One reason the A310 finally made it was banking to the left at top of climb.
Is roll command on A330 in ALTN2 the same as in NORMAL law (roll rate command)? Thx |
If you haven't already done so, take a look at this post by sadpole in the other thread. Some insight into what the Human Factors Group probably missed.
|
Originally Posted by Lyman
(Post 7291055)
Dozy regarding my fishing.... It is Airbus who warns not to reselect Autopilot: "The autopilot may command undesirable Pitch attitudes, resulting in damage to the aircraft" (or something like that.) It is not I who first asked re: the autopilot in AL. If as you say reselect is impossible, why do Airbus warn pilots not to "reselect"? For that matter, why do they direct the pilot to turn off a/p as part of the drill? Isn't it already off, and "latched out"? Hmmm?
I think / recall that the a/p-off latch depends on precisely which law the a/c gets into. That depends on how many ADRs fail and for how long and maybe in which order. That in turn depends on which pitots ice up, how badly, and maybe in which order - which will vary. I recall that there has been at least one case where a/p was re-engaged soon after UAS and did the wrong thing due to speeds being in agreement but still erroneous. The line in the procedure looks like it is to ensure that ap/fd are off (they might have dropped out but maybe not). I think there has been additional guidance (that's come up on these threads) about not re-engaging them too quickly (ensure speed info is back to normal first). |
Hi,
Interesting EASA publication: http://ad.easa.europa.eu/blob/easa_a...AD_2010-0271_1 So .. in 2010 .. they put emphasis on the FD ... (after the AF447 case) |
henra, #259
Is there a voting system between ADR and IR ? I understood there is a voting system between the ADR's and a voting system between the IR's. And that logic was described. But between the two? How would you vote between Air Data and Inertial Data? Normally they are complementary (not competing) data. sources to improve overall performance is not new. For example, GPS / inertial mixing has been in use for some time. A brief description may help to illustrate why this is a good idea, with of course apologies for those who know all this already. An ins system (IRU in airbus speak) works by dead reckoning and is subject to drift over time. By dead reckoning, I mean calculated from the point of origin, or start position. The accumulated position error could be as much as several nautical miles per hour, though current state of the art may be much better than this. GPS doesn't work by dead reckoning, but by direct measurement of absolute position and has far greater accuracy, to within a few feet over much of the earths surface. However gps can suffer from signal dropout and loss of accuracy in some regions and is susceptable to jamming. With the gps / inertial mixing scheme, some very smart software augments the ins data with that of the gps to provide better long term accuracy, redundancy and improved error detection. For example, if the margin between the ins and gps data exceeds a given threshold for a number of samples, one or other can be tagged as a degraded source, while still providing good data over the short term. That is, we now have a holdover capability in the event of a temporary fault from either source. By now, you can probably see where i'm taking this in terms of a baro / inertial mixing scheme. Ins data could be used to augment and cross check air data information. From what i've read, the current systems are independent and any results of cross checking between the ins and air data speeds (baro) are not presented to the flight deck. The problem of using ins data to correlate air speed is that the ins measures ground speed. However, at any given point in time, there is a historical timeline and ongoing relationship between the two. This could be used in the short term to provide an indication of air speed in the event of a temporary pitot tube failure. If one assumes that the wind speed remains fairly constant short term, such a baro inertial mixing scheme could be a valid solution to the loss of air speed data, upon which so many other subsystems depend. There other ways to measure air speed, such as the airbus developed laser measuring system and which is, iirc, available as an option on the A380. Hopefully, it will become mandatory at some stage. Feel free to hack at all this if you like :-)... |
Originally Posted by jcj
Interesting EASA publication:
http://ad.easa.europa.eu/blob/easa_a...AD_2010-0271_1 So .. in 2010 .. they put emphasis on the FD ... (after the AF447 case) |
I see repeated reference all over PPRuNe to this being the 'correct action'. Was this in fact so, i.e.a QRH item before 447? http://www.bea.aero/docspa/2009/f-cp...90601e2.en.pdf |
Originally Posted by infrequentflyer789
(Post 7291514)
I recall that there has been at least one case where a/p was re-engaged soon after UAS and did the wrong thing due to speeds being in agreement but still erroneous.
Because of the digital nature of the equipment, the AP switch is not a type where AP status can be determined by switch position - AP status is determined by the presence of the Autopilot button light on the FCU and the PFD status instead.
Originally Posted by BOAC
(Post 7291769)
- I see repeated reference all over PPrune to this being the 'correct action'. Was this in fact so, i.e.a QRH item before 447?
|
If you haven't already done so, take a look at this post by sadpole in the other thread. Some insight into what the Human Factors Group probably missed. Probably won't happen unless the regulators wake up. Too many sacred cows.:} |
BOAC, jcjeant, Dozy & Infrequentflyer789,
I am thinking that perhaps (maybe) the AD 2010-2071 resulted from the TAM incident (perhaps others?). In the TAM incident the NTSB investigated and noted: On May 21, 2009, at 2147 eastern daylight time (EDT), an Airbus A330-233, Brazilian registration PT-MVB, manufacturer serial number 238, operated by TAM Airlines as flight 8091 from Miami International Airport, Florida, to Sao Paulo Guarulhos International Airport, Sao Paulo, Brazil, experienced a loss of primary speed and altitude information while in cruise flight at FL370 over international waters, south of Haiti. About 6 seconds after the autopilot disengaged, recorded data indicated two brief re-engagements of the autopilot. Concurrent with the re-engagement, a pitch up to about 7 degrees nose up and slight climb was recorded, and the pilot reported a stall warning. Left side stick pitch inputs were recorded about one second after the autopilot disengaged from the second brief engagement, as the airplane climbed to about 38,000 feet. The autopilot remained disengaged during the remainder of the event, and the crew turned about 60 degrees to the left to diverge from the weather area, and the altitude decreased to about 36,500 feet, before reversing and increasing again. About 3 minutes and 30 seconds after the initial airspeed drop, the No.1 ADR returned to 260 knots, and the 300 foot altitude discontinuity ceased, indicating an altitude of about 37,400 feet. Left nose down stick inputs and a decrease in pitch were concurrent with the altitude returning to 37,000 (FL370). Then autopilot and autothrust were then re-engaged and the flight continued to Sao Paulo in alternate law with no further incident, no injuries, and no damage. Post flight maintenance checks on the airspeed system revealed no discrepancies. Just a thought.... |
@TD - Good catch. I think it was recognised as a general industry-wide issue before then though - I'm thinking in particular of the Flash Airlines 737 where the Captain repeatedly called for re-engagement of autopilot as he unwittingly manually took it outside of the envelope.
FWIW, while some of what sadpole said is true, some of the prejudice he showed in that post really rubbed me up the wrong way. |
Flash Airlines 737 |
Originally Posted by BOAC
(Post 7292073)
- is really in another arena. What I am trying to establish is whether the UAS QRH action PROMULGATED BY AF at the time of 447 was as described.
http://www.bea.aero/docspa/2009/f-cp...nexe.06.en.pdf There was some debate over the "safe conduct" clause preceding it, but nevertheless, the first two memory items are AP/FD and A/THR to "OFF". |
AoA and FMGEC:
@HN39:
Accuracy of the vane sensor = +/- 0.3° at 100kts. --- About the FMGEC voting logics: The FMGEC uses different logic to compare the inputparameters. The logics used are by voting, passivating or two by two comparision and/or a combination of those. For the airspeed (considered as slow changing parameter) the two by two comparision is made on the (ADR) monitoring side of all 3 sources (ADR OWN, O3 and ADR OPP-osite), the result of this is passivated to the command side which only receives parameters of ADR OWN and ADR #3. (the command parameters are following the selection of the ADR source selector however will revert to the good source if the selected source is considered not to be good, as it was in AF447 between 02:10:46 and ~02:11:07. Already said before it is rather complicated, one parameter may pass the logic while an other parameter could 'reject' the ADR as being unreliable. The two by two comparision example: http://i474.photobucket.com/albums/r...9/TwobyTwo.jpg |
Thanks, DW - my French was not up to the other link! I think it is fair to say, however, that the AD is much clearer in both layout and explanation. As you say, the 'Safe conduct' bit could well have caused problems, in particular if the 447 crew did not, for some reason, feel it was relevant, and they never got to the 'level off' bit where the FD OFF was heavily emphasised..
|
Originally Posted by syseng68k
(Post 7291662)
If one assumes that the wind speed remains fairly constant
short term, such a baro inertial mixing scheme could be a valid solution to the loss of air speed data, upon which so many other subsystems depend. In short, I think your scheme still has the common mode failure that the 3 redundant pitots have - the same external conditions may mess up the pitots and your inertial backup. Additionally, you've now added another failure mode - if the pitot airspeeds vary wildly (but accurately) due to rapid air mass changes, is your inertial mixing going to vote out the correct data ? |
Do not forget that for three years on, the topic has been discussed ad nauseum; in that focus is lost the emergent conditions 447 experienced 2:10:04.6 instant. Safe conduct of the flight is the underlying parameter of any pilot; they do not need to begin differentiating and splitting hairs
the instant Speeds are lost. That is the emergency, and I defy any one here to state they would be available instantly to gauge coldly if the flight became endangered with the unexpected loss of a/p. Assume one of sadpole's aces were flying? Does he coolly hold steady, to assess, knowing the flight is not in jeopardy? He does nothing with the stick as the airplane bounces and descends, rolls? Or does he make inputs to correct? The airplane was left maneuvering at a/p drop, and the initial corrections applied were correct. So the correct action has placed the handling pilot in harm's way: He is handling, and the response is not being assessed correctly by the ASI, his one true ally has quit. His reactions to the first eleven seconds are in the record, and it is these inputs that set the stage for disaster. the accident was born in these first eleven seconds, the cart had been upset. There is no going back, the crew was committed, by virtue of the unexpected change in instrumentation. With PNF's remonstrations to "go back down", we see the possibility for salvation. The PF rejected this verbiage, his instruments had just revolted, does he trust the second in command? Or does he buy time by placating him, and continuing his incorrect path? We know the answer. The materials used to date the manuals must be examined closely, some of the dates and alterations are in disagreement, and some were "updated" without notation. I would direct anyone's attention also to a photograph in the final report, showing "Arm 36G" in the Rudder. It is completely different from the one supplied by BEA initially, the one that began the discussion of the Arm attachment discrepancies in the image with the text of their analysis. Closely inspect this photograph, please. Dozy, are you sure the Stick shaker/pusher has been abandoned in favor of FBW? 50's technology? The 330 cannot fly with the best Stall Warn available? The Warn that trumps even the speed/AoA aural that was dismissed/ignore by the crew? And the finest Stall recovery tool, the Pusher? Are you saying that Airbus will improve the aural qualities of its SW, and that will be sufficient? So again, would 447 have benefitted from the Shaker/Pusher? I say yes, and I would question your position that she would not have possibly even entered the Stall with this equipment? I would admit that furnishing the Shaker to a side stick might be problematic, and the Pusher to an electronic controls system as well. |
@BOAC
This is pure speculation, but sadly it seems just as likely that the startle response was so complete that any thoughts of procedure never even got a look-in. By saying this, I am absolutely not denigrating the unfortunate crew - as I said in the other thread, even the best have bad days.
Originally Posted by Lyman
(Post 7292241)
...I defy any one here to state they would be available instantly to gauge coldly if the flight became endangered with the unexpected loss of a/p.
and the initial corrections applied were correct. Dozy, are you sure the Stick shaker/pusher has been abandoned in favor of FBW? 50's technology? The 330 cannot fly with the best Stall Warn available? The Warn that trumps even the speed/AoA aural that was dismissed/ignore by the crew? And the finest Stall recovery tool, the Pusher? Are you saying that Airbus will improve the aural qualities of its SW, and that will be sufficient. The stick pusher is not the "finest" anything - it was a product of its time. If you read HTBJ you'll find anecdotes from DP Davies about how many contemporary line pilots hated the thing and didn't trust it. Whether that enmity was justified or not, the fact is that stick pushers were only ever compulsory on G-registered aircraft of a certain vintage. It can be argued that the pusher was really only necessary on T-tail aircraft, as the conventional empennage layout is not susceptible to the "deep stall" condition - and in fact aeronautical engineers design airframes to develop a nose-down tendency at the stall without requiring control input. The A330 is no exception - in this case the natural tendency was defeated by the PF who held the primary flight controls in a nose-up position for the majority of the sequence. Modern aircraft with yoke controls retain the shaker (which can be - and has been - ignored with fatal results), but the pusher has moved into history across the industry. The FBW designs from both major manufacturers, rather than providing automatic stall recovery, instead try to prevent the aircraft from approaching stall in the first place, whether via hard protections in the case of Airbus, or by increasing opposing yoke force in the case of Boeing - and as I said above, the aircraft are designed to naturally nose-down at the stall. Sadly, no amount of design can prevent human interaction from defeating the failsafes. |
Accuracy of the vane sensor = +/- 0.3 at 100kts. Let's assume that the accuracy varies as the inverse of dynamic pressure, then it would be +/- 0.8 at 60 kts, and +/- 3.3 at 30 kts. Perhaps the stall warning computer could take those tolerances into account? It may also be possible with the data from wind tunnel tests and AF447 to expand the airspeed indicating PEC (pressure error correction) table to higher AoA's, to reduce the IAS error at high AoA. |
Sadly, no amount of design can prevent human interaction from defeating the failsafes. The idea of combining > 1 independent, limited reliability sources to improve overall performance is not new. There other ways to measure air speed, such as the airbus developed laser measuring system. With the current design, the 3 pitot tubes are not only of the same type and same manufacturer, but they are also located pretty much in the same place - under the nose... To me there are many lessons to be learnt. Perhaps in the event of unreliable airspeed the AoA indication should become more prominent. Perhaps the stall warner inhibition should only be below a certain radio altitude. Perhaps, perhaps, perhaps. There are perhaps 100s of improvements that can be made, but each one must be considered and the impact on all phases of flight and all types of operation must be analysed before implementing them. I can't subscribe to the idea that the current design is somehow "incomprehensible" or "technically flawed" it is fairly standard from what I see, and follows well established principles. We shouldn't look at one small sub-set of operation and criticise it in isolation, or try to correct it without considering the effect on the whole system. In my opinion, the overall system failed catastrophically because of poor interaction and breakdown of communication between the aircraft and the pilot, the causes need to be established and corrected without introducing more dangerous failure modes. |
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