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AF 447 Search to resume (part2)

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AF 447 Search to resume (part2)

Old 19th May 2011, 06:38
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.. let's not go down this path, please. JT
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Old 19th May 2011, 06:38
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Thresholds and limits

Machinbird,
Depending on what came first in the loss of AF447, it might still be the result of a departure, not the cause.
I agree!
Not sure quite what you are implying.
I´m using the WX as an example to push the "a/c controllability" to the edge.
Depending on what came first in the loss of AF447, it might still be the result of a departure, not the cause.
Right!
The control design is too dependent on it as presently structured.
R&D is being done on this.

The F117 was an example of "exceeded design conditions". And there are thresholds involved.
A blast with less effect (farther) could be affordable by the System.

Last edited by Jetdriver; 19th May 2011 at 13:47.
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Old 19th May 2011, 07:05
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May I just chip in to remind folks that early in all the various AF447 threads there was considerable discussion of the two previous Air Caraibes incidents of pitot icing and Unreliable Airspeed Indication issues. In those instances (both handled successfully) the flight crews reported that a major problem was contradictory advice in the checklists over Stall Warnings, and as to where to ignore them or follow them. Broadly speaking, the PF decided to ignore a - false, as it turned out - stall warning, using his airmanship experience to fly the plane by attitude and thrust until they sorted out what information the a/c was or was not giving them.

A reasonable English summary of the incident is at:

captainchas.com & airbusforums.net • View topic - Air Caraibes precursor to AF447...

and a scan of Air Caraibe's own internal incident report (in French, but with all the checklist stuff in English) is at:

Air Caraibes Airbus A330 memo
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Old 19th May 2011, 08:10
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Thanks, agb.

So after the Air Caraibe incidents in August/September 2008 there was talk of modifiyng the checklists and procedures for the unreliable airspeed (UAS) indication case.

In AF447 AIT 1 and 2, nine months later on 1st and 4th June 2009, Airbus has acknowledged the indication of an unreliable airspeed situation on AF447 (from the ACARS data) and reminded operators to follow the relevant checklists and procedures.

Then in AF447 AIT 7 a few days ago (the "Figaro" AIT) Airbus says there is no immediate cause of concern now.

From this we might infer that either (i) Airbus have concluded that the UAS checklists and procedures are okay, despite the concerns risen from the Air Caraibe incidents. Or then (ii), the UAS procedures and checklists have been revised in the meantime. It would be interesting to know the contents of AIT 3 to 6. The third (iii) scenario is that Airbus considers the pitot tube replacement (and/or with associated changes to the warnings and ECAM) to be a sufficient remedy to the UAS handling problem.
Am I totally on the wrong track?
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Old 19th May 2011, 08:13
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Originally Posted by AGBagb
Broadly speaking, the PF decided to ignore a - false, as it turned out - stall warning, ...
As I understand it, the stall warnings were not false. They occurred at AoA's of 4.48 and 4.31 degrees, while the stall warning threshold given by the Airbus engineers is 4.2 degrees. BEA's 2nd Interim Report, 1.6.11.4 confirms that by stating that the threshold is "of the order of 4 degrees":
In clean configuration, this threshold depends, in particular, on the Mach value in such a way that it decreases when the Mach increases. It is the highest of the valid Mach values that is used to determine the threshold. If none of the three Mach values is valid, a Mach value close to zero is used. For example, it is of the order of 10° at Mach 0.3 and of 4° at Mach 0.8.
The curious thing is that the threshold did not change to 10° when the speeds became invalid.
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Old 19th May 2011, 08:21
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Some observations ..

A number of posts consider an hypothetical need for an aircraft to be able to handle whatever circumstances might be thrown at it during the course of a flight.

Unfortunately, that is not the way the system works .. any aircraft can be broken or lost if the circumstances are too extreme for the combination of aircraft and crew.

The generally excellent aviation safety record bears testimony to the soundness of the present airworthiness system.

(a) a design has to demonstrate compliance with the Design Standards before it is awarded its Type Certification.

(b) the Design Standards are based on probabilistic considerations - ie extreme events outside the required envelope may well result in the loss of an aircraft .. but such is extremely unlikely to occur.

(c) there appears to be some concern that FBW itself is a problem if the autopilot runs out of capability in an extreme event - one needs to keep in mind that the same is likely to occur with a conventional aircraft .. in the latter case it is usually the human pilot which fails to cope with the circumstances.

(d) after a significant event, such as this one, the Certification Authorities will consider whether the original aircraft certification was adequate. In some cases in the past, existing Type Certifications have been revisited and the design modified to address some in-service problem which is deemed to be a deficiency with respect to the Design Standards.

(e) after a significant event and, indeed, with consideration of routine problems, the Design Standards themselves are revisited and modified to account for available technical knowledge, state of art technical capability, and so on. One only has to compare the FAR 25 of today with that of several decades ago to see this in action.

Now, whether this mishap is the result of aircraft deficiencies, crew deficiencies, operational deficiencies, Design Standards deficiencies and so forth .. will come out of the investigation. Aspects of design and procedures may well be varied to plug whatever holes are found to exist in the dyke .. time will tell.

Think how much more difficult was the analogous situation with the early Comet losses when the investigators initially were working with very little hard evidence to go on. At least, with this mishap, the recorders will provide a very detailed story to be read by the investigators.

However, extreme events will usually/always win over technical and piloting capability and ingenuity .. which is why we try to stay away from situations which might involve an extreme event.
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Old 19th May 2011, 08:24
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On my Air Caraibes "reminder" above, and the replies.....

I certainly don't have any qualification to comment on the technical issues (and apologies if I mis-represented - from memory - stall warnings as "false", when the French actually says "inappropriate") and my initial contributions to this thread, back in the day, were purely to help with the French translation. So I hope others will chime in on the possible relevance of Air Caraibes in the light of new BEA etc info.

The Air Caraibes report (a "leaked" internal document) finished with a observation that there was to be a follow-up meeting with Airbus on whether to modify the checklists. But I'm afraid I don't know the subsequent history.
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Old 19th May 2011, 08:44
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My personal opinion is that if the control system cannot realize the full potential of the rest of the airframe, then it is a fail.
Thats a lot of failure modes to contend with.

On the one hand, the pitch up might have been a sincere attempt to protect the airframe. The control system can't query the airframe directly for its structural loads. Maybe it should in some clever way. As long as it depends on the go between - probes pitot - to deduce this info, its in a no win situation. If the pitots go kaput, all bets are off. OTOH if it wasn't the pitots icing up, some other failure would have led the control system astray. The sad fact is if the a/c inadvertently ends up in a cb all bets are off. Given that, there is still scope for improvement in Wx systems and training. IMHO.
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Old 19th May 2011, 09:54
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Air Caraibes

The link to the internal report I gave above is a little difficult to navigate, so here's a much better version:

http://www.eurocockpit.com/docs/ACA.pdf

The original discussion here in relation to AF 447 was around:

http://www.pprune.org/tech-log/376433-af447-192.html
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Old 19th May 2011, 10:06
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JD-EE wrote:
And where in the BEA reports does it declare the IRUs themselves all went unreliable at the same time. This exhausts my imagination trying to figure out how thus could happen short of a total power cut.
It doesn't. I had the same misconception which Takata helpfully corrected just recently.

In the second report, BEA said "No message present in the CFR indicates the loss of displays or of inertial information (attitudes)."

As I understand them (and again, I stand to be corrected by an expert here!), the BEA discussions of the messages (eg especially sec 1.16.2.4.1, the MAINTENANCE STATUS ADR2 explanation and the ADIRU2 (1FP2) explanation) indicate that only the air data was corrupted/divergent -- the underlying IR data was valid.
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Old 19th May 2011, 10:06
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Some new informations

LF today

Le Figaro - Flash Actu : AF447: les turbulences ''vites''

"L'équipage a réussi à contourner le nuage (de turbulences, ndlr) selon des éléments fournis par les boîtes noires" a déclaré à l'AFP une source proche du dossier sous le couvert de l'anonymat, confirmant une information d'Europe 1. Le Bureau d'enquêtes et d'analyses (BEA), organisme indépendant chargé de l'enquête technique, n'était pas disponible pour commenter cette information.


The crew managed to go round the cloud [of turbulences, note from redaction (!!! note from me)] according to elements given by the black boxes, has declared a source close to the file under anonymity, confirming an information from Europe1 (French radio). The BEA, independent body in charge of the technical inquiry, was not available to comment this information.

(...)

Repêchées début mai, les deux boîtes noires de cet Airbus A330 ont été déclarées exploitables lundi, et depuis, des informations ont commencé à fuiter dans les médias, suscitant l'irritation du BEA. Concernant la trajectoire de vol, jusqu'ici, le BEA avait relevé qu'il "existait un amas de cumulonimbus puissants", certains pouvant "être le siège d'une turbulence marquée". Il a aussi relevé que "plusieurs avions qui ont évolué avant et après le vol AF447, sensiblement à la même altitude, ont altéré leur route pour éviter des masses nuageuses". Mais il ne s'était pas exprimé sur les dernières minutes de la trajectoire de l'AF447.

(...)


Le secrétaire d'Etat aux Transport Thierry Mariani a déclaré aujourd'hui que les résultats de l'examen, permettant de déterminer les responsabilités, seraient sans doute connus "fin juin".


Junior Transport minister Thierry Mariani has declared today that the results of the examination, allowing to determine responsibilities, should doubtless be known "late June".

Pierre-Henri Gourgeon said today that there is not a unique cause etc etc.... But strangely did not really commented previous informations published by LF. Mr Mariani now speaks.

The Ile De Sein should be on site at 07h00z on 21MAY (source Marinetraffic) The latest known position is 9.7735 -22.9231 at 0952z course 227°
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Old 19th May 2011, 10:43
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Interacting with computers

First, let me apologize for my frustrated outburst of the other day - I was perhaps one beer beyond inhibition and the idea of those poor people on the ocean floor got the best of me.

Second - no one is mentioning the very most important factor here - no matter how good and competent you are, when dealing with computers that have panicked, the universal reaction is to stare at the screen in confusion. This applies to everyone - even the Apollo 11 astronauts, on the way to the lunar surface, were flummoxed by computer alarms, and if not for the intervention of the boys in the "back room", would have aborted their landing. The success of the mission was due in large part to Steve Bales, who knew the guidance computer like his hand and could make an instinctive and correct assessment of the problems Armstrong and Aldrin were facing.

It appears to me, from following these discussions, that Airbus pilots have got themselves in a situation where they are so tied to the computer, that they lose the critical ability to fly the airplane from experience and airmanship rather than from interpretation of error reports.

There is, of course, nothing wrong with computers assisting in the flight of an airplane. But they should be servants, not directors - the airplane should react as an airplane, and at any moment it should be possible to pull the plug on the flight director and fly the airplane according to aerodynamics and piloting experience, rather than by understanding various "laws" and "modes" of a particular computer system. I have very little doubt that the culprit in this terrible accident is a computer system that only understands what it is told, and falling into the sea while stalled is not part of its universe.
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Old 19th May 2011, 11:13
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Originally Posted by DeSitter
But they should be servants, not directors - the airplane should react as an airplane, and at any moment it should be possible to pull the plug on the flight director and fly the airplane according to aerodynamics and piloting experience, rather than by understanding various "laws" and "modes" of a particular computer system.
Isn't that exactly what the systems do when A/P, A/THR and "Normal Law" protections step back and say "your airplane"?
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Old 19th May 2011, 11:20
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After reading the reporting by AFP and Europe 1, I'll take the reporting by Le Figaro, which seems to have a bit more knowledge of aviation. (LF's flash story is the AFP story.)

AFP and Europe 1 offer an incomplete account. Their unnamed source states that AF447 flew around the area of turbulence, but the same source would not say anything about the last few minutes of the flight.

My interpretation of this is that FDR does not record any encounter with moderate/severe turbulence before the last few minutes. (The flight is still within the meso convective system however.)
________________

The other note of interest from French press accounts today is the claim that Airbus is pressuring the BEA to reveal the results (presumably exonerating Airbus) before the Paris Air Show.
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Old 19th May 2011, 12:42
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Air France is unhappy with Airbus.

Air France chief Pierre-Henri Gourgeon urged the media to stay calm over the causes of the 2009 Atlantic plane crash, which are expected to become clear in a matter of weeks.

"It is impossible today to draw conclusions about any kind of responsibility," he told a news conference.

"Let's wait until the experts give us a coherent message before heading off in one direction or another and speculating," Gourgeon said, dismissing questions over his future as chief executive of parent Air France-KLM.

But in remarks picked up by a microphone afterwards and relayed to journalists, Gourgeon told a colleague: "The way I answer is a bit rude, but I have to because of Airbus."
Tensions dog Air France crash investigation - Yahoo!Xtra News
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Old 19th May 2011, 12:49
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Originally Posted by HN39
Isn't that exactly what the systems do when A/P, A/THR and "Normal Law" protections step back and say "your airplane"?
- not as I read it. I read above that there is a failure mode which requires an inordinate amount of careful button pushing on an overhead panel to pass control to the pilot - no simple 'press one big button (easily to hand) and I will fly this aircraft'- or have I been mis-informed?
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Old 19th May 2011, 12:53
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JD-EE,
Am equally baffled by any suggestion of IRU problems.

Hot microphones

Can't find what RR_NDB said right now. Can tell you, though, that the clearest signal on the BAC 1-11 CVR that I heard in 1980/81 was from the hot mikes. Also occurs to me that if you play back the P1 & P2 mics simultaneously, it may provide a stereo effect. Don't know how well the mics pick up distant noises, but am confident that it's good enough to hear a pilot talking even when his headset is lying on his side console. I have a feeling that hot mikes for CVRs were advocated in the UK from the start, whereas other states were not so keen.

"Co-pilots"
This is not a pejorative term; nor does it imply inferior training (or even experience). It's a description of a role in the cockpit. To keep it simple, an A320 or B737 on a routine short-haul line-flight has two pilots, of course. The pilot-in-command is referred to as the "pilot", or P1. He has been nominated as such prior to the flight, and signs the Tech Log and loadsheet. The other pilot is the "co-pilot", or P2. When the captain "gives" a sector to the co-pilot in an enlightened airline, the captain will take over the co-pilot duties, and let the P2 take over the routine command tasks and decisions. But he/she still carries the can. We could discuss this for hours, and I don't want to teach granny to suck eggs. So I just hope this helps.
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Old 19th May 2011, 13:09
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CVR Hot Mics.

Cockpit Voice Recorder "Hot Mic", 14 CFR Parts 23, 25, 121, and 135

The NTSB indicates that the performance of CVR installations where the audio signal from the boom microphone of each flight crewmember is continuously recorded on a dedicated channel, often referred to as a "hot mic", to be far superior to the standard cockpit area microphone (CAM). This conclusion was reached after the NTSB investigated a number of accidents/incidents involving both U.S. and foreign registered airplanes equipped with CVR "hot mics". In fact, the "hot mic" has proven to be a most significant technological improvement in CVRs. This level of improvement far surpasses any technological improvement that could be achieved by state-of-the art recording or signal processing equipment.

In contrast, the quality of the audio signal recorded by the standard CAM can generally be described as poor because it requires considerable time and effort to produce a transcript. Frequently, the tape contains unintelligible dialogue that is important to the determination of causal factors. The high quality audio signal available from the "hot mic" should eliminate this problem for the most part, and at the same time, provide additional benefits, as follows:
(1) Positive crewmember identification,
(2) Redundant multichannel recordings,
(3) A potential for the evaluation of crewmember incapacitation by monitoring respiration rates, and
(4) Improved accuracy in determining which pilot was controlling the aircraft.

The Civil Aviation Authority (CAA) of the United Kingdom (UK) has required CVR "hot mic" since 1974. The UK Accident Investigation Branch's nearly 13 years of experience in analyzing CVR "hot mic" recording has prompted it to promote the adoption of standards by the international aviation community. As a result, both ICAO and EUROCAE have adopted CVR "hot mic" standards. In addition, the Board of Directors of the Air Line Pilots Association voted in May 1987 to adopt a resolution to promote the use of CVR "hot mics".

Although the benefits of CVR "hot mic" are numerous, the economic penalties are slight. In fact, most if not all major airplane manufacturers are now offering CVR "hot mics" as standard equipment, and wiring an existing microphone jack to a CVR is a relatively easy task. Therefore, a CVR "hot mic" requirement would not pose an economic penalty either for operators purchasing new equipment or retrofitting a CVR on an existing aircraft.

Cockpit Voice Recorders (CVR) and Flight Recorders
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Old 19th May 2011, 13:10
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HN39,
Isn't that exactly what the systems do when A/P, A/THR and "Normal Law" protections step back and say "your airplane"?
Not exactly.

From FCOM / ALT LAW 1 / Pitch control[INDENT]"Flight law is a load factor demand law, similar to normal law, with limited pitch rate, feedback and gains, depending on speed and configuration."

... / ALT LAW 2 / Pitch control
Identical to ALT 1 law"

Note the ambiguity: nothing is said in case Alt law 2 is due to ADR faults or disagree conditions.

We can think that in this case (ADR DISAGREE) pitch control uses a default airspeed value or default gains that mitigate the missing data. I suspect that there are potential problems in the "return to normal" sequence, i.e. when airspeed sources become asynchonously available again. Remember invalid airspeed events sometimes were very short.

Last edited by DJ77; 19th May 2011 at 20:41. Reason: Correction in italics
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Old 19th May 2011, 13:25
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Chris:

Hot microphones
Can't find what RR_NDB said right now. Can tell you, though, that the clearest signal on the BAC 1-11 CVR that I heard in 1980/81 was from the hot mikes. Also occurs to me that if you play back the P1 & P2 mics simultaneously, it may provide a stereo effect. Don't know how well the mics pick up distant noises, but am confident that it's good enough to hear a pilot talking even when his headset is lying on his side console. I have a feeling that hot mikes for CVRs were advocated in the UK from the start, whereas other states were not so keen.
The microphones on all headsets in use on commercial aircraft these days are of a type known as "noise cancelling" - this is not some electronic magic, the mic transducer is open at the front AND the back of the mic (with some mechanical delay introduced to the signal path) - when correctly positioned in front of the human mouth (within 1" or closer), the sound waves from the wearer arrive at the front of the mic first and then travel around to the rear of the unit some finite time later and correspondingly attenuated by the admitted small additional path distance (1/r sqrd law) and hence do not cancel, however sound sources at a greater distance arrive at the front and back of the mic transducer more or less simultaneously and at more or less the same volume and DO cancel. Hence "noise cancelling".

Some more explanation:
How do you make a mike directional?
Start by making an omni-directional mike. Take a mike transducer, made of a diaphragm and some hardware that changes diaphragm motion into a signal. Then put this transducer in the end of a sealed can, so that incoming sound contacts the diaphragm only on its front surface.

Sound from the front presses on the front of the diaphragm and makes a signal. Sound from the side or rear bends around to the front of the mike. This sound also presses on the front of the diaphragm and makes a signal. So the mike responds the same to sounds from all directions. In other words, it has an omni-directional polar pattern. Note that the omni mike becomes directional at high frequencies. That’s because the mike housing blocks high frequencies that arrive off-axis.

Now suppose we put some holes in the can behind the diaphragm. We carefully size these holes and add acoustic damping such as felt or foam to create an acoustic phaseshift network. It’s like an RLC circuit, which delays the signal passing through it. The holes or “rear ports” let sound into the back of the diaphragm.

How does this arrangement cancel sound from the rear?
Suppose a sound wave approaches the mike from the rear. It travels to the diaphragm by two paths: outside the mike and inside the mike through the ports. Some of the sound wave travels to the front of the diaphragm, outside the mike. The sound travel time, from the rear port location to the front, is what we call T. Some sound also enters the rear ports and is delayed. If the delay inside the mike is set the same as the delay outside the mike, sounds arrive at the front and rear of the diaphragm at the same time, in phase. Sounds push on opposite sides of the diaphragm, also in phase. The diaphragm cannot move, so sounds from the rear make a very weak signal. Rear sounds cancel out. You have created a cardioid polar pattern -also known as noise cancelling.

Sounds coming from the front do not cancel out. Why? Frontal sound waves travel to the rear ports during time T. Inside the mike, the phase-shift network further delays the sound by time T. The total delay is 2T. Since there is a big delay or phase shift between the signals at the diaphragm’s front and rear, a frontal sound makes a strong signal. High frequencies do not reach the rear of the diaphragm because they are filtered out by the rear port’s RLC filter. The cardioid mike is directional at high frequencies because its housing blocks high frequencies off-axis
Sorry for the long-winded explanation.....

However the point is that while a hot-mic recording might reveal significantly comments made 'off-PTT', the usefulness for distant cockpit sounds is doubtful. That's the job of the area mic. I do question why the area mic is not of greater bandwidth (currently limited to 6kHz I think). It is simple to find good omnidirectional mics with response out beyond 20kHz for a couple of hundred $, so cost is not the reason, at least for the mic itself.

Last edited by Jetdriver; 19th May 2011 at 13:46.
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