Posts by user "EXDAC" [Posts: 46 Total up-votes: 0 Pages: 3]

EXDAC
June 20, 2025, 17:12:00 GMT
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Post: 11907144
tdracer posted - " Commanded engine cutoff - the aisle stand fuel switch sends electrical signals to the spar valve and the "High Pressure Shutoff Valve" (HPSOV) in the Fuel Metering Unit, commanding them to open/close using aircraft power. The HPSOV is solenoid controlled, and near instantaneous. The solenoid is of a 'locking' type that needs to be powered both ways (for obvious reasons, you wouldn't want a loss of electrical power to shut down the engine). The fire handle does the same thing, via different electrical paths (i.e. separate wiring)."

Search this thread for "HPSOV" if you need confirmation of the quote.

Note there are two shut off fuel valves per engine - the HPSOV and the Spar valve. Both stay where they are if power is lost.

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  High Pressure Shutoff Valve  Spar Valves

EXDAC
June 20, 2025, 23:51:00 GMT
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Post: 11907396
Originally Posted by TURIN
The fuel shut off valves are fail safe open.
Wouldn't "fail safe open" imply that the valves would open on loss of control signals or power. They don't. They stay just where they were before loss of power or control signal. If I understood tdracer's description of the HPSOV it can only be open or closed. That's not true of the spar valves which are motor driven and can stop in any intermediate position if power is lost.

The only way this is relevant to the accident is if the shut off valves had been commanded closed and then power had been lost. The valves would not open.


Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All)  Fuel Cutoff  High Pressure Shutoff Valve  Spar Valves

EXDAC
June 21, 2025, 13:01:00 GMT
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Post: 11907727
Originally Posted by Aerospace101
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?
Thanks for those two quotes. I had only used the first one in my previous reference to HPSOV operation. I have only been involved with Boeing spar valves and not any HPSOV. However, I do not see that spring shutoff when less than 300 psi is in conflict with staying open if electrical power is lost.

Hopefully tdracer will provide more detail if/when he re-joins the discussion.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): High Pressure Shutoff Valve  Spar Valves

EXDAC
June 28, 2025, 15:54:00 GMT
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Post: 11912544
Originally Posted by Innaflap
I'm pretty sure that within the 787 data is passed over the serial data protocols to a DFDAU - Digital Flight Data Acquisition Unit where it is stored as a form of database. Quite possibly XML
I am not aware of any requirement for a DFDAU (or equivalent) to store any data. I say "or equivalent" because in B717 the DFDAU is not an LRU. It is a functional partition of the VIA.

It's not clear to me that 787 EAFR even requires an external DFDAU. The GE EAFR does not -

"Provides Flight Data Acquisition function of ARINC 664 p7 data parameters – No need for a Digital Flight Data Acquisition Unit (DFDAU)."

ref https://www.geaerospace.com/sites/de...rder-3254F.pdf

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): ARINC  Digital Flight Data Acquisition Unit  EAFR  Parameters

EXDAC
June 28, 2025, 18:53:00 GMT
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Post: 11912625
Originally Posted by AAKEE
As there of corse will not be any data from shutoff systems, there still will be from systems not shut down. Basic flight parameters, I guess.
much netter than\x85nothing. Thats most certainly the background to the new regulations to battery backup.
The requirements I have seen indicate that RIPS is applicable only to CVR or the CVR function of an EAFD. If you are aware of any requirement for RIPS to support flight data recording would you please provide a reference.

FAA requirements and the discussion/changes that resulted from the initial NPRM here -

https://www.federalregister.gov/docu...er-regulations

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

EXDAC
June 28, 2025, 19:40:00 GMT
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Post: 11912643
Originally Posted by DaveReidUK
I believe the GE EAFR continues to function as both FDR and CVR for a minimum of 10 minutes following a power failure.
I was looking for connector pin data but only found this:

"The front panel contains one connector, J1, and a grounding stud. • J1 provides the main EAFR power supply, Aircraft Data Network, Ethernet Channels A and B, analog audio input, input and output discretes, and other miscellaneous signals."

If RIPS is external and the GE EAFD only has a "main power supply" pin then I agree it seems likely that the flight data function is powered by RIPS.

For RIPS to power only the CVR function I would have expected to see separate main power and RIPS power input pins. I could not find any data except the two page marketing brochure which is not definitive.

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

EXDAC
July 01, 2025, 03:35:00 GMT
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Post: 11914005
Originally Posted by MaybeItIs
Can I ask a question that I guess a few observers will also want to know? Is L/D (Lift-over-Drag?) the same as Glide Slope? I.e. for an L/D of 13, does that equate to 13 forward for 1 down? If so, even at 17, it doesn't look like it would make it.
Glide slope is expressed as an angle in degrees. L/D (lift/drag) is expressed as a ratio, such as 13:1, which is the ratio of distance flown to height lost. Glideslope = tan⁻\xb9 (D/L).

So, 13:1 is equivalent to 4.4 degrees.

Subjects: None

EXDAC
July 10, 2025, 12:53:00 GMT
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Post: 11919006
Originally Posted by moosepileit
To be less subtle- someone cuts off switches, unknown to PF and possibly PM, with throttles off idle... Would do nothing.
What is the basis for that statement? Hasn't it been stated, more than once, that thrust lever position has no influence on control of the spar valves?


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

EXDAC
July 10, 2025, 13:45:00 GMT
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Post: 11919035
Originally Posted by galaxy flyer
Just for emphasis, the fuel control switches control both the spar valve AND the shutoff inside the fuel controller at the engine. It\x92s not the spar valve the starves the engine of fuel it\x92s the HP valve. If it were only the spar valve, shut downs at the gate would take awhile.
Agreed, but that knowledge does nothing to convince anyone that TLA is not involved in the response to fuel cut off.

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  Spar Valves  TLA (Thrust Lever Angle)

EXDAC
July 10, 2025, 15:55:00 GMT
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Post: 11919105
Originally Posted by moosepileit
The "Spar valves" ahould be on the fire levers/switches. FADECS/Pylons on the cutoff switches.

That functional separation exists on MD-11 (for which I see you are rated) but not for 777 and 787. The key difference is that MD-11 fire shut off valves (equivalent to Boeing spar valves) are mechanically operated but 777 and 787 spar valves are electrically operated.

Boeing chose to have both the HP and spar valves controlled by the fire handles AND the cut off switches.

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  Spar Valves

EXDAC
July 11, 2025, 22:04:00 GMT
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Post: 11919871
Does anyone have a link to Special Airworthiness Information Bulletin (SAIB) No. NM-18-33. I did not find it in a quick search.

Last edited by Saab Dastard; 11th July 2025 at 22:26 . Reason: Removed errors

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): SAIB NM-18-33  Special Airworthiness Information Bulletin

EXDAC
July 11, 2025, 23:28:00 GMT
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Post: 11919993
Originally Posted by Torquetalk
Fuel switches are NOT toggle switches precisely because aircraft designers mitigate against brain farts involving simple switching actions.
You should ask Honeywell to correct their data sheet.

Why don't you read the data sheet for the switch series and count the number of references to "toggle switch" in the description.

https://octopart.com/datasheet/4tl83...ywell-25749542

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  Honeywell

EXDAC
July 11, 2025, 23:40:00 GMT
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Post: 11920009
Originally Posted by Torquetalk
If they only toggle one way, they aren\x92t toggle switches. Honeywell calling them that doesn\x92t help matters.
They toggle both ways.

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

EXDAC
July 11, 2025, 23:55:00 GMT
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Post: 11920022
Originally Posted by Torquetalk
If you are saying that the action required to switch on the fuel is the same as the action to switch off the fuel, a simple toggle action, then you are right.
Toggle refers to the over-center mechanism inside the switch. It is independent of the method used to guard against inadvertent operation. You could have a switch with simple sliding contacts that also had a pull to operate guard but that would not be a toggle switch.

The whole point is that toggle switches do not fall between one position and the other whether they are guarded, not guarded, or have a defective guard mechanism. It takes force on the lever to swing the internal over-center toggling mechanism to the other position.

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

EXDAC
July 12, 2025, 18:17:00 GMT
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Post: 11920727
Originally Posted by Pilot DAR
The engine \x93run/cutoff\x94 switches have a well designed locking mechanism, visible in the photo in the report as being in place to \x93run\x94. Grip by a hand is required to lift them over a lock, before they can be repositioned.
That account, which is posted as being authoritative, appears to disregard SAIB NM-18-33 which states, in part:

"In order to move the switch from one position to the other under the condition where the locking feature is engaged, it is necessary for the pilot to lift the switch up while transitioning the switch position. If the locking feature is disengaged, the switch can be moved between the two positions without lifting the switch during transition, and the switch would be exposed to the potential of inadvertent operation. Inadvertent operation of the switch could result in an unintended consequence, such as an in-flight engine shutdown.'

Since the preliminary report does not specify that this SAIB was actioned on this aircraft we do not know if it was fitted with defective switches.

In my personal opinion a defective locking feature does not explain the reported event sequence. That does not mean the switches were not defective.




Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Engine Failure (All)  Engine Shutdown  Preliminary Report  SAIB NM-18-33  Special Airworthiness Information Bulletin

EXDAC
July 13, 2025, 16:18:00 GMT
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Post: 11921418
Originally Posted by slats11
Pilots are best placed to analyze and understand accidents due to pilot error or weather or system / technical failures..
Do you really believe that line pilots are better able to understand system/technical failures than the engineers who specified, developed, and tested those systems to achieve certification? Those that developed the systems, and those who maintain them, are likely to have a far better detailed understanding of their specialist areas than any line pilot.

I concede that a line pilot is likely to have a better understanding of the aircraft systems as a whole than someone who has specialist knowledge of one, or a few, systems.

Subjects: None

EXDAC
July 13, 2025, 17:45:00 GMT
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Post: 11921482
Originally Posted by cargun
- They send signals to the remote data concentrators (RDC) and the spar valve start switch relays.
- The spar valve start switch relays use these signals to control the spar valve and the high pressure shut off valve (HPSOV) in the fuel metering unit (FMU).
(snip)
There seems to be RDC's (remote data concentrators) and CDN (common data network) between those fuel switches and the fuel valves. Is there any possibility that there may have been an electronic control module or sensor fault to generate such a signal rather than mechanical switch movements?
You do not seem to have understood what you quoted (my emphasis):

"They send signals to the remote data concentrators (RDC) and the spar valve start switch relays."

Nothing in what you quoted says or implies that the RDC is in the fuel valve control path.

Edit to add - The RDC is in the path that feeds fuel switch position to the flight data recorder. Any error in that path could make the recorded switch position disagree with the actual switch position. It cannot change the state of the fuel valves and it cannot cause the engines to stop producing thrust.

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  High Pressure Shutoff Valve  Spar Valves

EXDAC
July 14, 2025, 03:54:00 GMT
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Post: 11921843
I was involved in the flight test investigation of a system anomaly that had the potential to delay certification by months. A displays setting changed and both flight test pilots and the flight test engineer said they did not cause the change. If the flight crew didn't change the setting then some previously assumed impossible system anomaly must have caused the change. (Any of that sound familiar?)

The flight deck video clearly showed that the system setting had been changed by an inadvertent pilot action and the threat to certification was eliminated by a simple mechanical change.

Just one example of how useful flight deck video recording can be.

Subjects: None

EXDAC
July 14, 2025, 13:30:00 GMT
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Post: 11922199
Originally Posted by slats11
Dark times when many pilots will experience unpleasant intrusive thoughts that their colleague sitting beside them may do something like this. The odds may be 1 in a million, but it's still an unpleasant thing to contemplate - even if immediately rationalised away and dismissed.
Are you aware that "1 in a million" is three orders of magnitude more probable than is acceptable for a catastrophic system failure?

Subjects: None

EXDAC
July 15, 2025, 18:07:00 GMT
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Post: 11923145
Originally Posted by D Bru
Inspired by the mention in the PR about a MEL on the \x91core network\x92, I came across the polemics between Boeing and IOActive a few years ago about the alleged vulnerability of 787 core systems to outside interference (hacker attack from within a/c and/or ground), including the highly sensitive CDN module, from where also the fuel cut-off module can be accessed. It\x92s definitely not my specialty, but I thought to flag it in case someone has more informed ideas about this. To my mind it could potentially \x93outshine\x94 intentional crew action. Boeing at the time denied such options, of course. Obviously also in good faith, but who knows where we are 6 years on.

https://www.wired.com/story/boeing-7...ecurity-flaws/
I cannot read the linked article. Would you please describe what you mean by "the fuel cut-off module", preferably with reference to the related aircraft schematics showing the signal paths between the fuel switches, spar valves, and engine HPSOV.

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  High Pressure Shutoff Valve  MEL  Spar Valves