June 20, 2025, 17:39:00 GMT
permalink Post: 11907121
I posted my first-cut analysis in the earlier thread.
I've had a bit more time to analyse now.
Those ADS-B data points (and particularly the rate of deceleration) are EXACTLY what you would expect to see from a total engine failure at or very shortly after TAKE-OFF
(it implies a 13:1 L/D which must be pretty close for gear down and flaps 5).
It places takeoff at 700m before the runway end @ ~185kt
Based on those, max altitude was c250ft @ 140kt (or the equivalent total energy equivalent), 500m after the end of the runway.
13:1 L/D would also get you groundspeed on impact of 120kt
Do those numbers make sense?
I've had a bit more time to analyse now.
Those ADS-B data points (and particularly the rate of deceleration) are EXACTLY what you would expect to see from a total engine failure at or very shortly after TAKE-OFF
(it implies a 13:1 L/D which must be pretty close for gear down and flaps 5).
It places takeoff at 700m before the runway end @ ~185kt
Based on those, max altitude was c250ft @ 140kt (or the equivalent total energy equivalent), 500m after the end of the runway.
13:1 L/D would also get you groundspeed on impact of 120kt
Do those numbers make sense?
Exact location of house, Approx distance of 1.5 km from end of runway to crash site .
Coordinates of the camera : 23\xb003'42.3"N 72\xb037'03.5"E
The Approx Camera location of the Balcony is the Red Mark . Can the speed be calculated . Does the speed line up with the ADS B data , Does it Gain Any speed after this Balcony point ?
Co-incidently Another Witness is the Grand Mother of the Balcony Teen, she was closer to the airport as per her . she is saying that the engine was silent after it passed over (but making sound , when it was Over , RAT already deployed?? ) and made offhand comment it was gonna crash . Found that out later .
Subjects
ADSB
Engine Failure (All)
RAT (All)
RAT (Deployment)
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June 20, 2025, 20:44:00 GMT
permalink Post: 11907252
electric circuits
To explore the electrical system further see p. 86 of this document. I decided to trace out some electrical paths to equipment and do a few simple calculations.
https://fliphtml5.com/quwam/qhdw/Boo...cs_Electrical/
https://fliphtml5.com/quwam/qhdw/Boo...cs_Electrical/
The area microphone connects to both EAFRs. The EAFR are normally powered via the left and right main 28v buses.
The RAT powers the backup bus.
The main L and R 28v buses do not receive backup power.
After electric power is lost, the aft EAFR is unpowered, and the front EAFR has 10 minutes power off its internal supply.
Subjects
EAFR
RAT (All)
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June 21, 2025, 02:04:00 GMT
permalink Post: 11907425
Hello, this is my first post on pprune; as a 787 pilot I\x92m also puzzled by this accident. All seem to agree that for some reason there was a complete electrical failure and RAT deployment. With a complete electrical failure all six main fuel pumps fail. Each engine also has two mechanically driven fuel pumps. On takeoff, if there is fuel in the center tank, it will be used first, pumped by the two center tank pumps.
My airline\x92s manuals don\x92t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren\x92t able to suction feed well enough from the center tanks to sustain engine operation. If there was fuel in the center tanks, a complete electrical failure would soon lead to center tank fuel pumps failure (all fuel pumps failure as stated previously) and fuel starvation of both engines. A rescue from this situation would be an immediate selection of both center tank fuel pumps OFF (not if my airline\x92s non-normal checklists) and waiting for successful suction feed from the L and R main tanks to occur, this would take a number of seconds.
My airline\x92s manuals don\x92t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren\x92t able to suction feed well enough from the center tanks to sustain engine operation. If there was fuel in the center tanks, a complete electrical failure would soon lead to center tank fuel pumps failure (all fuel pumps failure as stated previously) and fuel starvation of both engines. A rescue from this situation would be an immediate selection of both center tank fuel pumps OFF (not if my airline\x92s non-normal checklists) and waiting for successful suction feed from the L and R main tanks to occur, this would take a number of seconds.
If you go and chat to the engineers, have a look in the IPC or MM I Ch 28, you should find a good description of the fuel boost pumps. It's been a while but I recall they are Eaton designs, the general arrangement is similar to the B777. They both have a suction feed that permits fuel feed in the event of a loss of all boost pumps. The only impact of that arises at high altitude and high thrust levels, where the engine driven fuel boost pumps may capitate and reduce the available fuel feed resulting in a lower thrust level.
Refer page 12.20.02 in the TBC's B787 FCTM, or search for "SUCTION FEED".
At sea level, full thrust will be achieved without any boost pump on the aircraft. Recall that the CWT boost pumps are known as Override boost pumps, they are feeding from the CWT when there is fuel and they are running, as the output pressure is higher from these pumps than the 2 wing boost pumps. Whether there is fuel in the CWT or not, or the CWT pumps are energised, is immaterial to whether fuel will be supplied to the engine driven fuel pumps.
Note that with BA038, the fundamental problem was blockage of wax/ice formed in the piping that blocked the FOHE, and that will cause a problem with those engines that have such architecture, but is not associated with the availability of the boost pumps themselves. Even then, the engines did not technically fail, as they have both done simultaneously with the B788 of AI 171, BA's engines were running but not able to provide significant thrust due to the FOHE blockages.
Subjects
Centre Tank
Electrical Failure
Fuel (All)
Fuel Cutoff
RAT (All)
RAT (Deployment)
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June 21, 2025, 07:13:00 GMT
permalink Post: 11907514
Hoover from the generally respected Pilot Debrief channel put up his analysis.
He analyses the point of rotation looking at the airport layout and using the video with the shack showing the aircraft rotate behind it, in that case the aircraft rotates at a reasonably normal place. That being the case what is the "cloud of particles" that appear to the left of the aircraft ?
He discounts electrical failure affecting both engines due 787 design, and fuel contamination due both engines fed from separate tanks unlikely to affect both engines at the same time.
The possibility that one engine failure occurred at a critical point in the take off and that possibly the wrong engine fuel cutoff switch was pulled.
camera angle with shack and suggested point of rotation
whats this..
He analyses the point of rotation looking at the airport layout and using the video with the shack showing the aircraft rotate behind it, in that case the aircraft rotates at a reasonably normal place. That being the case what is the "cloud of particles" that appear to the left of the aircraft ?
He discounts electrical failure affecting both engines due 787 design, and fuel contamination due both engines fed from separate tanks unlikely to affect both engines at the same time.
The possibility that one engine failure occurred at a critical point in the take off and that possibly the wrong engine fuel cutoff switch was pulled.
camera angle with shack and suggested point of rotation
whats this..
Subjects
Electrical Failure
Engine Failure (All)
Fuel (All)
Fuel Cutoff
Fuel Cutoff Switches
Pilot Debrief
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June 21, 2025, 07:37:00 GMT
permalink Post: 11907526
Rotation location triangulated by Hoover
He analyses the point of rotation looking at the airport layout and using the video with the shack showing the aircraft rotate behind it, in that case the aircraft rotates at a reasonably normal place.
camera angle with shack and suggested point of rotation
camera angle with shack and suggested point of rotation
I like that we have a picture now, and that Hoover illustrates how he made the determination.
Subjects
Pilot Debrief
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June 21, 2025, 08:37:00 GMT
permalink Post: 11907550
FR24 graphic vs FR24 data
The figures being bandied around for the speed profile during the airborne segment of the TOD look a bit odd.
Firstly, because there isn't actually any speed data in the FlightRadar24 download (and even if there were, the aircraft doesn't send Airborne Velocity packets at the same time as Airborne Position ones). This is a longstanding issue with FR24, and it means that any graphic showing speed at a given position isn't necessarily 100% accurate:
Secondly, and assuming that FR24 has calculated GS as a second-order parameter, rather than a transmitted value, the instantaneous values still don't quite match the data in the download.
It's easy to see that by correlating how far the aircraft has progressed against the data timestamps. Charting the remaining distance to the end of the runway against an arbitrary timescale starting from the first of the 8 data points looks like this:
Obviously the slope/gradient of the blue line represents the average GS between successive points. The yellow reference line corresponds to a GS of 180 kts (ignore the offset, just use the slope for comparison).
Yes, the aircraft had clearly slowed down after rotation, but the final two data points appear to show that it had stopped decelerating by the time the transponder stopped sending.
One wonders how FR24 arrived at its groundspeed values?
Firstly, because there isn't actually any speed data in the FlightRadar24 download (and even if there were, the aircraft doesn't send Airborne Velocity packets at the same time as Airborne Position ones). This is a longstanding issue with FR24, and it means that any graphic showing speed at a given position isn't necessarily 100% accurate:
Secondly, and assuming that FR24 has calculated GS as a second-order parameter, rather than a transmitted value, the instantaneous values still don't quite match the data in the download.
It's easy to see that by correlating how far the aircraft has progressed against the data timestamps. Charting the remaining distance to the end of the runway against an arbitrary timescale starting from the first of the 8 data points looks like this:
Obviously the slope/gradient of the blue line represents the average GS between successive points. The yellow reference line corresponds to a GS of 180 kts (ignore the offset, just use the slope for comparison).
Yes, the aircraft had clearly slowed down after rotation, but the final two data points appear to show that it had stopped decelerating by the time the transponder stopped sending.
One wonders how FR24 arrived at its groundspeed values?
Subjects
FlightRadar24
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June 21, 2025, 16:52:00 GMT
permalink Post: 11907864
Some assumed numbers about normal biotreatment.
https://www.biobor.com/wp-content/up...ation-IATA.pdf
If we assume 50 tonnes fuel load a 100ppmw biotreatment will be 5kg of biocide total in all tanks.
The GEnx-1B will burn about 4,5kg/s fuel each on a take off run (give or take a bit) so 9kg/s in both donks for about 20s until rotate.
So the total nominal biocide dose could be pumped in about half a second through both engines on take off power if it where not mixed at all and arrives in both engines at the same time.
This gives you an idea that with the nominal amount of biocide dose not much could have happened. If biocide is the source of this dual EFATO than an extreme overdose in addition to wrong application preventing mixture with the fuel had to be the case.
https://www.biobor.com/wp-content/up...ation-IATA.pdf
If we assume 50 tonnes fuel load a 100ppmw biotreatment will be 5kg of biocide total in all tanks.
The GEnx-1B will burn about 4,5kg/s fuel each on a take off run (give or take a bit) so 9kg/s in both donks for about 20s until rotate.
So the total nominal biocide dose could be pumped in about half a second through both engines on take off power if it where not mixed at all and arrives in both engines at the same time.
This gives you an idea that with the nominal amount of biocide dose not much could have happened. If biocide is the source of this dual EFATO than an extreme overdose in addition to wrong application preventing mixture with the fuel had to be the case.
First, the problem involves the valves (notably but not exclusively FMV and FSV), not the combustion of the product:
It is highly probable that Residue primarily composed of magnesium salts accumulated in FMV spool and FSV spool, which meter engine combustion fuel, restricted movement of spools, caused inadequate fuel metering, thereby led to engine rpm oscillation that occurred from the first flight after conducting biocide treatment.
Investigation into similar cases revealed that there were six cases reported in which both engines could not start in twin engine aircraft, and one case each in which all engines could not start in four-engine aircraft and engine thrust could not be adjusted. Any of these cases were presumed to have been caused by concentration ratio of biocide (Kathon FP1.5) that was set at higher values (about 1,000 ppm) than specified ones during biocide treatments.
From the biocide test result, it is probable that Magnesium salts contained in biocide did not dissolve in fuel, but dissolved in water contained in fuel and were accumulated in spools as crystals through the engine fuel system.
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.
Subjects
EFATO
Fuel (All)
Thread Moderation
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June 21, 2025, 19:20:00 GMT
permalink Post: 11907962
This is the type of software we are usually subject to in our everyday lives basically everywhere. Your phone, your fridge, your oven, your water heater, your car, etc. pp. ad nauseam.
In case of the Safran FADEC 3 this is not actually what we're dealing with. It uses something called an FPGA (Field Programmable Gate Array) which is a very different beast to what we are used to dealing with.
(...)
Unsurprisingly this is rather inconvenient when dealing with the real world and especially when dealing with volatile physical processes that need monitoring. Like a modern turbine engine.
Enter the FPGA.
While it is programmable what that actually means is that (at a very high level) you can build a thing called a truth table, that means a definitive mathematical mapping of input states to output states. Unlike our sequential CPU driven system an FPGA will be able to perform its entire logic every time it is asked to do so. We don't have to wait for our happy check to perform any other check.
In case of the Safran FADEC 3 this is not actually what we're dealing with. It uses something called an FPGA (Field Programmable Gate Array) which is a very different beast to what we are used to dealing with.
(...)
Unsurprisingly this is rather inconvenient when dealing with the real world and especially when dealing with volatile physical processes that need monitoring. Like a modern turbine engine.
Enter the FPGA.
While it is programmable what that actually means is that (at a very high level) you can build a thing called a truth table, that means a definitive mathematical mapping of input states to output states. Unlike our sequential CPU driven system an FPGA will be able to perform its entire logic every time it is asked to do so. We don't have to wait for our happy check to perform any other check.
... which is part of a larger Powerpoint presentation by Ansys , explaining that these products are developed with SCADE development workbench, generating either Ada or C code, and that the resulting code runs under a microkernel realtime operating system:
Now, obviously enough, a CPU can be embedded in an application-specific FPGA, but it would still execute machine code. And from my experience in other embedded systems development, current CISC or RISC CPUs have more than enough computation power to implement command and control on a modern turbofan.
Subjects
FADEC
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June 21, 2025, 21:40:00 GMT
permalink Post: 11908039
Without going round the hamsterwheel again does anyone have an actual reference for this? Because I've gone back through each of tdracer's very informative posts about this
see here
and there is a discrepancy in the two points he makes below in adjacent posts. Is tdracer talking about the same HPSOV valves? Can anyone confirm that with both AC power loss and and a temporary DC power loss there are no critical engine related shutoff valves that will fail safe (unpowered) in a closed position?
The HPSOV is made up of 2 parts which I'll call the main valve and the pilot valve. The pilot valve is actuated by a solenoid and supplied with fuel from the high-pressure side. The main valve is held shut by a spring. As long as the pilot valve is open and the high-pressure fuel pump is operating, fuel flows through the pilot valve, then pushes and holds the main valve open. The pilot valve and solenoid are 'latching,' i.e. they maintain their position until electrical power is applied. However, a certain pressure still has to be provided by the pump in order to hold the main valve open. Note that when I say 'high-pressure fuel pump,' I'm referring to the one that's mechanically driven by the engine's high-pressure shaft, not any of the electric pumps.
Note: The HPSOV is mistakenly labeled as 'PSOV' in this diagram.
Subjects
Fuel (All)
High Pressure Shutoff Valve
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June 21, 2025, 22:08:00 GMT
permalink Post: 11908056
Subjects: None
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June 21, 2025, 22:46:00 GMT
permalink Post: 11908093
Interesting perspective on FPGAs Vs some kind of RTOS, but at the end of the day it's a black box that is programmed by humans. A different architecture doesn't necessity make it "safer", the QA and assurance process will be largely the same from a functional perspective. However, if any mechanism is subject to scenarios outside of the expected norms bad things can happen.
Like the old joke goes:
Like the old joke goes:
Subjects: None
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June 22, 2025, 00:23:00 GMT
permalink Post: 11908147
It would be nice if there were some `cutaway` drawings of the centre tank,not generic` block `diagrams,and it`s venting/pressurising system..If anyone has such or knows where it can be found ,I`d be grateful..I presume it is a metal `box`,but sealed,not with an internal Bag-tank...How often are they internally inspected? Presumably by a `robot`...? Is there a `procedure`,either by aircrew or engineering to check that the `suction` system works..ever.ie after landing are all the fuel pumps turned off,(each engine /not together),or engine `run-ups` after a big `maintenance ` job...?...I have a vision of a `hissing Sid` finding a nice vent to get into..not that uncommon in the tropics...
The tank is unpressurised. It is vents to atmosphere throughout the flight. There is a fuel tank inerting system which feeds nitrogen-enriched air into the ullage (air space above the fuel). On the 787 it does this on all tanks. Other airliners only do it on the centre wing tank (and any other fuselage tanks if fitted).
Entry to the tanks once they have had fuel in, generally needs breathing apparatus once it has been in service.
Pictures of the inside of a completed 787 Centre Wing Tank aren't easy to find. This shows either the upper or lower skin with its stringers.
Subjects
Fuel (All)
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June 22, 2025, 00:26:00 GMT
permalink Post: 11908148
The Centre Wing Tank is as it says the centre of the wing. The top and bottom skins continue the aerofoil section through the fuselage, with the front and rear spars' webs forming the fore and aft ends. The inner surfaces of the top and bottom skins have spanwise 'stringers' (well that's what we called them at Airbus), which are 'I' sections attached to the inside to provide stiffness to the skins. The inner faces of the centre wing tank are the tank. There is no separate fuel bag.
The tank is unpressurised. It is vents to atmosphere throughout the flight. There is a fuel tank inerting system which feeds nitrogen-enriched air into the ullage (air space above the fuel). On the 787 it does this on all tanks. Other airliners only do it on the centre wing tank (and any other fuselage tanks if fitted).
Entry to the tanks once they have had fuel in, generally needs breathing apparatus once it has been in service.
Pictures of the inside of a completed 787 Centre Wing Tank aren't easy to find. This shows either the upper or lower skin with its stringers.
The tank is unpressurised. It is vents to atmosphere throughout the flight. There is a fuel tank inerting system which feeds nitrogen-enriched air into the ullage (air space above the fuel). On the 787 it does this on all tanks. Other airliners only do it on the centre wing tank (and any other fuselage tanks if fitted).
Entry to the tanks once they have had fuel in, generally needs breathing apparatus once it has been in service.
Pictures of the inside of a completed 787 Centre Wing Tank aren't easy to find. This shows either the upper or lower skin with its stringers.
Subjects: None
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June 22, 2025, 00:39:00 GMT
permalink Post: 11908153
Re the
SAFRAN FADEC Gen 3
: It was used on the CFM56-5B and -7B and some CF6s amongst others. Unless those engines were re-FADECed later (seems unlikely), the FADEC dates to at least the early 90s.
Safran has some pictures that looks suitably early-90s high tech:
(I wouldn't be too certain that the second image shown is this generation FADEC, as it's also shown on the Gen 4 (LEAP) FADEC page).
(I recognise that soldering iron... Metcal makes good stuff).
There is some limited detail on the air/ground system here . It shows two truck tilt and two strut compression sensors on each of the two MLGs, 8 sensors total. Truck tilt sensors give 'fast' A/G detection; truck tilt + struts gives 'slow' A/G detection. Two systems but no mention of exactly how voting works. No mention of radalt but that could be handled separately before being provided to the FADECs.
I am also now thoroughly satisfied that the FADECs have their own alternators, and that these are separate to the flight control alternators integrated into each VFSG.
Safran has some pictures that looks suitably early-90s high tech:
(I wouldn't be too certain that the second image shown is this generation FADEC, as it's also shown on the Gen 4 (LEAP) FADEC page).
(I recognise that soldering iron... Metcal makes good stuff).
There is some limited detail on the air/ground system here . It shows two truck tilt and two strut compression sensors on each of the two MLGs, 8 sensors total. Truck tilt sensors give 'fast' A/G detection; truck tilt + struts gives 'slow' A/G detection. Two systems but no mention of exactly how voting works. No mention of radalt but that could be handled separately before being provided to the FADECs.
I am also now thoroughly satisfied that the FADECs have their own alternators, and that these are separate to the flight control alternators integrated into each VFSG.
Subjects
FADEC
Generators/Alternators
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June 22, 2025, 01:08:00 GMT
permalink Post: 11908168
What boggles my mind (if my understanding is correct) is that you have redundant systems that use that redundancy not to make sure that they never accidentally shut down an engine improperly but rather to make sure they never fail to shut down an engine if even one channel thinks it should.
AFAIK
engines not returning to idle have not killed anyone yet (the engine can typically be just turned off or the fire handle pulled once the crew decides they want the engine to die) but engines shutting off at a bad time are an obvious hazard.
Subjects: None
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June 22, 2025, 03:38:00 GMT
permalink Post: 11908244
Subjects: None
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June 22, 2025, 08:33:00 GMT
permalink Post: 11908325
https://mode-s.org/1090mhz/content/ads-b/1-basics.html :
When the aircraft is on the ground (or on the water), it does not transmit altitude.
Subjects
ADSB
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June 22, 2025, 12:01:00 GMT
permalink Post: 11908441
Always possible, however since a pilot made a radio call there was some
emergency leve
l power available, which suggests the EAFR would be powered.
The Jeju recorders were okay if I recall correctly, they just had no input, was that the case?
Somoeone made a good point above about the German Wings FDR/CVR being available the next day after the aircraft was aimed at the ground like a missile. These things are built tough, as you know, this may be type specific but….
The Jeju recorders were okay if I recall correctly, they just had no input, was that the case?
Somoeone made a good point above about the German Wings FDR/CVR being available the next day after the aircraft was aimed at the ground like a missile. These things are built tough, as you know, this may be type specific but….
(from the online 2010 FCOM)
(from the maintenance training )
The 787 battery fire report says the two recorders are on the left and right 28VDC buses. I don't think those get powered on RAT by the looks of it. I would wager you get whatever is on the 235VAC 'backup bus', plus the captain's and F/O's instrument buses via C1/C2 TRUs. You won't get all of that (like the F/O's screens) because the 787 energises/de-energises specific bits of equipment, not just whole buses.
Losing recorder power looks entirely expected.
SLF Engineer (electrical - not aerospace) so no special knowledge
Perceived wisdom may be applicable in normal circumstances but not when all the holes line up.
For example I've seen it quoted many times that the engine FADECs are self powered
by the engines, the TCMAs-whether part of the FADEC or a separate unit, similarly self contained
within the engine. The perceived wisdom seems to be that there is no common single fault
which can take out both engines.
And yet we're also told that the TCMA function can only function in ground mode and receives ground-air
signals from a combination of inputs from Rad Alts and WOW sensors.
There is therefore a connection from the central EE bay to the engine.
Yes I'm sure the Rad/Alt and WOW sensor processing will use different sensors for each side and powered from different
low voltage buses.
However as an analogy, in your house your toaster in the kitchen may be on a separate circuit from the water heater in
the bathroom, each protected by a fuse at the main switchboard. In normal operation a fault in one cannot affect the other.
However a lightning strike outside the house can send much higher voltages than normal operation throughout the entire
system and trash every electrical appliance not physically disconnected at the time.
Now I'm not suggesting the aircraft was hit by lightning but FDR has proposed a single event, buildup from a water leak entering
one of the EE bays at rotate. It would be possible for one or more of the HV electrical buses to short so that all the low voltage
buses go high voltage. I have no knowledge of how the FADEC / TCMA systems connect to or process the Ground-Air signals but
there is a single fault mechanism whereby high voltage could be simultaneously and inappropriately applied to both engine control systems.
It would be unfortunate if this failure mechanism did cause power to be applied to drive the fuel shut off valve closed.
Since the likelihood is that we're looking at a low probability event then perceived wisdom about normal operations and fault modes
might not be applicable.
Perceived wisdom may be applicable in normal circumstances but not when all the holes line up.
For example I've seen it quoted many times that the engine FADECs are self powered
by the engines, the TCMAs-whether part of the FADEC or a separate unit, similarly self contained
within the engine. The perceived wisdom seems to be that there is no common single fault
which can take out both engines.
And yet we're also told that the TCMA function can only function in ground mode and receives ground-air
signals from a combination of inputs from Rad Alts and WOW sensors.
There is therefore a connection from the central EE bay to the engine.
Yes I'm sure the Rad/Alt and WOW sensor processing will use different sensors for each side and powered from different
low voltage buses.
However as an analogy, in your house your toaster in the kitchen may be on a separate circuit from the water heater in
the bathroom, each protected by a fuse at the main switchboard. In normal operation a fault in one cannot affect the other.
However a lightning strike outside the house can send much higher voltages than normal operation throughout the entire
system and trash every electrical appliance not physically disconnected at the time.
Now I'm not suggesting the aircraft was hit by lightning but FDR has proposed a single event, buildup from a water leak entering
one of the EE bays at rotate. It would be possible for one or more of the HV electrical buses to short so that all the low voltage
buses go high voltage. I have no knowledge of how the FADEC / TCMA systems connect to or process the Ground-Air signals but
there is a single fault mechanism whereby high voltage could be simultaneously and inappropriately applied to both engine control systems.
It would be unfortunate if this failure mechanism did cause power to be applied to drive the fuel shut off valve closed.
Since the likelihood is that we're looking at a low probability event then perceived wisdom about normal operations and fault modes
might not be applicable.
Weight on wheels appears to go into data concentrators that go into the common core system (i.e. data network).
Presumably there is a set of comms buses between the FADECs and the CCS to allow all the pretty indicators and EICAS alerts in the cockpit to work. The WoW sensors might flow back via that, or via dedicated digital inputs from whatever the reverse of a data concentrator is called (surely they have need for field actuators other than big motors?). Either way, left and right engine data should come from completely different computers, that are in the fwd e/e bay (or concentrators/repeaters in the wings, maybe) rather than in with the big power stuff in the aft e/e bay.
Subjects
EAFR
EICAS
Electrical Busses
FADEC
FCOM
FDR
Fuel (All)
Fuel Cutoff
MAYDAY
RAT (All)
Weight on Wheels
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June 22, 2025, 17:17:00 GMT
permalink Post: 11908653
Subjects
EAFR
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June 28, 2025, 14:08:00 GMT
permalink Post: 11912484
I suspect both recorders will contain the same data. Given the radio transmission after the loss of thrust the aircraft still had at least the emergency electrical bus powered. This should have kept both recorders online. It is however possible given the 10 minute battery backup that Boeing chose to put the the recorders on another bus but that\x92s not the norm.
This shows the centre TRUs can only power the instrument buses not the L/R DC buses, the RAT can't really power the right TRU without powering both R1/R2 buses, and powering the left TRU would require powering the left 235/115 ATU which would probably be a lot of magnetising current even if not much actual load. The contactor naming supports that.
My money is on the L/R DC buses being unpowered in RAT operation; only the CA/FO instrument buses and the 235VAC backup bus.
Subjects
Electrical Busses
NTSB
RAT (All)
TRU
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