Posts about: "RAT (All)" [Posts: 607 Pages: 31]

On this matter, your numbers fall within the range I earlier calculated from doppler shift on the rooftop video's audio, so yes the numbers make sense and, given the circumstances, are reasonably close together.

I also placed the relevant positional data (last ADSB, video source, resting site) into a GIS application and used this along with the audio stream duration to calculate average speed. Obviously it is necessary to correct the speed of sound for environmental conditions but even with this I wasn't happy with the early results I got. At about this time I came to a view that this information wasn't really going to help anyone much so didn't go any further.

From detail that may be retrieved here the FAA noted that Boeing made the following 'Request for correction' (my bolding to highlight why I quote this):

"Boeing explained that the RAT will remain operational as the airplane decelerates through the minimum RAT design speed of 120 knots, not 130 knots. Boeing expressed that the performance of the RAT was shown to meet the Boeing Model 787 requirement that specifies 120 knots as the minimum RAT design speed. We agree that the RAT will remain operational as the airplane decelerates through the minimum RAT design speed of 120 knots, not 130 knots..."

Again I'm not sure this is of any particular utility now, but is included here in the interests of ensuring as much factual data is available as possible.

FP.

FR24 has the GPS lat long position at each time - ground speed is then simply distance travelled over the time interval. The METAR quoted 25007KT and that should increase with height hence the nominal decrease in ground speed over the later ADS-B values - and probably the slight drift off the centre line once airborne.

An earlier poster defined the 787 ADS-B transmits with a height granularity of 25' - which explains the FR24 figures and I might posit that it was just about to transmit a 25' height increase when the electrical failure occurred.

The rooftop video records a nominal 14s flight time with RAT out throughout.
The CCTV video records a nominal 32s (from rotation) and subjectively the aircraft stops climbing 14s after rotation - meaning 18s of descent of which 14s are captured in the rooftop video.

If we accept the RAT is out then it must have been deployed about 12-16s after rotation, presumably immediately after the 4s of ADS-B data.

Another post referenced the RAT only supplying electrical power after 10s - I find that hard to believe, not instant obviously because there has to be some stabilisation time and startup/boot time but it would imply the LH flight instruments would only be active very late. Hopefully the RAT hydraulics would be effective quicker than that.

Or, ya know, just run the captain's instrument bus from the battery. Which unsurprisingly is exactly how it works.

When we start them in the wind tunnel they are making power very quickly. That's the whole point. The RAT GCU is a simple machine.

Is this something that you train for in your airline? Am I correct that to do this requires making the needed switch selections on the overhead panel?

Further up the thread one of the posters mentions that it is very unlikely that any crew action (checklist, QRH) would have got anywhere near to changing a fuel pump switch position.

Resubmitting following some Mod Feedback and a significant re-write. Yes, it is speculative

I have a theory that I'd like to share. It brings together various pieces of known information, along with 30+ years of my experience as an aircraft engineer that forms a plausible (IMO) explanation of what may have happened.

We Know - From the Video's and the ADSB Data:
That up to and for the first few seconds after take-off appears relatively normal.
The AC appears to lose thrust without e.g. birdstrike or other spectacular smoke /fire producing event.
That the RAT deployed.
That the pilot reported 'Thrust not achieved' [Edit - We dont 'know' this - it is heavily reported]

We can see that the AC had a relatively busy schedule in the few days prior to the accident flight, so there was no significant downtime for maintenance activities that could have caused incident.
The AC flew DEL-CDG on 11 Jun with quite a racy turnaround in CDG of 1h12m. The centre tank would have been empty at CDG on arrival, and would have been partially filled for the return CDG-DEL.
CDG-DEL Arrived 01:47 am IST. Again the Centre Tank would have been empty. But quite a bit of fuel in the wings.
8 Hrs later, at 09:48 am IST the AC departed DEL-AMD. For such a short-hop, Fuel upload would have been minimal, merely a 'topping up' if at all. Certainly nothing into the Centre Tank.
DEL That night was fairly hot and humid - 57% at 02:30, 54% at 05:30, 44% at 08:30. That wing tank fuel could have picked up a fair amount of water.

The flight DEL-AMD would have only used the wing pumps. Thus any water in that 'overnight' fuel would have been vigorously stirred and evenly suspended. At concentrations that would cause no ill-effect at all.

The AC was on the ground at AMD for 2 Hrs, from 11:17am to 1:17 pm IST. The AC would have re-fuelled, first filling up the wing tanks to the top, then filling the centre-tank to whatever quantity necessary. There was enough time for water in the wing tanks to settle out.

The B787 Fuel system has pumps in the wing tanks, and pumps in the centre tanks. The Centre Tank pumps are also known as 'override' pumps because they output a higher pressure than the wing tank pumps, thus ensuring that with all pumps running, the centre tank fuel is used first.
Should the centre tank pumps stop, due to either filure or running out of fuel to pump, the wing tank pumps then produce the pressure.
In the event that all pumps stop running (e.g. an electrical failure), the engines will suck the fuel from the wing tanks. The 'sucked' fuel comes from a dedicated pipe in each tank through the 'Suction Feed Check Valve' (so that pumped fuel doesn't just exit through the suction tube). The suction tube pickup is in a slightly different position to the wing pump pickups.

It is conceivable to me that the suction tube pickup could have been immersed in water, settled out from the fuel in the wing tanks.

Then - at start-up of the aircraft in AMD, The engines would have been supplied with fuel from the centre tank. Fresh Fuel. All OK. Wing pumps running and doing not much. But, I speculate, the suction pick-ups immersed in water. Waiting.

Start up and taxi out was all normal. Runway acceleration up to v1 appears normal. V1 - Rotate - (positive rate - Gear up? - Not my debate).
But somewhere around that time, I speculate that a significant electrical failure occurred. Enough for the RAT to deploy. Enough for the fuel pumps to stop. I'll not speculate on the cause. We know that it can occur, that's why the RAT was designed to operate.

The engines at that point were at TOGA thrust. In a significant electrical failure, the engines will keep on doing what they were last told. Keep that thrust stable. So the AC climbed for a few seconds more. The pilots did what they were trained to do for a power failure, manage that, thankfully the engines were still going well...

But there was only so much 'good' fuel in the lines. The engines sucking fuel themselves, the fuel would now be coming from the suction pickups, a different supply. A supply likely heavily water contaminated. It would take a few seconds for that contaminated fuel to actually reach the engines, but when that contaminated fuel hit, Thrust would have been significantly reduced. The EEC's would have been doing their best to maintain the thrust, firewalling the throttles would probably have little effect at that exact moment. The engines would have likely worked through that bad fuel in a shortish period of time, but a period of time that our crew did not have. A fully loaded aircraft producing less than take-off thrust, is not sustaining enough thrust for continued flight. The rest - is down to the skill of the crew in deciding exactly where to hit the ground within the very narrow range of choice they had.

The 787 wing tanks have a water scavenge system.

I'm sure this has been answered elsewhere and that I've just missed it by scrolling too fast through the backlog of (much appreciated) posts, but it's been buzzing round my mind and I wanted to try and get an answer if possible please.

Has it been confirmed that there was a dual engine shutdown and, if so, why weren't people commenting on this from the videos of the incident (if the audio was good enough to detect the RAT then surely it was good enough to tell whether the engines were running).

Thank you for your patience!

Not confirmed . What is apparent is a (substantial) loss of thrust. That's what one can say with some certainty.
That has already been discussed, and there has been abundant comment. Suggest you go back and review the original thread, and this one as well.
Thank you for your interest.

Boeing specifications say that the RAT will provide hydraulic power within 6 seconds and electrical power within 10 seconds. That would be the worst-case scenario, so it should usually be a bit less than that. Almost everything that gets electrical power from the RAT can also be powered by the main battery. So you don't have to wait for the RAT to spin up before you have instruments.

The engine-driven hydraulic pumps should still work for at least a few seconds after flameout. There's also a small amount of stored energy in the hydraulic systems even after the pumps stop. So even with that 6-second delay for the RAT, there shouldn't be any significant interruption in hydraulic power for the primary flight controls.

I read the whole threads, keeping my hands on the mousewheel so far since I'm not a pilot, just a EE / safety / systems engineer.
The hamsterwheel ist spinning a lot here, and of course it could be anything including some VHDL FPGA code line or a broken RAM cell in a cheap memory bar within the computer it was compiled with. Anything is possible, but to be honest: development processes, if followed, are usually pushing the probability to a level where it becomes pure theory. BOSCH uses FPGA+\xb5C on the brake control box of cars. They sold 100 millions of those, used 4000h each (car lifetime) without error, with less strict development process. Most errors are made on requirement level, not code.

Also, so far there is no evidence I've seen regarding the 'chicken-egg' problem, did the engines fall below idle (fuel, stall...) and this caused an electrical blackout (-> battery, RAT...) or did an EE problem cause the engines to reduce thrust (FADEC, SW bug...). And where is the common cause in all this?
There has to be a systematic error common to both engines, an external failure affecting both or a dependent fault with one affecting the other within seconds. This is the only thing I think everyone agrees here. And I refuse to beleave the external failure or dependent fault was sitting in the cockpit.
I think it is something not common to every aircraft type for the last 50 years.
So I started searching and found a candidate.

I read myself into the EE architecture of this unique 'bleed-less' design and it's megawatt powergrid since this is the part where I may be able to contribute (and I'm most curious about). Generators on the 787 are >250kW instead of <100kW each and there are two per engine instead of just one. In fact, they can go up to 516 kW and shear off the gearbox at >2200Nm (equal to >2 MW, per generator).
https://www.easa.europa.eu/en/downloads/7641/en (page 11)
So while on any other aircraft the generator is more like the dynamo on your bicycle, those generators are massive (x10).
The gearbox is connected to the HP shaft (N2) on the GEnx. I learned from Wikipedia that RR moved this gearbox to the IP shaft on the Trend 1000. And RR is happy that the A330neo Trend 7000 uses bleed air and less load on the gearbox, since this maintains stability on the HP shaft at light load (also Wikipedia).
Those generators are not in phase and frequency sync, or in other words: If you parallel them, they fight each other, it's like a short. They will almost block if this is not handled by the control box if possible (or some melting fuse blows at some point).
787 electrical system - variable frequency generators?
Somehow I find it hard to believe that they are not able to disturb the engines despite that everyone here so far is claiming that there is no way an electrical problem could influence them because FADEC has it's own supply. I read that one is sufficent to start the engine, usually both are used.
In my mind I find lot's of ways this could influence both engines simultanously. If just the BTBs on the 230V grid got some humidity (hot, no AC, water cooling...) and went up in one big arc (I think they made them semiconductor relays, too).
Could those gearboxes and engines handle 4500Nm / almost 5 MW on each HP shaft, applied within a fraction of a second without any problem?
Or if the engines were in a condition not far from compressor stall, one was stalling and 400kW load jumped from one engines generators to the other...
I did some rough estimation and one of the generators could push N2 below idle in a second or less without fuel just with its normal 250kW load (just inertia).
This is one point which is unique to this airplane model, so maybe worth a closer look.

I know that those engines are burning at >100MW at full power, but how fragile in the balance between compressor load and this one turbine stage on the HP shaft / N2, without the inertia of a 2.8 meter fan? This is just out of my background, any thermodynamic expert here?
Of course I also have no insight in SW and communication within the control boxes, how much they are talking to each other, delaying/ramping load redistribution etc. If FADEC recognizes a flameout, could it instantly command the generators to cut the load, even above idle rpm?

I would assume that some fuel contamination, valve blockade, even compressor stall would pop up slower. But such a generator could kick in within milliseconds.

As a safety guy I learned that one tends to look first at things one is familiar with (SW, HW, mechanics, pilot behaviour, maintainance, depending on one's profession) and in the end it's often the interface and dependent faults within which are not carefully considered (e.g. takeoff situation vs. thermodynamics vs. mechanics vs. power generation vs. humidity vs. generator control...) together with transient behaviour. It was the same with MCAS (safety culture vs. pilot training vs. SW design (repeated action) vs. single AOA input vs. bird strike probability close to ground vs. trim loading/blockade vs. stickshaker noise/distraction).
In fact, I was trying to find information on all those systems and directly found slides on how the engines and generators could be simulated and the power grid tested in a HIL (hardware in the loop) environment. My experience from automotive is that such simulated environments are often far from reality and HIL environment programming finished after the product is already at the customer. But of course its far easier and cheaper to apply and test faults there. But then, some programmer programms what he thinks the reaction of the engine would be.
This 'bleed-less' design was some massive change in airplane EE architecture with hugh consequences on the whole airplane design and extremely hard to fully analyze.

I'm just asking questions and hope that we all learn a lot and this was fully considered or just not an issue. It's just an aspect I found worth mentioning and not only spinning the wheel.

PS: I doubt it was TCMA. The air/ground decision is done in a different box, evaluating 5 inputs in a 1/3 and 1/2 decision according to this discussion. This is then safely sent to the FADEC (as one input) and combined with the thrust lever position and N2. But if the thrust lever position is sensed (redundant and direct) close to idle, you do not need TCMA or ground mode to expect reduced thrust.

Journos, when it comes to aviation, are morons. Kind of like my social skills, in my twenties, after a few more pints than I ought to have had.
That is what you are missing.
We thank you for the source of innocent merriment.
While I enjoyed your post, a lot, 787 has been in service for over a decade and there are over 1,000 of them doing their duty day in and day out. Yes, battery issues arose, but resolved.

Based on the mishap investigations I did, more than one of which involved fatalities, there is a whole family of maintenance / company culture errors possible that seem to me to get short shrift in the discussion here: thread number 1 and thread number 2.

But here's the problem: Air India, for very understandable reasons, isn't about to open the kimono until they are forced to.

The available video and trajectory information are quite conclusive that both engines stopped producing thrust within 12 seconds of the main wheels leaving the ground. Had partial power of any level remained, the aircraft impact would have been further away from the departure end of the runway. The NE end camera shows by using transit sightings against identifiable structures, that the failure occurred while the aircraft was still within the airport boundary area. The energy state of the aircraft at that time trades off to impact at the correct time and place.

On departure at these weights the aircraft would have some assumed temperature thrust reduction from max available on the GEnx -1B70, Unless they were carrying lead, they were around 30,000 or more below the limit weight for a flaps 5 TO. At that weight, around 440k lbs, they would have had a fair OEI climb gradient on one engine, certainly a positive gradient with the gear down, so they lost more than 50% of total thrust. There is no yaw or roll, or inputs to counter a yaw or roll moment so the aircraft was symmetrical at all times, that means losing absolutely no less than 50% of total available thrust at that point on each engine. At 50% reduction. the aircraft would have continued a positive gradient with the gear down and the flaps at the TO setting. It did not, it decelerated at around 1meter sec, or 0.1g deceleration for just maintaining level flight, but it also had to descend and that was worth around 0.05g as well. Instead of having any positive thrust margin, the guys were needing to descend to balance the decrement in thrust of around 0.15g, and that means it has negligible to no thrust from the engines. The full analysis takes more effort as the AOA has increased over the 15-20 seconds to impact, which is increasing the drag of the aircraft rapidly towards the end. For the first 5-10 seconds however, it is not such a great change, but it is still increasing.

In level flight, the aircraft would accelerate level at around 0.3-0.4g gear down with both engines running at max chuff. Lose one, and you are back to 0.05-0.1g or so. These guys had far less than one engine remaining, gravity was all that they had going for them.

To that end, there is no requirement to have the EAFR readout of the N1, N2, FF, or EGT, the video shows they had no puff going worth a darn. That is basic back of the envelope physics and anyone who does aircraft performance testing would be able to get that answer straight from the video without using a calculator, by the time they had watched the video a couple of times in replay.

I have no qualms on stating that the engines are not operating, the RAT, gear tilt are consistent with the dynamics of the aircraft. This is far simpler to determine the energy state than that of the B738W at Muan, the lack of early video required a couple of iterations of the kinetic energy of the aircraft at Muan to end up with a probable flight path, and most likely estimate of the thrust remaining for those most unfortunate souls.

regards,


FDR

OK - Fair Challenges - good post, I'll have a go at answering and simultaneously expanding my own thoughts. In fact I'm not having a go at you, I'm more working my theory....

Experience. Without wishing to dox myself, I've worked in engineering at a major airline from apprentice through (in no particular order) Line Maintenance, Heavy and Light Maintenance, to technical support and maintenance control on both Boeing and Airbus products, with various qualifications and authorisations along the way. [Hmm - Scrap this sentence?]On the day 9/11 occurred, I should have been making modifications inside a fuel tank instead of staring at the TV with mouth on the floor.
However, I would describe my experience as broad, yet shallow in respect to this incident. Some of my fleet I know every rivet. Some of my fleet I've only ever seen from a distance. I don't touch airplanes for a living any more. B787 though - is not my area of specialty. I'll dig in, but am not the expert. I am not a systems design engineer, so precise numbers and flow rates, are not what I do. But what the systems do, how they operate, what they look like, smell and taste like... yeah, I'm not a muggle. And I do have access to all the manuals and know how to use them. And - let me be clear, I am speculating. I was advancing a theory. It WILL be some flavour of wrong. The investigation will reveal all.

I Agree, Water in fuel is not a novel concept. Aircraft fuel tanks attract water - fact. How much? It varies. I've sumped tanks and got no water, I've seen drops of water beading about in the bottom of a gallon jug, I've seen gallons of water. I've been so covered in fuel I cant smell it or think straight and taken gallon after gallon not being able to tell if its fuel or water. I also agree that 57% humidity doesn't seem particularly high - its not south east Asian jungle levels - but I'm not an expert at humidity, 32Deg c at 57% humidity at 02:30 am is not going to be comfortable for me though. I looked at recent weather in DEL, and those values were at the higher end of the range.
Further, I believe the prevailing weather conditions on the ground are less important when it comes to the volume of water getting in. Fuel is cold, or gets damn cold during a 9 Hr flight. Fuel Temperature Management is an issue for our Drivers. So as the fuel is used at altitude, Air enters the tank through NACA Ducts in the outboard end of the wing. Its beneficial to maintain a slight positive pressure, amongst other things to reduce evaporation. (Added complication, there is also the Nitrogen Enrichment system due to TWA800 - but that's more about processing the air in the tank to change the properties and make it non-explosive). Then as the aircraft descends, more air enters as the air pressure increases. Its the humidity of that air in the descent that is going to determine the volume of water entering the tank and potentially the fuel. The water in the air condenses on the sides of the tank because of the cold post-flight fuel. It doesn't dissolve into the fuel, but sinks to the bottom. Ground temperature / humidity and time will likely affect how much water condenses out of that air while on the ground. There won't be a huge amount of air exchange on the ground. Likely if the AC landed at 2am, then from sunrise as the tank warmed up, there would actually be a flow out of the vents.

What Features and procedures are there to mitigate Water? I apologise if my post gave the impression that there are no mitigation processes. There are. Water is well understood in the industry.
Well for a start, Features / Design. The Aircraft has a water scavenge system. Water doesn't mix with fuel, it sinks to the bottom being about 20% denser than fuel, so at the very lowest point in the tank, the water scavenge system (Powered by the Aft Fuel Pump through a jet pump, a venturi like system) will suck up the 'fluid' at the very lowest point, where the water would collect and in Boeings words 'drip' that fluid into the path of the pump pickup inlet (but I'd describe it more as a 'squirt'). The idea being that a small amount of water injected into the fuel will be consumed by the engines harmlessly.
There is also agitation. The wing tank pumps are pretty much running constantly, from before engine startup to after engine shutdown. The pumps are quite violent to the fuel and supply more pressure then the engine could ever need. Any excess pressure is dumped right back into the tank, quite close to the pump, in a direction that would further stir up the fuel and help break up any water into suspended droplets.
This all works if there is a small amount of water in the fuel. The water scavenge pickup is right next to the pump inlet, but a bit lower. Little bits of water get managed. Looking at the pictures of the system, I'd say a couple of gallons of water would do no harm at all.
But if there was significantly more water in that tank. Guessing 10-30 + gallons, then the pump would be circulating water, or highly water rich fuel.

Then there's the suction pickup. Its in the same 'bay' as the aft fuel pump and located a little 'higher' than the pump inlet and water scavenge inlet. But also located between stringers that can separate out the settled water ( I wish I could share the pictures, but more than my job is worth ) I can imagine the suction pickup being in a pool of 'stagnant' water.

I also saw a post from Metcha about the scavenge system blocking with Algae - I don't know about that (B787 not my fleet). But possible that could aggravate things. There's also the reports of the Indian AAIB looking at the Titan Biocide incident. Its possible that might be related and could modify the theory.

Procedures - There's the (at my airline weekly I think) procedure to 'sump' the tanks. There are drain points in the tank. Valves that you can push in with a tool and fluid drains. As described earlier (and videos exist on YouTube), you drain about a gallon of fluid and examine it for water. Most often in temperate climates (my experience), there's a few 'beads' of water in the bottom of the jug, moving about like mercury. Except when there's more. Sometimes there's a clear line in the jug, half water, fuel above. And sometimes a gallon of water, that smells like fuel. You drain it until you are sure there's no water.

Could 'that much' water have condensed in the tank? Well - There's the question. I guess the basis of the theory is that on descent into DEL, the wing tanks picked up some very humid air, which settled water into the tanks through the night. Then, as the theory I posited must work, the wing pumps must have circulated and suspended that water into the fuel.
By design, the water from the CDG-DEL arrival should have been consumed in the DEL-AMD Sector. But desperately clinging to defending my theory (I appreciate this is a hole), lets assume that at DEL the pumps were running for a long time. Lets assume that the pumps allowed the water to be dispersed within the tank prior to being used through the engines. Then - in the DEL-AMD sector, the wing tanks could have picked up more water.

How much water would cause a sustained flameout? I never posited a sustained flameout. I posited a significant reduction in thrust. Listening back to the rooftop video, which at first we were all listening for evidence of RAT, there's also a rhythmic pop-pop-pop of engines struggling. I think the engines were running, albeit badly. Heavily water contaminated fuel will do that. It doesn't have to be 100% water. Just enough water to make the engine lose thrust. Your 2 gallons per second figure assumes the engine running at full flow. I'm not a figures man, I'll not challenge that, I do recall flowmeters at max thrust spin like crazy. But an engine struggling due to a high perrcentage of contamination, is that using 2 gal/sec? or just trying to? What happens if there is e.g. 20% water in the fuel?

There are also reported incidents of engine flameout / thrust reduction that have all happened at altitude. Incidents that have been recovered due to the altitude and time available. I Posited that the engines would have eventually regained full thrust once the contamination worked though. But 30 seconds of rough engine is very different at 40,000 feet than it is at 100 feet.

The theory also relies on a second part - the electrical failure. That the electrical failure causes the fuel supply to switch, a few seconds after the failure. We go, at the point of electrical failure from a pumped centre tank supply to a sucked wing tank supply. It takes time for that different fuel to reach the engine.

Ive written enough and am tired. Must stop now.

Yeah, some fuel samples make you go "Whaaat?" And then you keep draining fuel to see how much is in there, and you call up the Maintenance Control folks and tell them "We have a bad sample out here, call those idiots at the fuel farm..."
I like the cut of your jib.
Not sure if you are right, and not familiar enough with 787 to check the fuel flow logic, but a friend of mine dead-sticked a single engine trainer into a field due to water in the fuel ... 20 minutes after takeoff.
It could have happened earlier.

The equipment on RAT/battery is limited:


(from the online 2010 FCOM)


(from the maintenance training )

The 787 battery fire report says the two recorders are on the left and right 28VDC buses. I don't think those get powered on RAT by the looks of it. I would wager you get whatever is on the 235VAC 'backup bus', plus the captain's and F/O's instrument buses via C1/C2 TRUs. You won't get all of that (like the F/O's screens) because the 787 energises/de-energises specific bits of equipment, not just whole buses.

Losing recorder power looks entirely expected.


400VAC/540VDC (+-270V) is not really known for blowing past input protection in the same way as actual HV or lightning. I would expect some optocouplers and/or transformers to be both present and adequate. There's definitely some big MOVs scattered around the main 235VAC buses.

Weight on wheels appears to go into data concentrators that go into the common core system (i.e. data network).

Presumably there is a set of comms buses between the FADECs and the CCS to allow all the pretty indicators and EICAS alerts in the cockpit to work. The WoW sensors might flow back via that, or via dedicated digital inputs from whatever the reverse of a data concentrator is called (surely they have need for field actuators other than big motors?). Either way, left and right engine data should come from completely different computers, that are in the fwd e/e bay (or concentrators/repeaters in the wings, maybe) rather than in with the big power stuff in the aft e/e bay.

There is also agreement on a high probability that it stopped recording in this RAT scenario, since it is one of the things not on RAT or battery backup.
So the main information gain would probably be: Did it stop after N2 falling below idle (generator disconnect) or before (electric failure). This single second would help in the investigation and indicate what came first.
The front recorder with it's own battery would track the status / data transmission capability of all control devices over time + recording some desperate voices in the cockpit.
Since this damaged front recorder is the one thing which could solve the miracle of this crash, I would think twice before I would like to give it to a new lab as the first thing to play with.

If it has no power it won't record anything at all, like the fact that multiple electrical systems are U/S but as a limited power supply from the RAT or APU comes on-line it would have something to record. It seems to me absurd that it is not powered at all times.

From a presentation I was given when the 787 came into service, it states that the RIPS only supplies the CVR section of the fwd EAFRs. IIRC this was stated in an earlier response. If both fwd and aft EAFRs have lost power with the RAT in operation, am I correct in thinking there is no flight data to record \x96 hence only the CVR is powered?

I am starting to see the hamsterwheel references now.
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?