AF 447 Thread No. 10
Thread part -
(a) #1 starts here and finishes here. Posts = 3895 (b) #2 starts here and finishes here. Posts = 2537 (c) #3 starts here and finishes here. Posts = 2073 (d) #4 starts here and finishes here. Posts = 1070 (e) #5 starts here and finishes here. Posts = 1980 (f) #6 starts here and finishes here. Posts = 1696 (g) #7 starts here and finishes here. Posts = 1355 (h) #8 starts here and finishes here. Posts = 1552 (i) #9 starts here and finishes here. Posts = 1476 Total posts to date = 17634 .. with in excess of 2.7 million views overall. Links to the various BEA reports are given below. If I have missed any of the useful papers, please PM me with the URL and I can include it. (a) BEA site - French, English - Report link page - French, English (b) Interim Report (No, 1) Jul 2, 2009 - English (c) Interim Report No. 2 Dec 17, 2009 - English - Update Dec 17, 2009 - French, English (d) Estimating the wreckage location Jun 30, 2010 (e) Wreckage search analysis Jan 20, 2011 (f) Briefing and associated update May 27, 2011 - Briefing - update French - Briefing - update English - Briefing - update German - Briefing - update Portugese (g) Interim Report No. 3 July 2011 - French, English (h) Links to final report Jul 5, 2012 and associated documents. Miscellaneous pertinent links - (a) Airbus Operations Golden Rules (b) ALPA FBW Primer (c) C* and Civil Transports - Cranfield (d) Longitudinal Flight Control Design - RAeS (e) Longitudinal Stability: Effect of High Altitude and CG - Boeing (f) pitot static system performance - USN (Pax River) FTM (g) The Problem of Automation: Inappropriate Feedback and Interaction, Not Over-Automation. Donald A. Norman UCSD (h) Upset Recovery - 16MB zip file (i) Ironies of Automation. Lisanne Bainbridge UCL (j) Cognitive Capability of Humans. Christopher Wickens Uni Illinois (k) Trust in Automation: Designing for Appropriate Reliance John D. Lee, Katrina A. See; Human Factors, Vol. 46, 2004 (l) Training for New Technology. John Bent - Cathay Neil Krey's CRM site Search hint: You can search PPRuNe threads with a filter in Google by using the following search string example - ths af447 site:http://www.pprune.org/tech-log/ This will search for mentions of THS in the AF447 threads of tech log only. Just change the THS in the string to whatever you want to look for. This allows one to search for any term or phrase of interest throughout the threads. Adding the site:URL end part is the magic that restricts Google to only searching in Tech Log. This filter technique is absolutely wonderful and can be used generically to find things of interest in PPRuNe - appears to work OK in the PPRuNe search function as well. In respect of Google searching, JenCluse has added some suggestions - a) indenting the text block with a (one) Tab, *and* b) emphasizing the fact that it is a search text block with some manner of . . . <SearchText>, or "SearchText", or |
Originally Posted by Lyman
Has it at any time been attempted to hold the trim wheel to prevent Autotrim? Have line pilots ever done this? In addition to quick sticking to prevent the THS from Trimming? Could something have gotten stuck in one of the wheels? Was anyone sitting or resting a foot on the pedestal? In NO sense, does Airbus manual trim resemble manual trim in any other civilian jet of my experience. (various models of Lear, B737-engineering sim, DC9) It is highly unlikely that anything could jam/interfere with the manual trim wheels. Only the top quarter of the wheel is available and it's tightly "cowled". |
Originally Posted by TTex600
In the narrowbodies, I've attempted manual trim as per the FCOM' statement that manual trim is available and primary at all times. The manual lies. Auto trim fights the man trim wheel and removes any pilot applied man trim as soon as the pilot releases the wheel. When forced, the trim wheel will make jerk-y pitch movements.
Of course, if the flight control system is off in La La land, you still can seize control, but it will be at the expense of someones free hand and (apparently) smooth control. If you do this, you are fully responsible for observing all aircraft limits, so I can understand a bit of caution in applying this technique, but ultimately you do have the "hammer" should you want to use it. The crew of AF447 could have stopped the trim from its run to the nose up trim limits if they had been aware of the motion. Just as there isn't any good reason to point the nose high in the air at cruise altitude, there is also no good reason to have full nose up trim dialed in at cruise altitudes. |
Disturbing post
Good grief, Tex.
Your war story scares the hell outta me. For some reason, I expect that when the human "commands" something, that the machine will obey. Sheesh, I can see HAL learning how to read lips in order to counter the clever humans. |
Machinbird;
The BEA Final Report into the XL Airways A320 accident at Perpignan makes for interesting reading, bearing in mind what information has been provided thus far on the THS design, stall warnings, normal, alternate and direct laws and so on. (The G-THOF incident has been brought up here before). We know that the THS is the long term follow-up to elevator input and so with AF447 and here the trim dutifully followed the sidestick commands as the stall exercise at Perpignan was approached. Some here have offered the notion that the THS should stop trimming at some point but what are the all the effects of such a design change? Should it be stopped at a stall indication? In these two accidents that would have been too late as the THS was already at the NU stop. Ironically, for AF447, stopping the autotrim function at that point would remove the ability of the autotrim to follow a ND stick order and reduce from -13.6 back to normal as the trim did in our little sim exercise, as it would have for AF447. However, for the XL A320 dropped from normal to alternate and then quickly to direct law where manual trim was required but by that time things were happening too fast. There's an animation on the BEA site, (with a caution not to use it to come to specific conclusions...a caution for ALL animations!) TTex600, re the autotrim and THS, you told only part of the story! http://images.ibsrv.net/ibsrv/res/sr...cons/icon7.gif The trim went back to its original setting when you fiddled with it because that's what it is and does...it's a full-time autotrim in normal and alternate laws. Manual (mechanical) trim IS available at all times just as the FCOM says, when needed, (such as in direct law or a G+Y Hyd flr), it will stay in the position the pilot puts it in. That's just part of knowing one's airplane. Hey gums...no worries. From the BEA Report, p.92-93: 2.4 Functioning of the Automated Systems When the real angle of attack increased, the blockage of AOA sensors 1 and 2 at similar values caused the rejection of the ADR 3 anemometric values, even though these were valid. This rejection was performed by vote without any check that the parameters were consistent with each other. The crew was not aware of this rejection, except indirectly through the loss of CAT 3 DUAL approach capacity. The low values of the limit speeds did not attract the crew’s attention. Due to the blockage of the AOA sensors, calculation of the limit speeds was erroneous and the triggering of the AOA protections in normal law was rendered impossible. The values of the speeds corresponding to angle of attack protections (Vaprot and Vamax) were proportional to the computed airspeed of the aeroplane (see 1.16.2). The display of the amber CHECK GW message on the MCDU(58), a consequence of the gap between weights calculated on the one hand by the FAC, based on the angle of attack, and on the other hand by the FMS, based on the takeoff weight and the fuel consumption, would have allowed this anomaly to be detected. This message is however associated with no aural warning, which contributes to reducing its importance. On approach to stall and taking into account the dynamic of the flight and of the complexity of the displays, the automatic changes in the control laws can fail to be perceived and their consequences can sometimes be misunderstood by pilots. In this case, the passage to direct law rendered the auto-trim function inoperative. Even if the amber USE MAN PITCH TRIM flag was displayed on the two PFD artificial horizons, the crew did not notice the position of the stabilizer and did not command the trim wheel manually during the twentyfive seconds in direct law between 15 h 45 min 15 s and 15 h 45 min 40 s. From this time on and for the rest off the flight, as a result of passing into abnormal attitudes law, the amber USE MAN PITCH TRIM flag was no longer displayed. The systems thus functioned in a degraded manner, without the real overall situation of the aeroplane being known by the crew. The necessity to trim the aeroplane manually can occur in a situation that is already degraded, as was the case during the accident. This then leaves the crew no time to analyze the situation, especially since, on this type of aeroplane, the crew was used to not performing this task in normal operations. One of the only circumstances in which a pilot can be confronted with the manual utilisation of the trim wheel is during simulator training. However, in this case, the exercises generally start in stabilized situations. It should also be noted that the technique for approach to stall does not remind crews of the possible need to have recourse to the trim wheel in direct law. This absence de reference to the use of the trim is also mentioned in AAIB report into a serious incident to a Boeing 737 on 23 September 2007(59). In addition, the angle of attack constitutes essential information to characterize the situation of an aeroplane on approach to stall, while the speed information is that which is always used. (59) http://www.aaib. gov.uk/publications/ bulletins/june_2009/ summary___ aar_3_2009___ boeing_737_3q8__g_ thof.cfm |
Originally Posted by PJ2
Some here have offered the notion that the THS should stop trimming at some point but what are the all the effects of such a design change? Should it be stopped at a stall indication? In these two accidents that would have been too late as the THS was already at the NU stop.
EDIT:: In AF447 the THS was at about 3.1 degrees NU at stall warning 2. The effect of limiting the THS to that value is described here. |
Originally Posted by PJ2
(Post 7370551)
Some here have offered the notion that the THS should stop trimming at some point but what are the all the effects of such a design change? Should it be stopped at a stall indication? In these two accidents that would have been too late as the THS was already at the NU stop. Ironically, for AF447, stopping the autotrim function at that point would remove the ability of the autotrim to follow a ND stick order and reduce from -13.6 back to normal as the trim did in our little sim exercise, as it would have for AF447.
I agree for Perpignan's A320, but not for AF447: In the latter case, the trim was -3° when the stall warning went on, and the motion toward -13° was done with the stall warning shouting all the long. Still, as stated previously, I'm no more advocating that inhibiting the NU autotrim when S/W in ON would be such a good idea: 1/ Someone quoted the "black swan" theory, and that's worth to think about (plus the fact that under the current implementation, the elevators may try to compensate for the "unavailability" of the autotrim). 2/ As you said, that would be of no use at all in a Perpignan-like scenario. KISS principle. If autotrim available ("normal" scenario, the crew must be aware of that, and of how it works). If autotrim not available, the crew must be notified of that (USE MAN PITCH TRIM must be displayed, which was not always the case in the system logic, IIRC that has to be (has been?) corrected). |
Originally Posted by PJ2
TTex600, re the autotrim and THS, you told only part of the story! The trim went back to its original setting when you fiddled with it because that's what it is and does...it's a full-time autotrim in normal and alternate laws. Manual (mechanical) trim IS available at all times just as the FCOM says, when needed, (such as in direct law or a G+Y Hyd flr), it will stay in the position the pilot puts it in. That's just part of knowing one's airplane.
As usual, my round-a-bout point is that the bus doesn't fly like "any other airplane". I have attempted to "fly it like any other airplane"' and it DONT. Some have a seeming desire to discus this accident as if the Bus is flown like the airplane they retired from, or like an airplane that is pilot flown vs computer flown; some want to assume that Bus trim works from their perspective. This just isn't so. One needs to place one's self in Bonin/Roberts exact shoes before judgement. Edit to add: the bus almost totally removes trim from the pilots conscience thought process. More later |
...autotrim to follow a ND stick order and reduce from -13.6 back to normal as the trim did in our little sim exercise, as it would have for AF447. ...but in today's "self study" world such language should be more clear Whatever happened to chalk.....or for that matter, experts? |
Originally Posted by TTex600
(Post 7370310)
Auto trim fights the man trim wheel and removes any pilot applied man trim as soon as the pilot releases the wheel. When forced, the trim wheel will make jerk-y pitch movements.
In NO sense, does Airbus manual trim resemble manual trim in any other civilian jet of my experience. (various models of Lear, B737-engineering sim, DC9)
Originally Posted by TTex600
(Post 7371150)
As usual, my round-a-bout point is that the bus doesn't fly like "any other airplane". I have attempted to "fly it like any other airplane"' and it DONT.
The trim arrangement is not the same - by design - but the average layman is unlikely to know what trim does, and so that's usually put aside. The FBW Airbus pilot is not required to have trim as part of their conscious thought process, and the fact that autotrim has barely warranted discussion up until now implies that in almost all cases, that's not a problem because the system is very reliable. In this particular design, manual trim has gone the way of wing-warping, trim tabs and cable reversion - in that other ways to implement that function have been found that either reduce pilot workload or design complexity. A pilot that does not have to trim manually is no less a pilot for not having to do so, and just because older types required manual trim to be part of the pilots' muscle memory does not mean that it should always be so. The fundamental fact is that the trim worked the way it did because the PF's pitch commands required it to. Maybe it's worth revisiting that behaviour, maybe it isn't - but to make a blanket design change that would involve significant man hours in development, fitting and re-training on the basis of one relatively minor factor in one accident - a factor that was a consequence of crew action - would be foolish. |
Hey Tex. Autotrim won't "fight" the manual trim wheel, but you will probably feel the electro-mechanical interlocks disengage when you hold it for the first time. |
If I understand the design, it'll disengage as soon as it feels any resistance - so it won't try to move the wheel against the direction it's being moved in or against the position at which it's being held. In that sense it's checking to see if it can re-engage, but it won't actively counter (i.e. "fight") what the pilot is doing with it.
|
...so it won't try to move the wheel against the direction it's being moved in or against the position at which it's being held. |
Originally Posted by DW
one relatively minor factor in one accident
DW, in this 10. thread you work as designed. Two different conceptions of effective aircrafts :suspect: |
@roulishollandais:
The systems status of AF447 and Perpignan was different, so I'm treating them as unrelated until strong evidence suggests otherwise. The "Effective Aircraft" theory seems to be yours alone, and I must confess I don't follow it, but that's possibly because I'm a poor reader. |
1. "Effective aircraft"
Originally Posted by Dozy Wannabe
The "Effective Aircraft" theory seems to be yours alone, and I must confess I don't follow it, but that's possibly because I'm a poor reader
isbn=0309056888...National Research Council (U.S.). Committee on the Effects of Aircraft-Pilot Coupling on Flight Safety - 1997 - Transportation - 208 pages Implications for Design of the Effective Aircraft Dynamics Reduce time lags in the high-frequency effective aircraft dynamics. To reduce tendencies for ... In this book (1997), some very good Machinbird reference, you will find 51 occurences of "effective aircraft". [/quote] I already posted this reference months ago... :) I would have been very proud to have the idea of that perfect concept ! 2.
Originally Posted by Dozy Wannabe
one relatively minor factor in one accident
One crash is not less serious than ten, if working better in system conception would help to decrease that number, and we refuse to do it. Research and development is mandatory.:rolleyes: |
OK - so looking at that document, I notice two things.
The FBW Airbii seem to be no more susceptible to PIO/APC than any other type based on the amount of time they've been around and no discrepancy has shown itself, and the fact that there is no significant positive discrepancy in accidents between FBW Airbii and other types suggests that Airbus's "effective aircraft" design is no more or less flawed than any other modern type. |
Semantics: The theory seems to be about "Effective Aircraft Dynamics", i.e. the dynamics of aircraft, effectively, or the effective dynamics of aircraft (and pilot).
|
HN39, re
Originally Posted by post #6 [URL
http://www.pprune.org/tech-log/493472-af-447-thread-no-10-a.html#post7370832]I[/URL] agree that inhibiting autotrim would not be a good idea. But how about limiting the range of THS settings it trims to as suggested in my post here? That would retain autotrim for trimming nose-down in response to sidestick demand, just as it does in normal law above alpha-prot. EDIT:: InAF447 the THS was at about 3.1 degrees NU at stall warning 2. The effect of limiting the THS to that value is described here.
As the discussion had turned to autotrim, elevator and their behaviours I was curious to see if the Perpignan accident which was an intentional reduction of speed to test low-speed flight and the alpha response, offered any new understanding. As expected the THS moved to trim NU as the stick was held back and speed reduced. The flight data shows that the THS reached the NU limit at the same time that the stall warning occurred, (I still don't know if a stall warning stops the autotrim on the A320 or not. I suspect not). Accordingto the BEA Report, stick inputs at the initial stall were insufficient to cause the THS setting to move ND. The aircraft reacted to the developing stall and rolled, with sideslip causing a disparity between the airspeeds ADRs 1 & 2. This caused the FAC then ELAC to reject all three ADRs and the flight control laws reverted to direct law, requiring manual input to the THS which was annunciated on the two PFDs. This is a case in which the THS would not have moved towards the NU position with forward stick if autotrim were stopped with the stall warning. The case may be "academic" in some eyes due to the fact that there was no time for forward stick but it serves as a sufficient counter-example to indicate that the idea needs careful thought. If Bonin had placed the stick full-forward and held it, we know that there was a likely chance for recovery. But there is a great deal behind any such pilot's decision to take such action. So AZR I agree with you regarding not stopping the autotrim at a stall warning and I'm merely adding here something to the recent discussions on THS and elevator behaviours which I think hasn't been considered, (unless I've missed someone else's comment on this). I agree with you HN39 regarding limiting the autotrim in some form. My thought is, as the Perpignan accident serves to illustrate, at what point and for what reason should the autotrim be stopped in its motion (either way), and then re-engaged again? It IS re-engaged in one circumstance: The abnormal attitudes law, in which autotrim is stopped but re-engaged once the abnormal attitude limits are no longer exceeded and the aircraft is recovered, (AMM). TTex600; Re One needs to place one's self in Bonin/Roberts exact shoes before judgement. This is a performance accident. There is nothing about the airplane that caused an absence of SOPs, CRM, a disciplined cockpit and a disagreement between crew members which went unaddressed and unresolved, (PM taking control, PF taking it back after PM says get the nose down, etc). This absence has been noted by the BEA and much earlier by many here including me. That isn't judging the crew, that is asking why, when SOPs, CRM etc are what we do, they didn't respond as expected of an airline transport crew. Training, checking, standards, a professional culture are intended to ensure the performance of these fundamental and critical tasks but here that did not occur. Why? Startle effect has been noted for many years now. No one is immune of course, but the difference in the character of response is what solid training, knowledge, memory items and disciplined CRM is about. For lack of a better word, a "fear" has crept into the checking and standards regimes partly due to risks of liability but also through other, more subtle reasons, that prevents some required bluntness and otherwise clear address regarding crew performances. I would never return to some of the means I've seen to "ensure" crews do their job but the cockpit isn't a democracy, either. If the airplane let them down, even in part and after they were well into serious trouble, then we need to ask the question, would another random crew similarly be "let down"? If so, how, when and why? |
Startle effect ?
I think these pilots indeed had enough reasons to be suffering from startle effect However, the result was different from that of AF447 Why? The answer is not difficult to find United Airlines Flight 232 - Wikipedia, the free encyclopedia So ... fail to prepare .... prepare to fail |
Originally Posted by PJ2
The flight data shows that the THS reached the NU limit at the same time that the stall warning occurred, ...
|
Originally Posted by HN39
OK465:
Thank you for your post #1392. I understand most of what you are saying, except when you say "a more relaxed SS input". A valid experiment would compare the two cases at exactly the same entry conditions and exactly the same pilot inputs. On 'theoretical grounds' I remain convinced that the resulting airplane trajectories would be identical up to the point where the elevator reaches the stop. What you're talking about here is maintaining the Nz law but on the elevators alone, without the trim participation. Such behavior would be in total contradiction with the logical Airbus philosophy where as soon as the THS stops moving automatically, whatever the circumstance, flare, alpha prot range, direct law, the pilot needs to apply a constant deflection on the stick in order to obtain and maintain a desired attitude (as long as he do not manually trim). To maintain the Nz law on the elevators alone would be totally illogical IMO. It would be also like masking the reality to the operator. At this point what is needed is Direct law, why anyhting else ? People around like to think about more automation, or OTOH to not change anything to the present logic, in reaction to AF447, when the most logical path would be to simply switch to less automation as soon as unreliable data are detected by the system. If the system had that humility to further switch to Direct law when the UAS was detected, AF447 was an all different game with a probable landing in CDG. |
Originally Posted by CONF iture
(Post 7372824)
when the most logical path would be to simply switch to less automation as soon as unreliable data are detected by the system.
If the system had that humility |
Originally Posted by CONF iture
If the system had that humility to further switch to Direct law when the UAS was detected, AF447 was an all different game with a probable landing in CDG.
|
Just as Autotrim acts over longer term than Stick input (elevators), is there a relationship between the pilots' knowledge of this and an attempt to maneuver without its help? It seems there may be a conscious effort to avoid changing the AoI of the aircraft by using quick inputs, followed by opposites?
Has anyone explained this rapid use of the SS? Does it relate to a 'workaround' of the trim? It is especially odd considering the altitude, and airspeed, to see large and rapid stick displacement. Any Bus pilot care to address? |
CONF iture;
You're an A330 pilot, (captain?) and know and understand the requirement to use and adhere to SOPs and to employ standard CRM communications and problem-solving techniques. The unilateral actions by the PF, within a second of the start of the UAS event do not conform to standard responses to abnormalities, nor did the actions of the PM as the problem rapidly degraded. HN39 states that a reversion to direct law would not have made a difference in this case. I agree. What should have been a straighforward response to an abnormal event instead took the aircraft rapidly out of stabilized cruise flight and beyond the boundaries of controlled flight. It is no surprise that what the airplane presented them with while well beyond test-pilot territory confused them because they acted outside of expected and trained responses. This kind of response is not specific to the A330, or a Boeing design or a Douglas etc and so making changes to a design only covers this one specific response; where will the next "abnormal" come from which again challenges a crew who may exhibit a similar response? These are issues to consider and not dismiss in favour of a singular focus on a specific type of aircraft or flight control system. |
PJ, this leaves open to question, in my mind, just what it is in the Air France simulator periods that one must demonstrate or practice in order to comply with the sim period requirements.
A hard question to ask the chief pilot at AF: What tasks and problems am I to stress or require in the limited simulator time for my __ X number __ of pilots and how shall I implement that to get the best training value for the money spent? I am not sure how the investigation will go, insofar as any legal proceeding vis a vis Air France, but I'd be very, very interested in seeing the answer to What does the AF training and currency program look like? What is done versus what is on paper? That's a small piece of the puzzle, as it would address far more than UAS issues. |
PJ2
You say... "The unilateral actions by the PF, within a second of the start of the UAS event do not conform to standard responses to abnormalities, nor did the actions of the PM as the problem rapidly degraded." Not exactly, and that is the first time I have seen a statement of that sort relative to the differences in Flight Law relating to manual flight. You go on to urge the commingling of a/c types other than Airbus A330 when addressing standards of high altitude assumption of manual flight. I cannot agree. PF took control, and announced it, his inputs were consistent with handling required, and no one will ever know if he sussed ALTLAW2b. Since the outcome of this event resulted in the deaths of 228 souls, I think it is critical that the initial induction of LOC is understood specific to this type. Respect, |
Probably a Red Herring (?)
I checked the forums but didn't find a thread about this. Fifty incidents involving total cockpit power loss in A320-series planes. I didn't feel comfortable starting a new thread, so I post this here. Be aware that this is a two-page article:
Airbuses suffer cockpit power failure, await fixes - seattlepi.com Obviously, not a word about whether this problem occurs in 330/340 flight decks. :eek: |
That's 50 incidents in 23 years. I wouldn't be surprised if similar issues had cropped up on the widebodies (despite the physical implementation being completely different). But I'm convinced that such a failure did not play a part in AF447 because throughout the sequence on the CVR, all the crew are maknig reference to attitudes, altitudes and ECAM messages which would not be visible if a panel failure had occurred.
|
Lyman,
PF took control, and announced it, his inputs were consistent with handling required |
Originally Posted by Turbine D
(Post 7373226)
Can you explain how this statement is true?
[* - and that's "trolling" in the classic "fishing" sense - a deliberately incorrect statement, fashioned to attract replies - as opposed to the more recent definition, meaning outright inflammatory statements against a person or group.] |
Garbage. Upon loss of Autopilot, PF took controls, and announced it. He then input in two axes, both needing handling, and both correct in direction.
From then on, things went South, But don't you dare try to envelop his initial actions into three years of spin... Troll? That is a stretch.... For three years on, people have been spinning the accident into ever fanciful and flimsy conclusions of PE, whilst defending and lauding the airframe as perfection personified..... Hamster wheel under construction, and with odious helpings of wannabe "pilots" waxing scholarly on things that will never be known. You take the freaking cake. Presumption piled on assumption... |
Originally Posted by Lyman
(Post 7373279)
He then input in two axes, both needing handling, and both correct in direction.
For three years on, people have been spinning the accident into ever fanciful and flimsy conclusions of PE, whilst defending and lauding the airframe as perfection personified..... |
I agree with PJ2 about his analysis of the crew reactions and our discussions about control law reversion, as well as the function of the THS.
The thing that bothers me is the lack of "feel" that the system provides to the pilot. I fully understand the Nz law, which seems to me primary for the 'bus, and corrected for pitch attitude with little regard for AoA. That's important - corrected for attitude. So you don't really have a one gee command if not fairly close to zero pitch attitude. Hence, HAL is trying to achieve 0.87 gee at a 30 degree pitch attitude, and less if you figure the sine/cosine/etc . The big deal with the THS is that it is trying to relieve the required stick pressure/displacement if the pilot is holding a command other than the one gee corrected for pitch attitude. For a commercial airliner, this makes perfect sense to this dinosaur. The problem is that simply releasing pressure/displacement does not give you the "feel" that we used to have when the basic aero of the jet tried to achieve a trimmed AoA. In other words, going too fast or pulling too hard, the jet would try to go back to the trimmed AoA/gee if we relaxed the pressure/displacement ( NOTE: Our primitive FBW implementation used pressure , not stick displacement, so simply relaxing pressure would command the jet to go back to the trimmed gee). . So the THS concept seems to get in the way of what we old farts "felt" when we were commanding something that the jet was not trimmed for. Does this make sense? The Boeing FBW implementation appears to use a mechanical "artificial feel" that requires ever-increasing pressure/movement to maintain other than trimmed gee/AoA. I don't see this on the 'bus. My opinion after these last three years of discussion and analysis of the 'bus flight control laws leads me to this : - The jet performed exactly as designed. - The THS logic and lack of increasing stick pressure to command an unusual pitch attitude/AoA "helped" to maintain a condition that made a recovery very difficult for the average or even above average pilot that had not thought this scenario through. The 'bus has postitive longitudinal stability thoughout it's envelope unless the fuel trim system is completely FUBAR. So the jet would appear to act as we old folks would expect in the so-called "direct law". Unfortunately, the system keeps trying to achieve a gee-command ( corrected for pitch attitude) and there's no obvious indication/feeling via the stick that the plane wants to achieve an AoA versus a gee. - The AoA inputs to the flight control logic should be emphasized more IMHO, and good AoA sensors work well down to 50 or 60 knots of actual dynamic pressure, regardless of what the pitot-static system(s) is telling the system. - Crew coordination and a clear "chain of command" is essential if you are flying a "crewed" airplane that allows more than one pilot to have a control input. My only experience in "crewed" planes was as an instructor in a family model of two jets ( ultimate authority!) or in the VooDoo, which had a radar operator in the back seat with no flight control inputs. So I defer to those here who have thousands of hours dealing with the "CRM" issue. All I ever had to do was ask, "Gums? What the hell are you doing?" |
Originally Posted by DozyWannabe
Two more statements of (at best) dubious provenance, intended to elicit a response. I'm not biting this time - I wonder what will hapen if people stop biting altogether?
|
Then maybe the spectre of a thread 11 - in which we all go over the same ground, discussing nothing new - would be banished.
I for one am more than comfortable with that. EDIT:
Originally Posted by gums
(Post 7373362)
The Boeing FBW implementation appears to use a mechanical "artificial feel" that requires ever-increasing pressure/movement to maintain other than trimmed gee/AoA. I don't see this on the 'bus.
|
Hi gums,
I agree with PJ2 as well, there doesn't appear to be any reason to believe there was anything wrong with the aircraft. Regarding the Viper that you flew, is there any change to the latest F-16 models as to handling and "feel" via the sidestick? Is sidestick pressure rather than displacement still used? |
Originally Posted by MachinBird
Not really a surprising result. In Normal and Alternate 1&2 Laws, holding the trim wheel can result in inadequate control effectiveness for proper operation of the flight control system.
Of course, if the flight control system is off in La La land, you still can seize control, but it will be at the expense of someones free hand and (apparently) smooth control. If you do this, you are fully responsible for observing all aircraft limits, so I can understand a bit of caution in applying this technique, but ultimately you do have the "hammer" should you want to use it. The crew of AF447 could have stopped the trim from its run to the nose up trim limits if they had been aware of the motion. Just as there isn't any good reason to point the nose high in the air at cruise altitude, there is also no good reason to have full nose up trim dialed in at cruise altitudes. Can you confirm that the AF447 crew could have held the trim wheel and stopped the trim from its run to nose up limits? In my experience in a 320, I was able to eventually force a small pitch "bobble" when moving the trim wheel to the limit of the available "one hand grip" travel. The wheel feels like it's attached to a bungie cord and with a hundred fifty souls behind me, I had no intention of going anywhere further with trim than that initial "one handful movement". Can anyone confirm what would happen if a pilot, on a test flight of course, just held the trim wheel? Why weren't they aware of the continuous trim motion? Why no "trim in motion" claxon, or other indication? The system can warn of a jammed stab, but not a run away stab. Oh I know, it wasn't run away, it was just doing as it was told. And a find job it did. |
Originally Posted by TTex600
(Post 7373457)
Can you confirm that the AF447 crew could have held the trim wheel and stopped the trim from its run to nose up limits?
... Can anyone confirm what would happen if a pilot, on a test flight of course, just held the trim wheel?
Originally Posted by A33Zab, thread 4, post 327
"An override mechanism, which is installed in the PTA (Pitch Trim Actuator),
makes sure that the mechanical control through the trim wheels cancels the electrical control. When a manual command is made with the trim wheels, the override mechanism gives priority over the electrical command from the FCPCs. It mechanically disconnects the PTAoutput from the mechanical input(via electro-magnetic clutch) and also operates the overriding detection switches which in turn signal the FCPC's to stop any electrical command from the FCPC's." Why weren't they aware of the continuous trim motion? Why no "trim in motion" claxon, or other indication? |
All times are GMT. The time now is 09:11. |
Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.