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| EXDAC
June 20, 2025, 17:12:00 GMT permalink 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 permalink Post: 11907396 |
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 permalink Post: 11907727 |
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?
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 permalink Post: 11912544 |
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 permalink Post: 11912625 |
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 permalink Post: 11912643 |
"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 permalink Post: 11914005 |
So, 13:1 is equivalent to 4.4 degrees. Subjects: None |
| EXDAC
July 10, 2025, 12:53:00 GMT permalink Post: 11919006 |
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 permalink Post: 11919035 |
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.
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 permalink Post: 11919105 |
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 permalink 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 permalink Post: 11919993 |
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 permalink Post: 11920009 |
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 permalink Post: 11920022 |
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 permalink Post: 11920727 |
"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 permalink Post: 11921418 |
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 permalink Post: 11921482 |
- They send signals to the remote data concentrators (RDC) and the spar valve start switch relays.
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?
- 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) "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 permalink 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 permalink Post: 11922199 |
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.
Subjects: None |
| EXDAC
July 15, 2025, 18:07:00 GMT permalink Post: 11923145 |
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/ 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 |