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.. let's not go down this path, please. JT
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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. Not sure quite what you are implying. Depending on what came first in the loss of AF447, it might still be the result of a departure, not the cause. The control design is too dependent on it as presently structured. 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. |
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 |
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? |
Originally Posted by AGBagb
Broadly speaking, the PF decided to ignore a - false, as it turned out - stall warning, ...
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. |
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. |
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. |
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. 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. |
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 |
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. 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. |
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° |
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. |
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.
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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. |
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." |
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"?
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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. |
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 |
HN39,
Isn't that exactly what the systems do when A/P, A/THR and "Normal Law" protections step back and say "your airplane"? 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. |
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. 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 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. |
DJ77;
Thanks for the added precision. Does that prevent the pilot from flying "the airplane according to aerodynamics and piloting experience"? |
And we're back again fighting amongst ourselves for the quality of the Airbus construction / philosophy / floght control laws... etc...
Desitter, First, let me apologize for my frustrated outburst of the other day - I was perhaps one beer beyond inhibition We all know how good a pilot you were and how well you could cope with airplanes that were built for virile, hairy pilots. Forget it. Just try and understand how aviation has evolved and how much safer it is now. There are hundreds of posts on the particulars of modern FBW airplanes and I suggest you read them before you'll make a complete cretin of yourself ( which hasn't happened yet) DJ77 Note the ambiguity: nothing is said if Alt law 2 is due ADR faults or disagree conditions. Your reference is only on the pitch axis which happens to have the same law in pitch whether you're in ALT 1 or 2. The Lateral modes are something else entirely as they are in Norm on ALT1 and a combination of DIR and ALT in roll and yaw. From that original mistake, your post is dead wrong and you'll have to try again. BOAC, 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? As far as this accident is concerned, and supposing that there was no return to normal on these systems, the Autopilot disengaged for a *Double ADR Fault*, the whole system reverted back to the pilots with an ALT2 FC law, which basically implies one has full control of the aircraft without protections. |
"Staying ahead of the aircraft"
Cogsim's point about staying ahead of the aircraft is important for all "drivers airframe" - in the long-gone days when I was training to become one, I was firmly told that you din't just "stay" ahead, but had to be ahead of it - and being ahead started right at the start of briefing for the sortie, or even earlier if, say, there was an early morning weather briefing and your detail was for later in the day.
That kind of "being aheadedness" also applies to sailors, and even drivers ... (in an ideal world, of course). This is just to amplify Cogsim's point and NOT to imply any reference to AF procedures, or what the crew did in this instance. |
Only one thing is certain at the moment, that is "stories" sell news-sheet.:suspect::suspect::suspect:
Time to disengage from the media feeding frenzy and await the factual report from the BEA. |
To return to an earlier point - the training capability of current simulators "beyond the normal flight envelope".
This is an area of current review within the flight simulation and training world. Firstly I should note that virtually every current FFS in use is only qualified within the bounds of the airframe manufacturer provided data package, which will cover all "normal" flight envelope bounds, however MOST will not behave realistically beyond, and will likely use simple extrapolations once you err beyond 'normal'. However it is obviously possible to model the behavior beyond the test flight data, and those with better aerodynamics understanding may be able to comment better, but the RAeS currently has an international working group titled ICATEE working on recommendations for the next generation of simulators to provide upset and extended flight envelope training. For those interested here is the mission statement/plan for ICATEE as originally defined in 2009: INTERNATIONAL COMMITTEE FOR AVIATION TRAINING IN EXTENDED ENVELOPES (ICATEE). On 3 and 4 June 2009, the Flight Simulation Group (FSG) of the Royal Aeronautical Society organized and ran a Conference entitled Flight Simulation - Towards the Edge of the Envelope. The Conference subject was related to a growing need to address the aviation safety issues arising from loss of control in flight through better training and simulation beyond what is currently covered in flight and in ground-based flight simulators. The Conference identified the need to improve aircraft upset training, the shortcomings in basic education and readiness of commercial pilots in reacting to upsets, and the technical challenges. At the conclusion of the Conference, the RAeS FSG was requested by the delegates to form a Committee to explore the formation of an International Working Group (IWG) to identify follow-on steps and to invite participation from other interested parties. The FSG has considered this request and subject to Society approval plans to proceed with the leadership of this Working Group which we have titled the International Committee for Aviation Training in Extended Envelopes (ICATEE). The ICATEE objectives can be stated as follows: -To be a body independent of national, corporate or factional interests, amalgamating information on the subject matter -To identify the problem and recommend prioritization for remedial action -To identify and help qualify current processes and methodologies -To collect data on enhanced envelope maneuvers -To interact with research concerning improved training in extended flight envelopes -To identify and recommend best practices -To identify future related research activities -To support the implementation of regulatory guidelines or updates for enhanced training The main activities of the Working Group will be: - to review current practice in extended envelope training - identify the main shortcomings - identify the data and training media requirements and further research required - recommend the areas that need immediate improvement in flight training - examine essential and desirable training elements - suggest how standards can be established. The FSG has established an ICATEE steering group of FSG members consisting of Sunjoo Advani (chair), Gordon Woolley (co-chair) and Peter Tharp (co-chair). This group will set up and confirm the plan of the Working Group, assign tasks, request the support of the participants to fulfill these responsibilities, establish the time lines,and report the findings outside the group. It will also prepare the Committee’s Constitution and Terms of Reference. The RAeS Flight Operations Group has been invited to participate and the Human Factors and Air Transport Groups will also be kept updated with progress. Participants in the group will be expected to finance their own involvement. No funding will be requested or required from the Society. It is the intention to present the findings of the ICATEE at an RAeS Conference in the first half of 2011. The first form of dissemination of the information gained within the Working Group will be through the Royal Aeronautical Society FSG meetings and conferences. It is proposed that several channels be established in order to disseminate the information from the Working Group: -a web-based forum through the RaeS FSG website -a limited number of meetings -presentation at the appropriate conferences (e.g. FSG, AIAA, FSEMC, WATS) -industry white papers to feed back key findings to the stakeholders. -inputs to the International Committee for FSTD Qualification (ICFQ) The steering group met on 23 July, and is planning the following actions: 1. Circulate the Master Plan document and invite participation in the Working Group 2. Issue Constitution and Terms of Reference, and obtain FSG approval 3. Establish the Working Group on the basis of responses to the invitation 4. Request the Working Group at its initial meeting to: a. Review its objectives b. Identify Work Packages, leaders and assistant leaders. See Appendix 1 for possible Work Packages. c. Define meeting targets d. Agree outputs and timetable e. Set methodology for future meetings and discussions f. Set up a reporting procedure to the Steering Group - GY |
JD-EE
Vaguely, I should do a bit more homework to brush up on the basics. "Tumble" is the physical analogue (from old gyroscopes) I am trying to use to describe the function becoming unreliable, based perhaps on accelerometers going wrong, but I won't comment further as I think the laser ring gyro has been adapted due in part to its higher reliability. (Fault tolerance). As to lost calibration, causes of that would, it seem, remain in the electrical, rather than physical motion, domain. Do I understand that correctly? I'll stop with the wandering off into partial panel wilderness. Sorry, BOAC, for bringing that up again. In the process, I've learned a bit, so maybe not a total loss. Where I think I wandered off was in pondering an ADIRU fault consideration. We have tended to discuss that more on the Air Data side (based on pitot tube / probe issues), rather than IR faults (Inertial Reference) within that system, based on the ACARS messages. FDR will doubtless be much clearer regarding what was doing which. That said, there have been (in a general sense) ADIRU faults in the past the pilots had to trouble shoot due to impact on their attitude reference display. The summary I just reviewed again shows crews to had sort them out or handle them via (IIRC a 777 incident) by degrading Auto Pilot funcitons ... perhaps while being in a bit more benign flight environment than T Storm penetration? Thanks to OK465 for the sim training and unusual attitudes points. Appreciated. :cool: |
Lemurian;
You must have an A330 FCOM. Have a look at 1.27.30 and tell us exactly what you understand about pitch control in ALT1 or ALT2, especially the use of speed in these laws. I never mentionned lateral control |
HN39;
Thanks for the added precision. Does that prevent the pilot from flying "the airplane according to aerodynamics and piloting experience"? |
Originally Posted by Lemur
Don't know what you're talking about.
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Flight Control Laws
Gentlemen,
if I may, I intend to shed some more light on this touchy matter of Flight Control Laws on the accident type. Each Flight Control Primary Computer will perform its own computations, and decide its own Flight Law, based on available data. FCPCs (or PRIMs) manage Normal and Alternate laws, while FCSCs (or SECs) manage Direct law. The Master PRIM (normally PRIM1) then decides which Law gets used for the whole system. Lemurian wrote : the whole system reverted back to the pilots with an ALT2 FC law 02:11:55 EFCS1 X2,EFCS2X,,,,,,,FCPC2 (2CE2) / WRG:ADIRU1 BUS ADR1-2 TO FCPC2, HARD This is definitely a wiring fault, where FCPC2 and ADR1 lose their connection. Lemurian, could you be so kind as to demonstrate with certainty that FCPC2 reached indeed a state where it operated in Alternate 2 law ? I am not so sure. Normal law would be the preferred mode even with only two ADRs, as long as they produce similar values. FCPC1 certainly did operate in ALTN2, as correctly demonstrated by BEA in its intermediate reports. It was Master PRIM until it failed along with its SEC1 partner : 02:13:45 F/CTL PRIM1 FAULT 02:13:51 F/CTL SEC1 FAULT Then FCPC2 became Master of both elevator halves and THS. |
DJ77,
I never mentionned lateral control But of course, just mentioning the pitch control allows you to criticize in a very sleazy manner this architecture. So, when you wrote ... / ALT LAW 2 / Pitch control Identical to ALT 1 law" Note the ambiguity: nothing is said if Alt law 2 is due ADR faults or disagree conditions. you very conveniently forgot to mention that the conditions for ALT2 are, among others :DOUBLE ADR FAULT ...ADR DISAGREE... Thank you, the doubt I had is lifted. |
Originally Posted by Svarin
Each Flight Control Primary Computer will perform its own computations, and decide its own Flight Law, based on available data. FCPCs (or PRIMs) manage Normal and Alternate laws, while FCSCs (or SECs) manage Direct law. The Master PRIM (normally PRIM1) then decides which Law gets used for the whole system.
Originally Posted by Svarin
This is unfortunately not accurate enough in our case. I urge you to reconsider the very particular case of FCPC n°2, after it lost connectivity with ADR1 following this failure :
02:11:55 EFCS1 X2,EFCS2X,,,,,,,FCPC2 (2CE2) / WRG:ADIRU1 BUS ADR1-2 TO FCPC2, HARD This is definitely a wiring fault, where FCPC2 and ADR1 lose their connection.
Originally Posted by Svarin
Lemurian, could you be so kind as to demonstrate with certainty that FCPC2 reached indeed a state where it operated in Alternate 2 law ? I am not so sure. Normal law would be the preferred mode even with only two ADRs, as long as they produce similar values.
Originally Posted by Svarin
FCPC1 certainly did operate in ALTN2, as correctly demonstrated by BEA in its intermediate reports. It was Master PRIM until it failed along with its SEC1 partner :
02:13:45 F/CTL PRIM1 FAULT 02:13:51 F/CTL SEC1 FAULT |
PJ2 However, in two Flight Crew Training Manuals examined, fuel transfer is mentioned. It is stated that the handling characteristics of FBW aircraft are independent of the CG in Normal and Alternate Laws and it is not necessary to command a FWD fuel transfer in the event of heavy turbulence in cruise. why AB means that FBW did not longer need more stability in turbulence ??? what has changed between 1988 and 1997 ??? neither the basic aerodynamic of the sky nor the basic concept of the wing (profile) is quite different between an A300-600R and an A330-200 (both with trim tank) |
Ref deSitter's #1812 - Despite technical b/g my basic SLF status causes me to enter this discussion among a large group of wise and honorable (and sometimes agitated) elephants with considerable trepidation, but would it not be useful for the Flight Control Computer to show some sweat? It knows - or can be taught - how close it is to turning the job back to mankind.
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In reading the pilots of this type, I understand AB to require autoflight in turbulence. Likewise, the lack of need to rearrange the fuel components when anticipating flight into turbulence. This last requirement, that Fuel is allowed in the Trim Tank in Turbulence, applies to ALTLAW 1 and ALTLAW2, but what about DIRECTLAW? With an aftward cg, do control movements that are handled by the autoflight present a challenge to pilots in DIRECT that they are not used to reacting to? In the AB manual, for instance, references are made to cruise. What is the AB direction if not in cruise, or manual flight of any description, for that matter?
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Would someone be kind enough to reply with a general summary of where the investigation stands now? I tried reading back through the threads but it seems to ah...change direction quite often or something.
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THS Trim Tanks. CVRs & "Hot" Microphones.
Hi grity,
Just a reminder that the A300-600 series are of similar vintage to the A310. (They retain the A300 wing, if memory serves, unlike the super-critical A310 wing.) They have conventional flight controls, and (presumably) a traditional-size THS. Tubby Linton will be able to explain more about the MAC figures involved. However, speaking generally about swept-wing, medium-to-long-range jet transports – those without trim tanks – the following may help. When pushing range towards the limit, the centre tank has a substantial amount of fuel at take-off. (You only put fuel in it if all the wing tanks are already full.) Because the centre-section is forward of the optimum CG, the aircraft is nose-heavy and inefficient until the centre tank is empty. So during the first few hours, the THS is in an inefficiently nose-up-trim position (i.e., having to generate more negative lift than later on). Having the THS trim tank full does not necessarily create an abnormally aft CG, but it can if the designers want it to. EDIT (May 20) The point I was trying to make above is that the A300-600R (and A310-300) trim tanks are unlikely to be used to create "relaxed stability": merely to offset the normal forward-CG problem that I have illustrated. The A330/A340 are a different case, because of FBW. This is not to suggest, however, that they would be unflyable in Direct Law at cruising altitude. Current certification criteria would not permit such a regime, if my understanding is correct. Garage Years, Take the point about NR headsets, which I used from the early 1990s. Being short-haul, we had our headsets on nearly all the time. What I can tell you is that, when the cabin crew entered the cockpit, we had little difficulty hearing them and conversing. Admittedly, we often slid one earpiece off, but I'm not sure that was necessary. My understanding and experience was that it was steady "noise" that was almost eliminated: e.g., the 400Hz hum from the AC electrics, the airframe noise, and the engine noise. I'd be surprised if "hot mikes" (for CVR recordings) were phased out on UK-registered aircraft as a result of noise-reduction headsets. Do we know if Air France CVRs use them? |
Svarin, thanks for your inputs. I was thinking that the ADR1 / FCPC2 wiring failure could have been just a transient. I find it is unclear how exactly pitch control works in ALT1 / ALT2. Whilst these reconfiguration laws can be triggered by 2 or 3 unreliable airspeed sources the FCOM says it uses speed. I offered that the FCPCs may use a “default” speed value or default gains in case of missing (or unreliable) airspeed data. Good enough for me.
My point is: an FCPC in charge of pitch control in a load factor demand law, which is the case in both ALT laws, apparently have to establish, one way or another, reasonable gain values. Now what happens if in a particular sequence of events, especially when the ADR data may be restored randomly and asynchronously relative to the computer’s sampling rate, this FCPC is led to use (perhaps momentarily) an erroneous speed value and then determine wrong gains? Is the airplane always flyable in such a case? Of course I have no doubt that all the software was carefully studied and checked in all possible ways but !!!!! happens. I agree this may be far-fetched and stand ready to be guillotined. |
Irrelevance
All this discussion of what the Airbus FMCs do is interesting, but irrelevant - when humans are confronted by a computer that is either not working, or working in a regime they are not intimately familiar with, they freeze - they go into brain lock. This happens with all kinds of systems, from text editors to banking systems, and I'm sure it happens with aircraft FMCs. If you are going to design airplanes that fly on the edge of control with the help of computers to constantly trim them, then you'd better make sure that the airplane still manually flies like an airplane at the drop of a hat, one that a pilot can control *instinctively*, despite his brain lock! This is a criticism neither of pilots, nor of computer systems - it's the truth of human/computer interaction. It will never matter how well designed are Airbus' or Boeing's FMCs - if they are not purposely designed to make the airplane act like an airplane under pilot input, then they are not only wrong-headed, they are dangerous!
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plasmech,
The BEA is continuing to do a read-out of the two recorders. There have been no disclosures of the content of the CVR, yet. The BEA has said that based on the initial read of the FDR, that no major hardware or software problems were found, but that as the data is further analyzed, anomalies or problems requiring corrective action or steps may be identified. The two bodies recovered in their seats have been flown to Paris, and the examining laboratory has announced that the bodies can be identified using DNA. The Ile de Sein is headed back to the site of the plane; it had been in Dakar for a crew change. Quite likely it off-loaded in Dakar those parts of the plane, e.g., engine, cockpit seats, that had been retrieved, and these are probably being flown back to France. It is not clear what parts of the plane will be retrieved, possibly cowlings if these were not retrieved in the initial recovery of parts. I believe two judges in Paris will now determine whether any more bodies will be retrieved. |
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