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EXDAC
June 15, 2025, 20:56:00 GMT permalink Post: 11902827 |
Edit to add - RIPS will likely maintain CVR function. |
DaveReidUK
June 15, 2025, 21:05:00 GMT permalink Post: 11902840 |
But as previously posted a recorder is only as good as the systems that provide the data to it. If those systems, or some of those systems, are not powered the data is simply not available to be recorded. You need the DFDAU (or equivalent) to be powered and you need the systems that feed data to the DFDAU (or equivalent) to be powered and operational.
Edit to add - RIPS will likely maintain CVR function. |
Innaflap
June 28, 2025, 14:25:00 GMT permalink Post: 11912515 |
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.
Any device subscribing to the AU will be getting the same information. This would include the DFDRs and whatever is used for ADS-B Happy to be corrected |
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 |
Innaflap
June 30, 2025, 14:42:00 GMT permalink Post: 11913673 |
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 \x96 No need for a Digital Flight Data Acquisition Unit (DFDAU)." ref https://www.geaerospace.com/sites/de...rder-3254F.pdf |
tdracer
July 14, 2025, 18:16:00 GMT permalink Post: 11922406 |
Two questions for
tdracer
:
1. What happens to the FADEC channels if both channels have different data / information (e.g. T/L encoders or fuel switches)? - Will the currently active channel win? - Or will the most sensible information be used (e.g. keep the engines running)? - Will there be a disagree message? - Logged to the DFDR? 2. As per the data sheet the fuel switches are 4 pole versions. 1 pole will be used for each FADEC channel. Will one (or both) of the other poles be used for the DFDR or is that information collected from the FADEC through some data bus? I know, it's very specific stuff that might only be known by the designer of the FADEC system. Again, not familiar with the specifics of the 787, but on the 747-400/-8, one pole of the fuel switch feeds EICAS - which uses it in various message logic - and sends it out to any other aircraft systems that use it. There is "Digital Flight Data Acquisition Unit) DFDAU (pronounced Daff Du) that takes all the various system digital signals, sorts them and provides them to the DFDR and QAR. The 787 has something similar to the DFDAU but I don't recall what it's called. |
ignorantAndroid
July 14, 2025, 20:32:00 GMT permalink Post: 11922481 |
Again, not familiar with the specifics of the 787, but on the 747-400/-8, one pole of the fuel switch feeds EICAS - which uses it in various message logic - and sends it out to any other aircraft systems that use it. There is "Digital Flight Data Acquisition Unit) DFDAU (pronounced Daff Du) that takes all the various system digital signals, sorts them and provides them to the DFDR and QAR. The 787 has something similar to the DFDAU but I don't recall what it's called.
The EAFRs simply sniff the required data from the CDN, so there's no DFDAU as such. For some parameters, including the fuel cutoff switches, the EAFRs also record a "Source Index." For the fuel cutoff switches, there are 4 sources numbered 1 through 4 as well as a valid/invalid flag. I don't know what the sources are, but perhaps they're the 2 RDCs plus the 2 channels of the EEC/FADEC. It appears that source 1 (the default) is not the EEC. |
GroundedSpanner
July 14, 2025, 21:09:00 GMT permalink Post: 11922503 |
Again, not familiar with the specifics of the 787, but on the 747-400/-8, one pole of the fuel switch feeds EICAS - which uses it in various message logic - and sends it out to any other aircraft systems that use it. There is "Digital Flight Data Acquisition Unit) DFDAU .... that takes all the various system digital signals, sorts them and provides them to the DFDR and QAR. The 787 has something similar to the DFDAU but I don't recall what it's called.
The other 2 contact sets feed latching relays (again driven each coil independently by dropping to GND at the switch) that then drive spar valves and reset signals to the FADEC Channels. (and more). So - for the benefit of those that hang on to the 'possibility' of electrical gremlins and 'ghost' switch signals. Each switch has 4 mechanically separated 'channels' - 2 of which do electromechanical things to the engines through separate paths, the other 2 feed through independent paths the FDR and the rest of the computer systems. The results of the electromechanical actions also feed back to the FDR. Thus the readout from the EAFR will PROVE that the switches MUST have been PHYSICALLY MOVED. And - I'm nervous to challenge you tdracer - there's quite the authority gradient and I know I'm at the bottom end, but I can't let this fly... Its 'Deefer Doo'. Fight me. ![]() |
JustusW
July 15, 2025, 10:26:00 GMT permalink Post: 11922807 |
The fuel switch discrete doesn't really get used except for engine start - if it falsely indicates shutdown (on one or both channels), the FADEC won't do anything if the engine is already running. All this will set maintenance faults - and associated EICAS Status messages (L/R ENGINE CONTROL or ENGINE C1). I doubt that would be recorded on the DFDR - it would go to the QAR but that's unlikely to survive a crash. It would also be logged in the FADEC NVM - but again no guarantee that would survive either (although when the Lauda 767 crashed due to the thrust reverser deployment, the DFDR was destroyed but the FADEC NVMs both survived - much of what we know about that crash came from the FADEC NVM.)
Again, not familiar with the specifics of the 787, but on the 747-400/-8, one pole of the fuel switch feeds EICAS - which uses it in various message logic - and sends it out to any other aircraft systems that use it. There is "Digital Flight Data Acquisition Unit) DFDAU (pronounced Daff Du) that takes all the various system digital signals, sorts them and provides them to the DFDR and QAR. The 787 has something similar to the DFDAU but I don't recall what it's called. I would assume from your statement, that if a mismatch in the NC/NO signal on the switch was detected the FADEC would not direct the Fuel Cutoff Valves to close (as far as the types you are familiar with are concerned), is that correct? The report states:
[...] at about 08:08:42 UTC [...] the Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position one after another with a time gap of 01 sec. The Engine N1 and N2 began to decrease from their take-off values as the fuel supply to the engines was cut off.
The report then states:
As per the EAFR, the Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN at about 08:08:52 UTC. [...] Thereafter at 08:08:56 UTC the Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN.
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