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| Someone Somewhere
June 13, 2025, 11:34:00 GMT permalink Post: 11900389 |
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. Once the RAT deployed at least some data should have come back.
Now, I am probably wrong about this, but if you forget to set the altitude window to the first altitude in departure and leave it at 0 (which with some airlines the previous crew will do on shutdown) the following might possibly occur. At 50 feet LNAV engages, at 100 feet the autopilot engages, at 400 feet VNAV engages but as the altitude window is set to 0 the aircraft (on autopilot) now descends to capture 0 feet. The speed at this point in VNAV is low (max V2 + 20 kts) so, to maintain that, both thrust levers close. This, of course, would be totally unexpected and could have a startle effect. If you do not realise what has caused this you might think that there is a problem with the engines and you have very little time to deal with it. I would suggest that putting out a Mayday call at this stage is not a good use of time.
As I stated at the beginning this is probably very unlikely and may not be possible, but could be tried in a simulator. It does not explain the RAT and generally you would expect crews to shove the thrust levers fully forward. |
| Semreh
June 13, 2025, 12:18:00 GMT permalink Post: 11900437 |
https://skybrary.aero/sites/default/...shelf/2955.pdf I quote from it:
“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. The whole document is worth reading to glean more details. Last edited by T28B; 13th June 2025 at 16:39 . Reason: Formatting assistance |
| DIBO
June 16, 2025, 00:47:00 GMT permalink Post: 11903013 |
* only the forward EAFR (Enhanced airborne flight recorder) has an (external) RIPS (Recorder independent power supply) * and this RIPS provides, in addition to the forward EAFR, the cockpit area microphone and the preamplifier for this microphone with 10 minutes of backup power Pretty recently, Indian media was reporting that the forward "CVR" has been recovered. Pure speculation..but one might interpret the use of this incorrect terminology and the continued search for this second 'black box' while the rear EAFR should have been easily recovered from the mostly intact tail-section, as an indication that things aren't going as well as expected regarding FDR/CVR data-extracting (as in rear EAFR lacking the last x crucial seconds, and forward EAFR now essential for recovery of the last x-seconds of area-CVR recordings, thanks to RIPS) |
| DIBO
June 16, 2025, 00:47:00 GMT permalink Post: 11903732 |
* only the forward EAFR (Enhanced airborne flight recorder) has an (external) RIPS (Recorder independent power supply) * and this RIPS provides, in addition to the forward EAFR, the cockpit area microphone and the preamplifier for this microphone with 10 minutes of backup power Pretty recently, Indian media was reporting that the forward "CVR" has been recovered. Pure speculation..but one might interpret the use of this incorrect terminology and the continued search for this second 'black box' while the rear EAFR should have been easily recovered from the mostly intact tail-section, as an indication that things aren't going as well as expected regarding FDR/CVR data-extracting (as in rear EAFR lacking the last x crucial seconds, and forward EAFR now essential for recovery of the last x-seconds of area-CVR recordings, thanks to RIPS) |
| DIBO
June 16, 2025, 23:16:00 GMT permalink Post: 11903863 |
* only the forward EAFR (Enhanced airborne flight recorder) has an (external) RIPS (Recorder independent power supply)
* and this RIPS provides, in addition to the forward EAFR, the cockpit area microphone and the preamplifier for this microphone with 10 minutes of backup power |
| DaveReidUK
June 17, 2025, 21:29:00 GMT permalink Post: 11904679 |
the difference may lay in the content that was recorded and not so much the 2 identical EAFR's. Only the forward EAFR is connected to a dedicated backup battery (RIPS) which also provides backup power to the Cockpit Area Microphone. So in case of a major electrical power mishap, the forward - and likely (externally?) damaged - EAFR might be crucial for recovering all available CVRecordings. Hence the somewhat understandable split-up in news-reports, between FDR data (from the rear EAFR) and complete CVR recordings (from the forward).
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. |
| DaveReidUK
June 17, 2025, 21:46:00 GMT permalink Post: 11904696 |
That's an interesting possibility. The independent power supply for the forward recorder also powers the cockpit area microphone, but not the individual crew mikes, so working out who said what could well be dependent on being able to recognise the voices.
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| galaxy flyer
June 17, 2025, 23:19:00 GMT permalink Post: 11904754 |
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| Gary Brown
June 19, 2025, 09:20:00 GMT permalink Post: 11905856 |
https://www.geaerospace.com/sites/de...rder-3254F.pdf The rear EAFR doesn't have power backup. So it will only record data (both CVR and FDR) while it has normal electrical power. At what point before impact that power was lost, we do not know. |
| Kraftstoffvondesibel
June 20, 2025, 16:36:00 GMT permalink Post: 11907117 |
Regarding the Recorders, obviously nothing to do with the cause, but still:
Given:
"The forward installed EAFR along with theCockpit Area Microphone and Preamplifier are typically connected to the Recorder Independent Power Supply (RIPS), providing a backup power source for 10 minutes in the event of power interruptions."
1/in the tail, likely to not be overly damaged, but might have stopped being powered at the moment the thrust was lost. Due to digital delay, it might not have catched interesting transient data of the cause. It is too far removed from the cockpit to have independent analog feeds from microphones or other equipment. 2/ The one in the front, much more likely to have been damaged, and also more likely to be useful because it had an independent area microphone cockpit source. I have 2 questions and a speculation: Speculation: The front recorder also lost all data because the systems powered down, except it independently, and by analog direct means, powers the cockpit area microphone w/micpre and could continue recording that for a good amount of time on a small battery. This then might be the recorder recieving special treatment and delayed read out, because of the damage, and because it contains audio from the cockpit, (while the other one, might already have been read by conventional means, but doesn't contain anything of use because this was a sudden event and digital latency. Or as I assume some might speculate, the tail recoder hinted to information leaving the decision on whether to read the front recorder abroad to someone much higher up) Questions: 1/Would the recorders lose access to aircraft data streams when engine power is lost, at least temporarely making the cockpit area mic recorded by battery power on the front recorder the only source of information ? 2/The recorders only draw 20W, why is it the front have reserves only for 10 minutes? Can you even buy a battery that small giving 28VDC? Why is such a limited solution selected? (And since they have a microphone input, and the units are interchangeable why don't they just stick a few grams worth of microphone in the back of the aircraft as well, just to catch mechanical noises that could help when data input is missing. Audio sensors seems underrated.) ( For reference, This battery could power the whole recorder for an hour: https://www.batteryspace.com/custom-nimh-battery-28-8v-800mah-23wh-with-tabs.aspx ) Last edited by T28B; 20th June 2025 at 18:25 . Reason: formatting |
| JustusW
June 20, 2025, 17:45:00 GMT permalink Post: 11907155 |
1/Would the recorders lose access to aircraft data streams when engine power is lost, at least temporarely making the cockpit area mic recorded by battery power on the front recorder the only source of information ?
2/The recorders only draw 20W, why is it the front with reserves only for 10 minutes? Can you even buy a battery that small giving 28VDC? Why is such a limited solution selected? ( For reference, This battery gives about 9 times that: <url removed> ) 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 |
| Kraftstoffvondesibel
June 20, 2025, 19:10:00 GMT permalink Post: 11907217 |
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 It is likely a mems-type microphone, moving coil, ribbon or traditional condenser microphones aren’t really used outside the stage or vintage recording studios these days. But something along these lines: https://pdf.aeroexpo.online/pdf/l3-t...html#open64169 Note the dual analog and arinc digital outputs. One reason for not doing an analog line all the way to the tail would be weight, as you mention, quality or noise wouldn’t be an issue due common mode rejection. Last edited by T28B; 20th June 2025 at 19:11 . Reason: punctuation and grammar assist |
| Semreh
June 22, 2025, 16:37:00 GMT 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 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. |
| thnarg
July 11, 2025, 21:32:00 GMT permalink Post: 11919837 |
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| Kraftstoffvondesibel
July 11, 2025, 21:51:00 GMT permalink Post: 11919856 |
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| Kraftstoffvondesibel
July 11, 2025, 21:57:00 GMT permalink Post: 11919867 |
It can only know their electrical, not mechanical positions. Think about it, how would that work?
Would love to see some kind of accelerometer reading of the moment the switches went to cut off. Or even cockpit area audio. They will figure it out. |
| DaveReidUK
July 11, 2025, 22:06:00 GMT permalink Post: 11919880 |
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| Engineless
July 11, 2025, 22:07:00 GMT permalink Post: 11919881 |
A douple-pole switch. One pole used for FDR signal for the physcial switch position. The other pole for the electrical switching circuit.
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| Kraftstoffvondesibel
July 11, 2025, 23:02:00 GMT permalink Post: 11919962 |
I\x92d like to add for emphasis that we do not know what was said. We only have the investigators summary/narrative. We don\x92t know which exact words were used, or in which language they were spoken, or even which way across the command gradient those unknown words were uttered.
Having a non-english first language myself, I can find several translations from english to my own language of which all will be equally correct but fit each of the various interpretations in this thread. Someone said the data and audio must be interprered together, but we don\x92t have the audio. The other language bit os the \xabtransitioned\xbb rather than \xabmoved\xbb. We don\x92t know from the report whether it was moved. We know it electrically transitioned between states. If it was a short because of contamination, or the gate was wrongly installed or worn, cycling it back(or simply fiddling with it in high stress) explains both the sequence and time used. The only thing we know is that the switches were physically in run when found. Right next to the throttles in Idle\x85 There is also the sample rate issue raised by several. A millisecond difference can be sampled as a second difference. They might also not be sampled at the same time. Not aviation, but a automated system I owned recorded all positions and values of thousands of switches and potentiometers sequentially over about a second. The 787 is a much newer system, but processor speed isn\x92t necessarily the top priority. So maybe try and not put so much effort into analyzing words we don\x92t know and sub-second FDR data? The cockpit area microphone just might have picked up discernable clicks or plonks from the switches being moved. how about this: A nice, uncontroversial alternative to cockpit video could be a small microphone array. It would, when visualising audio data, show where and when to the millimeter a sound changes or emanates in the cockpit, any switch or mechanical fault, but not arms moving, facial expressions or who does what. It would be an easy add on/expansion to the existing battery powered area mic. They do it in large factories to pin-point loose bolts or mechanical wear well ahead of tgem needing to be changed. |
| paulross
July 12, 2025, 12:25:00 GMT permalink Post: 11920578 |
AI171 Threads by Subject
I have rebuilt the site that organises these three threads by subject here:
https://paulross.github.io/pprune-th...171/index.html
Changes:
Raise issues here https://github.com/paulross/pprune-threads/issues or PM me. |