe was repositioned for the flight), had not been operating in such high temperatures recently, meaning the problem went unnoticed.
On a typical Boeing, fuel cutoff switch would be engine shutoff command, engine FMU valve shutoff (sometimes integrated into an engine overspeed protection system), airplane spar fuel valve and ignition exciter power.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All)  Fuel Cutoff  Fuel Cutoff Switches

Alty7x7
June 14, 2025, 13:45:00 GMT
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Post: 11901503
RAT deployment

Originally Posted by mach79
Yes but reduced power is not complete loss of thrust which leads to RAT deployment is it ?
Not clear which post you are responding to - but throttle can only command engine down to idle, whereas RAT deployment due to dual-engine failures (not the only cause of deploy) would require the engines to go sub-idle (such as flameouts that the autorelight function could not catch before falling sub-idle).

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): RAT (All)  RAT (Deployment)

Alty7x7
June 14, 2025, 14:09:00 GMT
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Post: 11901517
Max EGzt and autorelight

Originally Posted by appruser
Combining all the bits and pieces of info from this thread so far, IMO we can theoretically sequence it thus using the video from the left:

00:18 Rotation. Normal takeoff config.
00:24 Gear up starts. per Raffael with FF.
......... FR24 ADSB last transmission (71ft, 172kt) just before runway threshold. Matches with video aircraft altitude at 1/2 wingspan.
......... ? Full power flameout leaves N2 ~ 60%; Airspeed < 200k so N2 will decay to 15% in 8-10s?
......... ? Takeoff EGT of 900C needs 25-35s to fall below 250C ?
00:27 Gear up stops. per Raffael with FF. Bogies tilted.
......... ? APU starts. 20-55s to 95%N?
......... Per 787 dual-engine fail/stall memory items, PM initiates Fuel Cutoff and Run.
00:28 Visible loss of thrust. Alt ~ 200ft using aircraft wingspan as measure.
......... Matches with eyewitness "within 5-10s ... it was stuck in the air".
......... Per 787 dual-engine fail/stall memory items, PM initiates RAT Switch for 1s. Whether auto or manual, the RAT initiates.
......... RAT "bang" heard by survivor
......... RAT coming online accounts for eyewitness "lights started flickering green and white".
......... Per 787 QRH below 1000ft, PF makes no change to Main Landing Gear and flaps, aircraft pointed straight for best glide.
00:31 Descending visibly, somewhere beyond the runway threshold. Alt ~ 200ft using aircraft wingspan as measure.
......... ? Because EGT > 250C FADEC blocks fuel (T-HOT hot restart inhibit?) so no relight though N2 > 15% ?
......... 787 glide ratio between 16:1 to 25:1 with MLG down, Flaps 5. About 15-20s and 3-5000ft of glide from 200ft?
......... Some flap accounts for the ground pictures.
00:34 ? N2 has presumably decayed to 15%, FADEC flips to X-START: airspeed outside envelope? No hope of relight now.
......... PM/PF transmits Mayday?
......... Video showing RAT deployed.
00:46 APU reaches some fraction of 95%N (APU sound accounting for survivor's perception of thrust?).
00:48 Impact. 4200ft from descent start, 3990ft from airport boundary road. 17s from visible descent start.

if this is a valid sequence, the only remaining question is why the dual-engine failure at ~200ft agl?

with condolences to the families and people affected.
There should not be a max pre-start EGT limit in-flight - that should only occur on the ground for a pilot-initiated Autostart where the starting EGT redlines are lower than for in-flight.

In-flight, the Autorelight function should attempt to restart the engine as soon as a flameout is detected, and for an engine flaming out at high power it might catch it before it even goes sub-idle. Generally, Autorelight will continue attempting until some cutoff N2 at which time it will stop attempting, or if the pilot move the fuel switch to Cutoff. And while the EEC is still powered (via its own PMA) down to roughly 10% N2, the ignition exciters required for Autorelight do get their power from the airplane.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): ADSB  APU  Condolences  FADEC  FlightRadar24  Fuel (All)  Fuel Cutoff  Fuel Cutoff Switches  MAYDAY  Memory Items  RAT (All)  RAT (Deployment)  Relight

Alty7x7
June 14, 2025, 22:00:00 GMT
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Post: 11901877
TCMA

Originally Posted by BugBear
TCMA

Which side of V1 does TCMA lurk? If a pilot closes the throttles to abort, does the system allow it? After all, "too low thrust" is outside the contour....

Ya know, when every conceivable possibility (or close) has been de wormed, it"s usually something impossible, or too fearful...(Or dishonest, fraudulent, criminal ....etc ,? To include unnecessary, venal, and inappropriate)

Sledgehammer, flyswatter.... MCAS


Philosophically, it is primarily pre-V1. It prevents uncommanded high thrust when you are trying to chop the thrust on a RTO. Overthrust can generally get you off the ground post V1, as can (stating the obvious on a pilot forum) a single-engine loss post V1. So OK to shut down post V1 if still on ground.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): V1

Alty7x7
June 15, 2025, 20:23:00 GMT
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Post: 11902791
Engine failure with electrical power loss

Originally Posted by StuntPilot
We agree that there was a lack of thrust. Possibly caused by a dual engine failure. But the sharpest frames in the video do NOT show the RAT and this is counter evidence to the RAT theory. If there were substantial technical failures who knows what sounds could be generated. I find the evidence weak at best. And we immediately get into a chicken-egg problem: did some power issue of unknown nature cause an engine failure or did a dual engine failure occur, resulting in a power loss? Both are extremely unlikely and need to be backed by quality evidence. The video is not it, in my opinion. I don't know the APU intake mechanism and whether it could open after the impact.
To simplify the chicken/egg:

Tdracer earlier confirmed that an airplane electrical power loss would allow engines to keep running , because 1) engines are fully-capable of suction feed operation in takeoff envelope (if boost pumps lost), and 2) the EECs are powered by their own PMAs when running and to substantially below idle (I recall roughly 10% N2). Airplane powers the EEC for ground starts, prior to PMA coming online, and as backup to the PMA after that.

Related:

Engine igniters are powered by the aircraft. So theoretical full loss of aircraft power would disable Autorelight upon a flameout. Ignitors typically don't make the cut for most-essential battery-only loads because it would also take an engine flameout, and the airplane past V1 in ground roll can fly fine on one engine that can achieve takeoff thrust.

Autorelight is relevant - if there was a single-engine failure post V1, autorelight will attempt to relight the engine, so there is no need for a pilot to try to cycle the fuel switch to reset the EEC (potentially grabbing the wrong one), or to otherwise intervene. In such a circumstance, they need to trust their training. I've heard accounts that the most likely pilot instinct in such a situation would be to push the throttle(s) forward.

Finally - there was talk earlier about accidentally cutting the fuel switches - and it was duly noted that they have to be pulled out over the detent, so very unlikely. The same cutoff effect could be achieved with the engine fire handle(s), right behind the fuel switches on the pedestal - though they are an upward pull, so also not subject to inadvertent or accidental engagement.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): APU  Dual Engine Failure  Engine Failure (All)  Fuel (All)  Fuel Cutoff Switches  Fuel Cutoff Switches (detent)  RAT (All)  RAT (Deployment)  Relight  V1

Alty7x7
June 15, 2025, 20:28:00 GMT
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Post: 11902793
FADEC

Originally Posted by C2H5OH
Voltage fluctuation can have very nasty effects on electronics and sensors. There is a hacking technique called "voltage glitching" which makes use of these effects to trick electronics in states they are not designed for and never supposed to be.
So I wouldn't vouch for the FADECs if there was catastrophic problem with the power distribution in the aircraft.
True, for low-voltage effects. The engine PMAs are independent of the airplane electrical power distribution system. They are isolated by design.

Subjects: None

Alty7x7
June 15, 2025, 20:33:00 GMT
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Post: 11902800
TCMA

Originally Posted by C2H5OH
Why is that required for certification? Slamming the brakes and cutting fuel should do and has always sufficed in pre FADEC era. Going full power when the throttle cable brakes has been considered the safe state.
Where does that piece of software reside by the way?
It was assumed for decades that in the event of uncontrollable high thrust (UHT) that the pilot would cut the fuel. Until there was a UHT event (1999?) on the takeoff roll and the crew - in an RTO - rode it all the way down and off the runway without cutting fuel. TCMA is primarily about the RTO scenario (throttle back to idle), and after that fleet event it became a requirement for FAA Part 25 certification.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FAA  FADEC  Takeoff Roll

Alty7x7
June 15, 2025, 20:37:00 GMT
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Post: 11902802
Originally Posted by ams6110
Except as I understand it from tdracer and other posts, the FADECs are self-powered. The "FA" stands for Fully Autonomous. Whatever happens on the other electrical systems is (by design) completely isolated.
FADEC = Full-Authority Digital Engine Control

Isolation comment still applies, but 'completely' may be debatable when there are still physical connections.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FADEC

Alty7x7
July 13, 2025, 00:02:00 GMT
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Post: 11920946
CVR voice ID

Originally Posted by thnarg
Fwd EAFR records Cockpit Area Microphone only.
You can generally sort out the voices based on the earlier chatter, pre-flight and during takeoff roll. This flight was short enough to capture all of that.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Cockpit Area Audio  EAFR  Takeoff Roll

Alty7x7
July 13, 2025, 00:08:00 GMT
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Post: 11920951
Switch locking mechanism

Originally Posted by AlexGG
Could be installed with a locking mechanism disengaged.

I don't see in the report that the switches were in fact installed with the locking mechanism disengaged. Maybe I have missed it.
I was just looking into these Honeywell TL family switches for a different project. There are certain part numbers that have the locking mechanism - the ones that don't are clearly different. I didn't see anything to indicate that the locking feature was selectable or defeatable. I suspect the faulty 737 switches fron 2018 had an issue with the detent machining or maybe the loading spring - i.e. a bad batch.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All)  Fuel Cutoff Switches  Fuel Cutoff Switches (detent)  Honeywell

Alty7x7
July 13, 2025, 00:15:00 GMT
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Post: 11920953
Throttle position and fuel control switch

Originally Posted by Diff Tail Shim
The Indian AAIB are avoiding a German wings event I fear. Actually I was in a flight deck of a EJR today. Start / stop switches are so bloody obvious on the overhead as main switches. Guarded and easy to observe by all. Control switches that are not required as a normal action put away from hidden positions and visible to all. Embraer actually design systems logically. Speaking to a Captain today, he confirmed that if the the thrust levers of an EJR are beyond flight idle, engines cannot be shut down by then engine start/stop switches being turned off! You need to drag the thrust levers back to idle to shut them down. First thing I was taught as an airframe engineer converting to dual trade is that the fuel system of a airframe should not restrict an engine to receive fuel from a commanded input by the pilot. Throttle position should drive that logic. Not a lazy Boeing combined FADEC and SOV switch.
FADEC processes the fuel control switches as well as the throttle resolvers directly. Both dual-channel, separate and separated circuits. Additional logic between the two would have to be foolproof. Sometimes simpler is better, even if human actions can defeat it. There is no plausible explanation or expectation for cutting both switches three seconds after liftoff.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): AAIB (All)  AAIB (India)  FADEC  Fuel (All)  Fuel Cutoff Switches  Switch Guards

Alty7x7
July 13, 2025, 00:24:00 GMT
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Post: 11920958
Takeoff thrust loss

Originally Posted by Mrshed
On a slight tangent, I think the saddest thing about the report is learning that the plane was starting to recover.

how far off avoiding this do we think they were? 5-10 seconds?
Takeoff performance assumes a single engine loss - 50% of thrust for a twin - at V1, assuming V1 occurred at the correct time and place on the runway (before that, RTO). It is really an integral or area under the curve issue.

With about 10 seconds between to-Cutoff and back-to-Run, it.is hard to see recovery with any terrain or obstacles present. Perhaps, assuming accidental Cutoff, they were restored within a second or two, the Quick Relight could have restored thrust rapidly as the engines were still spooling down - then it is a matter of the built-in margins in the takeoff performance. But the report said the engines both were sub-idle when the Quick Relight logic would have reactivated with the restoration to Run.

I doubt it was close - up to 10 seconds with 100% thrust loss. It could easily be evaluated in a Simulator, but not sure it matters now.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All)  Fuel Cutoff Switches  Relight  V1

Alty7x7
July 13, 2025, 00:38:00 GMT
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Post: 11920965
Fire handles - lockout

Originally Posted by verticallimit
Just a thought \x97 the fire extinguisher handles perform the same function as the fuel cut-off.
Could there have been a strap /booklet or something else that accidentally got under the fire handles and activated them when one of the pilots pulled on the item?
The fire handles are not particularly well protected against something getting underneath them
Is there any information on whether the fuel cutoff switches and fire handles register as separate events on the flight data recorder, or if both are logged under a common indication, such as 'fuel switch cut off'?
My recollection is that the fire handle will be locked in this circumstance, unless the respective fuel control switch is at Cutoff. Engine fire procedure (and not before 400 ft AGL) is fuel control switch to Cutoff and then pull the fire handle (turn left for bottle 1, turn right for bottle 2).

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All)  Fuel Cutoff  Fuel Cutoff Switches

Alty7x7
July 13, 2025, 01:05:00 GMT
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Post: 11920974
FCS poles

Originally Posted by DTA
It is worth remembering that each switch has 4 poles. Think of a pole as a section of the switch. Each section controls a different function - reporting switch position to FDR, fuel cut off and so on. The chances of anything other than real physical switch movement (whether it be spilt liquid, wiring damage, loose canon plug or whatever) changing the status of all 4 sections is impossibly small. Then you have two switches.
Would not expect an FDR dedicated pole. They might pull the FCS position from the FADEC, since what really matters is what the FADEC receives as a command. I would expect two poles dedicated to the two circuits, one routed to each FADEC channel, and the others to the non-FADEC-reset-command functions.

Last edited by Alty7x7; 13th July 2025 at 01:48 .

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FADEC  FDR  Fuel (All)  Fuel Cutoff  Fuel Cutoff Switches