Semreh
2025-06-13T11:17:00
permalink Post: 11900372

Quote:

Originally Posted by The Brigadier

The Dreamliner as two identical \x93Enhanced Airborne Flight Recorders\x94, one in the tail section and one beneath the flight deck. Each one contains the CVR + FDR in one module, both have 10 minutes of battery power backup. I see reports that the one in the tail section has been recovered.

It's fine that the \x93Enhanced Airborne Flight Recorders\x94 have 10 minutes battery backup. If the bits of equipment/sensors sending data to be recorded don't have power, you will be recording 10 minutes of silence/blank data.

The concept of powering 'critical (sensor) equipment' has been floated - the problem being that it must be possible to power down malfunctioning equipment in case of fire - real or suspected. Having independent power supplies and battery back-ups all around the airframe, each with an ability to lose their magic smoke, is a poor idea.

Commercial passenger jet aircraft already have robust power supplies with multiple generators and emergency battery support. However, if one malfunctions, rather than fails completely, it can be difficult to decide which one to disable, as it can cause problems in all systems.

Subjects: CVR FDR Generators/Alternators

Semreh
2025-06-13T12:18:00
permalink Post: 11900437

Quote:

Originally Posted by Someone Somewhere

IIRC the CVR battery (in this case EAFR battery) is required to power at least the cockpit area microphone, if not the pilots' mics.

Once the RAT deployed at least some data should have come back.

It looks like you recall correctly. This skybrary PDF document "Fade Free Memory" describes the EAFR

https://skybrary.aero/sites/default/...shelf/2955.pdf

I quote from it:

Quote:

“The CVR function receives audio from three digital audio crew channels provided by the flight deck audio system and one analog audio channel from the cockpit area microphone and preamplifier,” Elliott said.

Data from the crew channels are sent to the forward EAFR and aft EAFR.
Sounds from the cockpit area microphone also are sent as a data stream to both EAFRs.
The forward EAFR, the cockpit area microphone and the preamplifier for this microphone have 10 minutes of backup power from a
forward recorder independent power supply.

That seems to indicate that as long as the forward EAFR is powered, the datastream from the cockpit area microphone will be available to both EAFRs (assuming the network to the aft EAFR is available and working).

The whole document is worth reading to glean more details.

Last edited by T28B; 13th Jun 2025 at 16:39 . Reason: Formatting assistance

Subjects: CVR EAFR RAT (All) RAT (Deployment)

Semreh
2025-06-18T08:19:00
permalink Post: 11905017

Quote:

Originally Posted by DaveReidUK

Absolutely.

If the aft EAFR ceased recording at the point (just short of the runway end) where the ADS-B and likely everything else went dark, then the extra 30 seconds of CVR recording from the forward recorder could well be crucial to the investigation.

SLF here. Please excuse some ignorant questions, and please delete if this is simply contributing to the 'noise':

1) Why would the Aft EAFR stop recording if the main battery were available?

2) The Aft EAFR has its own dedicated analogue connection from the CAM. Is it the case that other relevant audio streams are not generated and/or transported over the fibre-optic data network to the Aft EAFR when on (main) battery power alone?

Subjects: ADSB CVR EAFR

1 user liked this post.

Semreh
2025-06-22T16:37:00
permalink Post: 11908670

Quote:

Originally Posted by JustusW

In reverse order, and the first one being very speculative: The type of battery will likely be highly specific for the usecase, here rugged before anything else. Likely specialized chemistry or one of those hybrid solid state ones. Commonly they trade capacity for other features.

Regarding the recording feature, there's three types of microphone commonly used nowadays: Condenser and Ribbon type are somewhat fragile and require power to record audio while Dynamic type is basically a reverse speaker and is considered rugged. There's an off chance that a Piezzo microphone would be used here as they are basically indestructible but usually reserved for recording while in contact with a large sound transducer. My guess based on that is that we're looking at a dynamic microphone with a run of the mill preamp.
Depending on the actual electric setup this would yield a handful of different possible installations:
1) The "Cockpit Area Microphone" (hereby christened CAM because I like abbreviations) is a self contained unit consisting of a Microphone, a preamp and AD converter. This would mean while provided power the digital recording could be passed to either EAFR.
2) The CAM is a self contained unit consisting of a Microphone and a preamp. This would mean while provided power it could send an analog audio signal to the forward EAFR no problem, but would potentially struggle generating enough of a signal to be picked up by the rear EAFR.
3) The CAM is just a Microphone. This would mean it requires either no or very little power (even Condenser Mics usually require only Milliwatts) but the signal would be very hard to send over long distances and would require the EAFR to have a preamp.

In general it is audio engineering 101 to place a preamp as close to the source as possible to avoid noise. Thus I would rule out 3. It has both ups and downs to convert the analog signal to a digital signal, and there is a possibility they'd do both. In either case I am confused from an audio engineering standpoint why the rear EAFR would not pickup audio from the CAM if the forward EAFR does. Unless the rear EAFR is fed (audio) data only via BUS, which would be an interesting choice.
Also keep in mind that historically the CVR was also located in the tail section and very much received an analog signal over the entire distance. There's really no technical reason this wouldn't be possible, I routinely use far longer cables when running audio signals at concerts and those can't use compression because it would dumpster sound quality.

So, yeah, I don't understand why there would be a mismatch between the recordings of either EAFR, unless there was something else preventing all signal transmission towards the rear EAFR. The CVR in the rear has been a thing for 80 years now.

Regards,
Justus

SLF here. Mods - please delete summarily if this does not contribute to the discussion, I have no wish to waste anyones time. No 'AI' was used in the preparation of this post.

My understanding is that, as you say, the CAM has a preamp. That preamp can be powered by the RIPS that accompanies the forward EAFR.
In addition, I believe there is a single analogue connection from the CAM+preamp to the aft EAFR in addition to the analogue connection from the CAM+preamp to the forward EAFR. I believe, but am not sure,that the other flight-deck audio (headsets) is carried digitally over the fibre-optic network to the aft EAFR. The network may or may not be in operation in the event of an electrical failure: I simply don't know.

The publicly available information I can find is not stunningly clear about this.

AEROSAFETY WORLD, January 2008 - https://flightsafety.org/asw/jan08/a...47-48.pdf?dl=1

Quote:

In the 787, the EAFRs store within their CVR-function memory partitions two hours of data from four audio channels and all data link messages. \x93The CVR function receives audio from three digital audio crew channels provided by the flight deck audio system and one analog audio channel from the cockpit area microphone and preamplifier,\x94 Elliott said.( Jim Elliott, a systems/applications engineer for the manufacturer. )

GE Aviation: Consolidate and increase recording power with the 3254F EAFR. - https://www.geaerospace.com/sites/de...rder-3254F.pdf

Quote:

The Cockpit Voice Recorder function records the flight deck communications between crew members and also captures the general acoustical sound environment of the flight deck. The CVR function receives three analog audio crew channels provided by the Flight Deck Audio System and one analog audio channel from the cockpit Area Microphone and Preamplifier (AMP). The cockpit area audio and the three audio crew channels are recorded in both the forward and the aft installed EAFR recorders. The CVR recording duration is two hours minimum. Recorded audio can only be downloaded when the EAFR is off the aircraft.

As for power, this NTSB document describes the power set-up for the EAFRs

https://data.ntsb.gov/Docket/Documen...ort-Master.PDF

Quote:

Two EAFRs are installed on Boeing 787 aircraft, one forward and one aft. The forward and aft recorders are powered by the left and right 28V DC buses respectively. The forward recorder is equipped with a recorder independent power supply (RIPS) to provide backup power to the recorder for approximately 10 minutes once left DC bus power is lost. Both recorders record the same set of flight data independent of each other.

So the forward EAFR is powered from the left 28V DC bus with the possibility of being powered by the RIPS, and the aft EAFR is powered from the right 28 V DC bus.

What I have been unable to determine is whether the right and/or left 28 V DC buses are powered from the main battery in case of failure of the AC power supply. To my untrained eye, it looks like the Captain's flight displays are powered from the main battery in extremis (28 V DC - C1), but that there are various circuit breakers, that could be automated, that may or may not allow or prevent other loads (such as the F/O's flight displays (28 V DC - C2), or the aft EAFR, being supplied by the main battery, (See link to diagram). There could well be very drastic automated load shedding.

https://kb.skyhightex.com/wp-content...l-1024x640.png

If the right 28 V DC bus was unpowered for any period, it follows that the aft EAFR was not recording for that period. This would make the forward EAFR important in case of a power failure that prevented the right 28 V DC bus from providing power.

All the information that is unclear to me will be transparently clear to the crash investigators. But it seems to me that the aft EAFR will not hold data for any period that the right 28 V DC bus is not operating. Whether that applies to this incident is an open question.

Subjects: Air Worthiness Directives CVR EAFR Electrical Failure NTSB RIPS

Semreh
2025-06-22T22:07:00
permalink Post: 11908844

Originally Posted by JustusW
if ( happy == true ) {
print("I'm happy!"
}

Quote:

Originally Posted by First_Principal

Just in case it wasn't obvious, JustusW managed to make an excellent point twice in their post about FPGA's, software and bugs.

The above code has a bug, which I assume was deliberate in order to see how many of us were really reading what they had to say, and to drive that home. Well done you, it is a simple illustration of just how easy it is for issues to slip through and not be noticed.

While this simple bug would have been picked up early on by a compiler there could well be other much more esoteric and subtle bugs that could take years in operation and require a very specific set of circumstances before they trip. I make no comment or assertion that's the case here for AI 171, but it is worth bearing in mind in any search for understanding and cause.

FP.

Mmm. Yes.

To be clear, this is 'happily' executed in perl , and doesn't give the results you might expect.

if ( happy == false ) {
print("I'm happy!")
}

A FADEC might faithfully implement the logic of the design, Someone might even have spent a lot of resources to formally prov e that the FADEC logic implements the specification. The trouble is, that does not tell you that the specification is correct .

Additionally, even if the specification is correct, it is possible to be implementing the code on flawed hardware.

It is not impossible that a common set of inputs* triggered an unusual FADEC response in separate FADECs: however, not impossible does not mean that it is likely .

*For example, the FADEC could be programmed to expect an input value to be a positive integer e.g. for altitude. If the device that sends the altitude value to the FADEC sends a negative value, one of several things might happen: (1) it could be rejected as being out of range. (2) It could be replaced with the lowest possible positive value: +0 (3) It could interpret the signed integer it has been given as an unsigned integer and treat it as an unrealistically large positive value.

I am not saying this is what has happened. Getting disagreement in the format of values sent between differing systems is not an unknown problem. Software problems as a result of poor, or differing interpretations of specifications have hit many high-profile projects: such as the Mars Climate Orbiter and the Ariane 5 - so I will not say that a system that includes FADECs cannot have problems: rather, that problems are unlikely .

Subjects: FADEC

3 users liked this post.

Semreh 2025-06-13T11:17:00 permalink Post: 11900372	Quote: Originally Posted by The Brigadier The Dreamliner as two identical \x93Enhanced Airborne Flight Recorders\x94, one in the tail section and one beneath the flight deck. Each one contains the CVR + FDR in one module, both have 10 minutes of battery power backup. I see reports that the one in the tail section has been recovered. It's fine that the \x93Enhanced Airborne Flight Recorders\x94 have 10 minutes battery backup. If the bits of equipment/sensors sending data to be recorded don't have power, you will be recording 10 minutes of silence/blank data. The concept of powering 'critical (sensor) equipment' has been floated - the problem being that it must be possible to power down malfunctioning equipment in case of fire - real or suspected. Having independent power supplies and battery back-ups all around the airframe, each with an ability to lose their magic smoke, is a poor idea. Commercial passenger jet aircraft already have robust power supplies with multiple generators and emergency battery support. However, if one malfunctions, rather than fails completely, it can be difficult to decide which one to disable, as it can cause problems in all systems. Subjects: CVR FDR Generators/Alternators
Semreh 2025-06-13T12:18:00 permalink Post: 11900437	Quote: Originally Posted by Someone Somewhere IIRC the CVR battery (in this case EAFR battery) is required to power at least the cockpit area microphone, if not the pilots' mics. Once the RAT deployed at least some data should have come back. It looks like you recall correctly. This skybrary PDF document "Fade Free Memory" describes the EAFR https://skybrary.aero/sites/default/...shelf/2955.pdf I quote from it: Quote: “The CVR function receives audio from three digital audio crew channels provided by the flight deck audio system and one analog audio channel from the cockpit area microphone and preamplifier,” Elliott said. Data from the crew channels are sent to the forward EAFR and aft EAFR. Sounds from the cockpit area microphone also are sent as a data stream to both EAFRs. The forward EAFR, the cockpit area microphone and the preamplifier for this microphone have 10 minutes of backup power from a forward recorder independent power supply. That seems to indicate that as long as the forward EAFR is powered, the datastream from the cockpit area microphone will be available to both EAFRs (assuming the network to the aft EAFR is available and working). The whole document is worth reading to glean more details. Last edited by T28B; 13th Jun 2025 at 16:39 . Reason: Formatting assistance Subjects: CVR EAFR RAT (All) RAT (Deployment)
Semreh 2025-06-18T08:19:00 permalink Post: 11905017	Quote: Originally Posted by DaveReidUK Absolutely. If the aft EAFR ceased recording at the point (just short of the runway end) where the ADS-B and likely everything else went dark, then the extra 30 seconds of CVR recording from the forward recorder could well be crucial to the investigation. SLF here. Please excuse some ignorant questions, and please delete if this is simply contributing to the 'noise': 1) Why would the Aft EAFR stop recording if the main battery were available? 2) The Aft EAFR has its own dedicated analogue connection from the CAM. Is it the case that other relevant audio streams are not generated and/or transported over the fibre-optic data network to the Aft EAFR when on (main) battery power alone? Subjects: ADSB CVR EAFR 1 user liked this post.
Semreh 2025-06-22T16:37:00 permalink Post: 11908670	Quote: Originally Posted by JustusW In reverse order, and the first one being very speculative: The type of battery will likely be highly specific for the usecase, here rugged before anything else. Likely specialized chemistry or one of those hybrid solid state ones. Commonly they trade capacity for other features. Regarding the recording feature, there's three types of microphone commonly used nowadays: Condenser and Ribbon type are somewhat fragile and require power to record audio while Dynamic type is basically a reverse speaker and is considered rugged. There's an off chance that a Piezzo microphone would be used here as they are basically indestructible but usually reserved for recording while in contact with a large sound transducer. My guess based on that is that we're looking at a dynamic microphone with a run of the mill preamp. Depending on the actual electric setup this would yield a handful of different possible installations: 1) The "Cockpit Area Microphone" (hereby christened CAM because I like abbreviations) is a self contained unit consisting of a Microphone, a preamp and AD converter. This would mean while provided power the digital recording could be passed to either EAFR. 2) The CAM is a self contained unit consisting of a Microphone and a preamp. This would mean while provided power it could send an analog audio signal to the forward EAFR no problem, but would potentially struggle generating enough of a signal to be picked up by the rear EAFR. 3) The CAM is just a Microphone. This would mean it requires either no or very little power (even Condenser Mics usually require only Milliwatts) but the signal would be very hard to send over long distances and would require the EAFR to have a preamp. In general it is audio engineering 101 to place a preamp as close to the source as possible to avoid noise. Thus I would rule out 3. It has both ups and downs to convert the analog signal to a digital signal, and there is a possibility they'd do both. In either case I am confused from an audio engineering standpoint why the rear EAFR would not pickup audio from the CAM if the forward EAFR does. Unless the rear EAFR is fed (audio) data only via BUS, which would be an interesting choice. Also keep in mind that historically the CVR was also located in the tail section and very much received an analog signal over the entire distance. There's really no technical reason this wouldn't be possible, I routinely use far longer cables when running audio signals at concerts and those can't use compression because it would dumpster sound quality. So, yeah, I don't understand why there would be a mismatch between the recordings of either EAFR, unless there was something else preventing all signal transmission towards the rear EAFR. The CVR in the rear has been a thing for 80 years now. Regards, Justus SLF here. Mods - please delete summarily if this does not contribute to the discussion, I have no wish to waste anyones time. No 'AI' was used in the preparation of this post. My understanding is that, as you say, the CAM has a preamp. That preamp can be powered by the RIPS that accompanies the forward EAFR. In addition, I believe there is a single analogue connection from the CAM+preamp to the aft EAFR in addition to the analogue connection from the CAM+preamp to the forward EAFR. I believe, but am not sure,that the other flight-deck audio (headsets) is carried digitally over the fibre-optic network to the aft EAFR. The network may or may not be in operation in the event of an electrical failure: I simply don't know. The publicly available information I can find is not stunningly clear about this. AEROSAFETY WORLD, January 2008 - https://flightsafety.org/asw/jan08/a...47-48.pdf?dl=1 Quote: In the 787, the EAFRs store within their CVR-function memory partitions two hours of data from four audio channels and all data link messages. \x93The CVR function receives audio from three digital audio crew channels provided by the flight deck audio system and one analog audio channel from the cockpit area microphone and preamplifier,\x94 Elliott said.( Jim Elliott, a systems/applications engineer for the manufacturer. ) GE Aviation: Consolidate and increase recording power with the 3254F EAFR. - https://www.geaerospace.com/sites/de...rder-3254F.pdf Quote: The Cockpit Voice Recorder function records the flight deck communications between crew members and also captures the general acoustical sound environment of the flight deck. The CVR function receives three analog audio crew channels provided by the Flight Deck Audio System and one analog audio channel from the cockpit Area Microphone and Preamplifier (AMP). The cockpit area audio and the three audio crew channels are recorded in both the forward and the aft installed EAFR recorders. The CVR recording duration is two hours minimum. Recorded audio can only be downloaded when the EAFR is off the aircraft. As for power, this NTSB document describes the power set-up for the EAFRs https://data.ntsb.gov/Docket/Documen...ort-Master.PDF Quote: Two EAFRs are installed on Boeing 787 aircraft, one forward and one aft. The forward and aft recorders are powered by the left and right 28V DC buses respectively. The forward recorder is equipped with a recorder independent power supply (RIPS) to provide backup power to the recorder for approximately 10 minutes once left DC bus power is lost. Both recorders record the same set of flight data independent of each other. So the forward EAFR is powered from the left 28V DC bus with the possibility of being powered by the RIPS, and the aft EAFR is powered from the right 28 V DC bus. What I have been unable to determine is whether the right and/or left 28 V DC buses are powered from the main battery in case of failure of the AC power supply. To my untrained eye, it looks like the Captain's flight displays are powered from the main battery in extremis (28 V DC - C1), but that there are various circuit breakers, that could be automated, that may or may not allow or prevent other loads (such as the F/O's flight displays (28 V DC - C2), or the aft EAFR, being supplied by the main battery, (See link to diagram). There could well be very drastic automated load shedding. https://kb.skyhightex.com/wp-content...l-1024x640.png If the right 28 V DC bus was unpowered for any period, it follows that the aft EAFR was not recording for that period. This would make the forward EAFR important in case of a power failure that prevented the right 28 V DC bus from providing power. All the information that is unclear to me will be transparently clear to the crash investigators. But it seems to me that the aft EAFR will not hold data for any period that the right 28 V DC bus is not operating. Whether that applies to this incident is an open question. Subjects: Air Worthiness Directives CVR EAFR Electrical Failure NTSB RIPS
Semreh 2025-06-22T22:07:00 permalink Post: 11908844	Originally Posted by JustusW if ( happy == true ) { print("I'm happy!" } Quote: Originally Posted by First_Principal Just in case it wasn't obvious, JustusW managed to make an excellent point twice in their post about FPGA's, software and bugs. The above code has a bug, which I assume was deliberate in order to see how many of us were really reading what they had to say, and to drive that home. Well done you, it is a simple illustration of just how easy it is for issues to slip through and not be noticed. While this simple bug would have been picked up early on by a compiler there could well be other much more esoteric and subtle bugs that could take years in operation and require a very specific set of circumstances before they trip. I make no comment or assertion that's the case here for AI 171, but it is worth bearing in mind in any search for understanding and cause. FP. Mmm. Yes. To be clear, this is 'happily' executed in perl , and doesn't give the results you might expect. if ( happy == false ) { print("I'm happy!") } A FADEC might faithfully implement the logic of the design, Someone might even have spent a lot of resources to formally prov e that the FADEC logic implements the specification. The trouble is, that does not tell you that the specification is correct . Additionally, even if the specification is correct, it is possible to be implementing the code on flawed hardware. It is not impossible that a common set of inputs* triggered an unusual FADEC response in separate FADECs: however, not impossible does not mean that it is likely . For example, the FADEC could be programmed to expect an input value to be a positive integer e.g. for altitude. If the device that sends the altitude value to the FADEC sends a negative value, one of several things might happen: (1) it could be rejected as being out of range. (2) It could be replaced with the lowest possible positive value: +0 (3) It could interpret the signed integer it has been given as an unsigned integer and treat it as an unrealistically large positive value. I am not* saying this is what has happened. Getting disagreement in the format of values sent between differing systems is not an unknown problem. Software problems as a result of poor, or differing interpretations of specifications have hit many high-profile projects: such as the Mars Climate Orbiter and the Ariane 5 - so I will not say that a system that includes FADECs cannot have problems: rather, that problems are unlikely . Subjects: FADEC 3 users liked this post.

Posts by user "Semreh" [Posts: 5 Total up-votes: 4 Pages: 1]