2025-06-22T16:37:00
permalink Post: 11908670
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
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
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
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. )
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.
https://data.ntsb.gov/Docket/Documen...ort-Master.PDF
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.
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.
2025-06-22T17:50:00
permalink Post: 11908714
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
GE Aviation: Consolidate and increase recording power with the 3254F EAFR. - https://www.geaerospace.com/sites/de...rder-3254F.pdf
As for power, this NTSB document describes the power set-up for the EAFRs
https://data.ntsb.gov/Docket/Documen...ort-Master.PDF
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.
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
GE Aviation: Consolidate and increase recording power with the 3254F EAFR. - https://www.geaerospace.com/sites/de...rder-3254F.pdf
As for power, this NTSB document describes the power set-up for the EAFRs
https://data.ntsb.gov/Docket/Documen...ort-Master.PDF
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.
Having two combined recorders is already more backup than what had previously been the norm, in addition theres the independently powered area mic going analog to the front recorder.
The common models I have checked the sheets for also provides a digital output (which is probably sent to the aft recorder via normal busses.
Having a seperate analog line going to the aft recorder would be several Kg of extra weight, and probably a substantial amount of loom design and paperwork for what is then a backup to an already redundant system.
Hence, imho why this signal only goes to the forward recorder. It is already a \xabbonus\xbb.
The power for microphone and preamp is in the >1watt range range, completely insignificant.
I am still interested in reliable information as to what is expected to be on the recorder of an aircraft which has lost the generators, what about the battery powered prinary instruments? Does some systems and the aft recorder come online with the RAT or would everything be down to the one cockpit mic? Surely not?
2025-06-26T16:01:00
permalink Post: 11911339
https://www.pib.gov.in/PressReleseDe...x?PRID=2139785
Status Report on recovery and examination of data from Black Boxes – Air India Flight AI-171
Note the front EAFR is the one with RIPS battery backup.
Status Report on recovery and examination of data from Black Boxes – Air India Flight AI-171
On the evening of 24 June 2025, the team led by DG AAIB with technical members from AAIB and NTSB began the data extraction process. The Crash Protection Module (CPM) from the front black box was safely retrieved, and on 25 June, 2025, the memory module was successfully accessed and its data downloaded at the AAIB Lab.The analysis of CVR and FDR data is underway. These efforts aim to reconstruct the sequence of events leading to the accident and identify contributing factors to enhance aviation safety and prevent future occurrences.
26 users liked this post.
2025-06-28T01:56:00
permalink Post: 11912280
The June 30, 2025 edition of Aviation Week & Space Technology (reviewed from an email with "Editors' Picks" sent to subscribers) includes an article dated June 27 by Sean Broderick, about the investigation of Air India 171. It relates some new facts or factual infomration (as well as coverage of many facts in the public domain for some time already).
One theme of the article is that the timing of release of information, in general about the investigation and specifically about data discovered in the recorder(s), appears inconsistent with other facts about the investigation. In support of this theme, the AW&ST article quotes a former NTSB investigator (with specific aircraft accident investigation experience).
The article also refers to the progress of work at the accident site (including an estimate of the number of workers involved) and the presence of aircraft accident investigation professionals from highly experienced authorities and entities (U.S. NTSB, U.K. AIB, Boieng, GE). It is pointed out - certainly with respect and diplomatic tone - that the aircraft accident investigation authority of India has relatively less experience in such matters. And that the presence of more experienced participants in the investigation (as accredited representatives, if I hopefully recall study of Annex 13 correctly) would suggest that guidance to the India authority has been available.
As the foregoing suggests the article asserts, in a thematic sense, that the timing of information release is not consistent with factual information about the investigation. (It also generally suggests that information typically is released by investigation authorities earlier within the initial 30-day time period provided for by Annex 13 .... but that generalization, while true in some cases, isn't backed up with anything specific of a factual nature.)
Mods, I hope this adds to the thread and if not please don't miss the bin when it gets tossed.
One theme of the article is that the timing of release of information, in general about the investigation and specifically about data discovered in the recorder(s), appears inconsistent with other facts about the investigation. In support of this theme, the AW&ST article quotes a former NTSB investigator (with specific aircraft accident investigation experience).
The article also refers to the progress of work at the accident site (including an estimate of the number of workers involved) and the presence of aircraft accident investigation professionals from highly experienced authorities and entities (U.S. NTSB, U.K. AIB, Boieng, GE). It is pointed out - certainly with respect and diplomatic tone - that the aircraft accident investigation authority of India has relatively less experience in such matters. And that the presence of more experienced participants in the investigation (as accredited representatives, if I hopefully recall study of Annex 13 correctly) would suggest that guidance to the India authority has been available.
As the foregoing suggests the article asserts, in a thematic sense, that the timing of information release is not consistent with factual information about the investigation. (It also generally suggests that information typically is released by investigation authorities earlier within the initial 30-day time period provided for by Annex 13 .... but that generalization, while true in some cases, isn't backed up with anything specific of a factual nature.)
Mods, I hope this adds to the thread and if not please don't miss the bin when it gets tossed.
Last edited by WillowRun 6-3; 28th Jun 2025 at 02:16 .
10 users liked this post.
2025-06-28T05:47:00
permalink Post: 11912344
In keeping with PilotDAR's request, here is some possibly useful information regarding the type of Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) likely installed in the Air India B787 (using long names etc for those who may be unfamiliar with various acronyms).
The B787 was one of the first aircraft to receive a new type of FDR/CVR, known as an Enhanced Airborne Flight Recorder (EAFR). Some detail of the time may be found here:
https://www.flightglobal.com/boeing-.../67970.article
https://www.militaryaerospace.com/po...for-boeing-787
I don't believe it's absolutely confirmed yet but earlier posts (thank you V1... Ooops et al ) indicated that the unit in question may be a GE Aviation Model 3254F, the document here gives some good detail, along with another doc from Skybrary that has some relevant information.
And this one discusses more on the 'new' ARINC-767 protocol in use with these later units.
Some broader background into ARINC's role in determining the standards applicable to aviation can be seen in this video. While it doesn't specifically cover ARINC-767 (used by the B787 EAFR) the history and associated detail is interesting and may give a little useful background:
In terms of actual data recovery I had a look around but couldn't find any video that showed this from an EAFR, however this NTSB YT link gives insight into how data was recovered from an earlier FDR unit (mounted in a Bombardier CRJ700 ). While it's different to that installed in the 787 the nature of the work and how it's carefully carried out may give some insight.
Finally, this is a link to a short report re data recovered from an EAFR in a B787-9:
https://data.ntsb.gov/Docket/Documen...ort-Master.PDF
I claim no specific knowledge here, just providing references to detail I read while trying to learn more about these newer units.
FP.
The B787 was one of the first aircraft to receive a new type of FDR/CVR, known as an Enhanced Airborne Flight Recorder (EAFR). Some detail of the time may be found here:
https://www.flightglobal.com/boeing-.../67970.article
https://www.militaryaerospace.com/po...for-boeing-787
I don't believe it's absolutely confirmed yet but earlier posts (thank you V1... Ooops et al ) indicated that the unit in question may be a GE Aviation Model 3254F, the document here gives some good detail, along with another doc from Skybrary that has some relevant information.
And this one discusses more on the 'new' ARINC-767 protocol in use with these later units.
Some broader background into ARINC's role in determining the standards applicable to aviation can be seen in this video. While it doesn't specifically cover ARINC-767 (used by the B787 EAFR) the history and associated detail is interesting and may give a little useful background:
In terms of actual data recovery I had a look around but couldn't find any video that showed this from an EAFR, however this NTSB YT link gives insight into how data was recovered from an earlier FDR unit (mounted in a Bombardier CRJ700 ). While it's different to that installed in the 787 the nature of the work and how it's carefully carried out may give some insight.
Finally, this is a link to a short report re data recovered from an EAFR in a B787-9:
https://data.ntsb.gov/Docket/Documen...ort-Master.PDF
I claim no specific knowledge here, just providing references to detail I read while trying to learn more about these newer units.
FP.
3 users liked this post.
2025-06-28T13:08:00
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.
5 users liked this post.
2025-06-28T17:04:00
permalink Post: 11912578
I am not certain on that. Remember the 737 didn't have them on the standby bus (Jeju). The NTSB doc states they're powered from the L/R 28VDC buses on the 787.
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.
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.
Last edited by D Bru; 28th Jun 2025 at 17:06 . Reason: deleting a repeat image of the elec system
5 users liked this post.
2025-06-28T19:12:00
permalink Post: 11912634
That's exactly why I would really recommend reading through the NTSB FDR report on the 2013 JA829J Boston incident helpfully posted by
EDLB
. There's potentially a wealth of data concerning a to me at least surprisingly number of 2000 of parameters written on a 787 EAFR, that is that at least if there's elec power. Even the 10 min RIPS is useless if there's no data sent from electrically shut off systems.
Auxiliary Power Unit Battery Fire Japan Airlines Boeing 787-8, JA829J Boston, Massachusetts January 7, 2013
2 users liked this post.