stall indicator
 

I'm having a problem keeping up with the volume of posts, but I don't expect anyone has suggested this:
Hang glider pilots often tie a ribbon to the down-tube.
Maybe something that could be seen from the cockpit, but slightly more robust than a ribbon could work?

Can't speak for Dozy, but two relevant arguments that come to mind are Schipol and Bournemouth. The 737 autotrim does drop out with a/p - and the consequences when pilots didn't immediately realise weren't pretty (although at Schipol it was probably a minor contributor with not watching the thrust the major one).

The common thread to me is not that A control laws are better than B, or visa versa, but that pilots should be properly trained to fly the a/c they are flying, including stall recognition and recovery. It appears that this has been lacking across the industry for a while, hopefully now in the process of being fixed.

Bill,
Something "slightly more robust" already exists. It's known as an AoA vane (sensor). There are a couple of those fitted to the nose.
Your ribbon is no more a 'stall indicator' than the AoA vane (or indicator), unless you know the stall angle of attack....
And there is no indication so far that the AoA sensors had any problems (unlike Perpignan).

But what about number 1 stuck at 2.1 deg ?

Ones complement and sign-magnitude both do this.

Not sure how much either is still in use though - not a lot, most things are twos complement, but maybe in some niches.

I have a very vague (and probably wrong) recollection that fixed-point datatypes in Coral66 and maybe ADA (not used that much) might have used ones-complement magnitude under the hood. On some hardware. Coral was definitely used in aviation (maybe still is, I haven't worked with it since the 80s) as is ADA.

Missed that, you got a link?

Hi Christiaan,
Yes, Confiture is right.
See for example longitudinal axis simulation graphs p.44, incidence notes on detailed flight parameters p.30-33 (French report), as well as other graphs.

Below, "incidence IRS1 [DA] (FDR)" is showing a value for alpha probe #1 which remains blocked at 2.1° until after 0210:50; later, it follows other probes but its output is under-reading.

http://takata1940.free.fr/longitudinal.jpg

Smilin-Ed
Only one question: In a FBW Airbus how will you as pilot sense which way to trim?

Explain why Trim needed when trying to recover, Loss of Control? Autotrim is like the co-pilot moving the wheel, but in secret? No bicycle bell, or Clacking?

takata,
Merci pour le lien.
I admit I missed that.
Not sure from where the FDR takes the "incidence IRS1 [DA] (FDR)" signal (I somehow doubt it's the 'raw' AoA vane signal), but I agree it further complicates the issue.....

Perhaps.
Perhaps it points towards the amount of ice on the airframe??
Perhaps not.

Autotrim, THS. "hand flying"
 

Many previous planes had "beeps" or other indications that the autopilot or the "autotrim" ( hate that word) was moving the HS. In fact, an infamous crash near Indianapolis caused by LOC and ice building on the HS has a "whoof" sound on the CVR indicating that "otto" was trimming. When the crew disconnected the AP, shazam! Other big time problems with that incident, for another thread.

The huge HS can easily override the relatively small movements of the actual elevators. Just think about the area and remember the real "law" about rho vee squared times Cl times surface area. Then there's ol' mach. So near the critical mach, the elevators at the rear of the HS can become ineffective, hence the "all moving" stab on all fighters and some commercial planes since 1950.

The problem we dinosaurs have with some FBW implementations ain't the fact that electrical signals go to the actuators versus cables, pushrods, or hydraulic lines. Pure hydraulic pressure controlled from the stick/yoke valves that have been around for 60 years. The problem is that the engineers and maybe some pilots added "features", "protections", etc. that get in the way of hand flying when various components so to lala land. No commercial plane I know of is certified if it's basic aerodynamics are not up to spec.

Because we dinosaurs are used to trimming the pressures off of the stick/wheel/yoke, we expect things to remain relatively calm after a bump in the air or completely letting go of the controls. And if we were using otto, we expected some indication that otto had trimmed the plane versus us. So any reversion from automated flight to manual flight should not require instantaneous analysis of what the hell is going on.

I repeat for the nth time........ You can build and implement a FBW airplane that flies exactly like those of yore. Replace the tubes, cables, etc. with electrical wires and no big deal. It's only when many "features" and "protections" are added that you have problems with the training and competence of the crew. I only flew one state-of-the-art high performance jet that had a decent artificial feel to the stick, and it was a bellows doofer connected to the stick thru a pneumatic line that made it harder to pull/push when the airspeed went up. So the idea of force feedback to the FBW stick would be nice, but not completely necessary. In fact, it would be veeeeery nice as long as we had an indication other than our seat-of-pants that it was inop.

The basic rules are still applicable when a lotta electronics and such go away - pitch and power for last known condition, then go as gently as possible from there.

But Ice Detectors 1+2 didn't detect any (P110 EN)

... but also problems with sensors and probes and everything that has to process their readings ...

In the meantime, when everything is by the book, it is Fantastic !


Question is why BEA 'missed' it too ... ?

Look at the graphs cyan curves I posted above: graph 6 "Position PHR" = THS setting, and graph 7 "Position gouverne de profondeur gauche" = Left Elevator setting. Now, compare them.

As expected, THS is not following short term g-load elevator demands. During the whole sequence, 0209:40 - 0210:54, THS setting is changing from -2.8° to -3.4° (negative = NU)... hence a maximum variation of less than 0.6° in 1.14 minute. During this whole sequence, the long term pitch demand increased from about 3° NU to 11°NU, with up and down in between.

Stall warnings, sounded at 0210:51 and stall followed 10 seconds later. From this point, the large NU demand was confirmed both in amplitude and in duration by elevator ncrease up to Max NU deflection, and they were mostly maintained here during the following minute. Consequently, THS followed its order by moving in the very same way up to Max NU deflection.

There is absolutely no mystery about that: OTTO had NOT trimmed the plane versus pilot demand !!
- OTTO only did what it was asked to do!
Of course, this end result, with hindsight, is contrary to the good setting for a rapid recovery action... but nobody really wanted to recover from this situation at the first place!

If this pilot is pulling, He has help from this THS. So he must take the timing of his pull, rmember how long, and hold down the same amount when he wants the nose to go lower? This pilot has not remembered some things, how will he know what to push? Is pushing also harder than pulling now, it gets less nose move?

You say loudly the trim is because of the pilot, but not the other? The pilot is not doing what he is to do? He does not know this trim, even if he remembers the airplane actions from gthe training? The THS knows, why not tell the pilot also?

What, you say noone wants the recovery? Also that the airplane in this shape is too slow for r4ecovery? What is this?

Sorry, I'll have to pull out the doc... artificial feel was not "my" system. But yes, I agree, I would think "q" was definitely one of the inputs.

I can't remember any UAS incidents ever being mentioned.

Concorde went above Mach 1 at about FL350. At cruise altitude (FL500 to FL600) and Mach 2, TAT was in the order of +120°C, so icing was not really a problem then. And yes, at that altitude, Concorde was basically 'above' the weather, including the ITCZ..

AP disconnect and autotrim
 

You are correct, TK.

And seems to me that the 'bus AP disconnect is very benign.

The problem we dinosaurs have is we still see things like "overspeed/mach" inputs and such versus simply letting the crew fly a fairly good aero design with appropriate warnings that they are going too fast, or getting too slow, or exceeding some AoA values, and so forth.

CONF has brought up a good point. My discourse on the FBW design concepts was to illustrate that we don't need an awful lot of sensors to fly a plane with a good, basic aero design. After all, we're not talking the F-22 or Eurofighter or Viper. Basic aero laws will provide static and lateral stability. But if we fool with "Mother Nature" by flying with an aft c.g., we can get into trouble. For the AF447 incident, looks like c.g. was not as far aft as would be normal for that phase of flight, so I rule out a serious static stability problem due to the c.g. One of the only reasons we didn't have a "direct" law in the Viper was the thing was intentionally designed and flown with negative static stability until above 0.9 mach or so. During the flyoff with the YF-17, the performance difference was dramatic. You can still see the difference when the Blues perform, or a Super Bug does a demo flight. That critter is very comfortable at extreme AoA because it is a conventional design. End of war story.

That AoA #1 reading...
 

{New here - Hi to all :)}

That initially "stuck" reading (according to the FDR) from AoA sensor #1 is interesting, isn't it. Presumably its output got voted out of being used, due to the discrepancy with the other two sensors, but the fact that it was different doesn't seem to be explained in the BEA report.

Understood, but that lack of report from the detectors, doesn't prove ice wasn't present ("absence of evidence" and all that...), especially since there seems to be evidence of ice in that CVR noise noted by the BEA (page 73 English version).

What else could be the cause? Could the lack of report from the ice detectors be due to a different type of ice being present, than they were designed / able to detect? Being only a GA pilot, I have no idea how the ice detectors on an A330 work - any pointers?

After the logged AoA sensor #1 value gets "unstuck" from the 2.1deg value (thanks takata for that), at around 02:10:52, note that its value then gets "stuck" again for a while, but this time at a much higher value (> 40 deg) at around 02:11:45, when the other two AoA sensor values dip below 40 deg (page 107 English version).

My overall view is that there is a general "stickiness" to that sensor, and that's telling us something - whether it's affected by ice (of a type / amount / location not picked up by the ice sensors), or is a faulty sensor (lack of effective heating?), or ... ?

As I said, I hope the AoA #1 output wasn't being used due to earlier discrepancies, but I haven't seen that confirmed anywhere (I'd be very happy to be corrected on that!).

Has it been confirmed what AoA sensors were fitted?

Pretty likely the Thales C16291AA given the choice of Pitot tube, if so one could have been suffering an extreme variation of the known fault at low temperature:-

EASA Airworthiness Directive

Note that the use of 3 sensors means that a single failure can be accommodated - but surely there should eventually be an ACARS maintenance warning to get the probe looked at?

There was a direct relationship between the rolling and pitching moments and that is best illustrated by superimposing the rolling data over that of pitching. Also remember that at all times the yaw damper continued to work and the rudder was being deflected up to the maximum of +/-7.9° allowed by the RTLU. Worth checking is the Normal Acceleration [g] to which has been added a smoothed line (red), and observe the 'g' recorded during the period of the THS movement.

The graphic below is a rejigged composite of those presented by the BEA, with the exception that the topmost section shows CAS as calculated from BEA data by HazelNuts39.
http://oi51.tinypic.com/3097cs2.jpg
The sections covered by a pale yellow background are related to the period in which the THS moved from 3°NU to 13.6°NU, and the sections with a pale green background draw attention to the effect of a reduction in thrust.

During periods of prolonged right rolling/banking, the nose dropped in unison and the heading changed.

If the situation had been understood by no later than 2:12:10, there was a very good chance that the ND bank then taking place could have been converted into sufficient airspeed to allow a coordinated recovery. It didn't happen, as continued NU inputs and application of TOGA thrust saw to that.

@mm43 & HN39:
 

Good observation!:ok:

Thx for the effort to make this clear.

@Diagnostic & sensor_validation:

so AOA#1 could be effected, however didn't had any influence.

FCPC using median AOA (or outvoted AOA#1), AoAsw using highest AOA value.

Thales AoA sensor EASA ED
 

@sensor_validation (re post#6628318)

Very interesting AD, thanks for the link! I haven't seen any mention of the specific fitted AoA sensors, but that AD would certainly explain AoA "stickiness" wouldn't it.

It's a relatively recent AD (originally issued Jan 2010), but they are not limiting the list of potentially affected Thales p/n with any specific manufacturing date range - so perhaps that AD could apply to the AoA #1 sensor on AF447, if those Thales AoA sensors were fitted.

(IMHO it also goes to show that any AoA display should display the measured values for all 3 sensors, to allow the crew to take a decision abut which are most believable, in case of discrepancies - it must not display a single computed mean / median, as that calculation could be wrong, as the AD points out.)

@A33Zab - Many thanks for confirming that this erroneous AoA #1 value wouldn't have been used by the FCPC. We seem to be lucky that only 1 (and not 2) AoA sensors were producing erroneous values here - otherwise there's obviously a potential risk of another Perpignan-type situation, where the one "correct" AoA value gets voted out :uhoh:

Case closed
 

Smilin_Ed said


This is just conclusive. There is nothing else to argue about. I don't know why the apologists for automation cannot simply admit that they are wrong, or at least to admit defeat and claim that they are right anyway, as a face-saving maneuver.

great diagram mm43.

The thing that really gets to me about the graphic is the intensity of the initial zoom climb and the associated g forces....you cant really call that an appropriate hand flying response to autopilot drop out and speed indication failure by any conception..

I just wonder if the poor sod simply freaked out at all the alarms...tragic if the warnings of irrelevant failures ( irrelevant that is to the important task of of maintaining constant pitch and attitude) ended precipitating a bigger failure.

I suppose you could have some nice relaxing ladies voice saying " pitot failure...then a softly spoken expletive....its your aircraft now..we cant help you anymore...maintain constant attitude and thrust...please check the auto trim etc etc..."
to keep the poor man calm (if Any bright spark wants to automate the emergency response )

Hi mm3,

Thanks for the graphic. I'm confused why the stab trim does not move significantly (up to your yellow band) - whilst the CAS has dropped from 275 to about 225 kts. I would have thought the auto stab trim would have followed the real reduction in airspeed. I realise it appears that PF seems to have pulled 1.4g then reduced to 0.5g during this period.

Does the delta g prevent the movement of the stab trim during those manoeuvres?

Airbus pitch trim
 

I get the idea that many real pilots here (I am not one) do not understand the Airbus pitch trim. As far as I can see it's not in any sense Trim as we know it Jim.

As I understand it:-

With autopilot off and hands-off the stick in Normal and Alternate Laws the aircraft maintains constant g (hence absent other inputs - pitch attitude). As I understand it the crew of AF447 (and indeed any AB not in direct law) could have wound the pitch trim wheel as much as they liked and as long as the elevator did not run out of travel no aircraft pitch changes would have occured. The computer would have matched the manual THS movements with elevator movements to exactly compensate so that aircraft g (pitch) was maintained.

The Airbus auto-trim merely seeks to keep an adequate range of elevator authority available (zero degrees of elevator deflection?) - however with a long time constant (delay if you like) so that it does not try to follow every little twitch of the stick/elevator. In Normal and Alternate Laws it has *no* influence on aircraft pitch while there remains elevator movement in the required direction.

So:- the THS and auto trim had NO BEARING AT ALL on this incident. Nil, null, zip, nada.

I will allow that perhaps when in the deep stall at extreme AoA (60 deg was it?), certain THS/elevator combinations may have been advantageous but that is strictly in Chuck Yeager territory and in any case no serious attempt was made to get the nose down so artful trim twiddling was never going to be considered by this or probably any other crew.

Of course all is not sunshine and roses. In direct law the pilot must ensure that the THS is positioned manually so as to allow adequate pitch authority. The exact same issue however occurs on Boeings too and Boeings too have crashed as a result. Airbus knockers can just therefore put their toys back in the pram forthwith:-) The issue of extreme THS "trim" and subsequent lack of needed pitch authority in rare circumstances appears to me to be an industry wide problem. It can occur in Boeings on autopilot disconnection and in AB on reversion to Direct Law. The burden of being in an unusual attitude and needing to use manual trim to get adequate pitch authority to recover is surely pushing at the boundaries of The Average Airline Pilot?

Thanks jimjim1 for that lucid explanation.

So even in ALT2 Law, it would have been useless to hold the stab trim stationary by hand - since the computers would simply displace the elevators to a new "null position" and "trim the new attitude". Longitudinal speed stability is still not returned, hence no feed back of feeling slow and hence heavy in pitch

@DozzyWannabe.
I wish I was as good as you. You make it sound so easy. Please see:
http://www.pprune.org/tech-log/376433-af447-132.html post 2632.

Posted by jimjim1Exactly, at last someone has noticed the absolute irrelevence of much that has been posted about this accident, particularly concerns about autotrim and alleged skittishness of 'manual' control at high altitude. All these would be appropriate to a conventional aircraft controlled in a conventional way, but the Airbuses after the A320 are NOT conventional in their control systems, and as jimjim says the sidestick commands g. And it is a confessed non-pilot who has to point this out. One minor quibble is only true if the AT is maintaining speed correctly, if the thrust is insufficient for the drag, the speed will reduce and the controls will maintain g by increasing pitch attitude until... stall, which is what happened here. You can argue whether this is a good way to control the aircraft, but the first duty of anyone flying one is to understand this crucial point. Clearly the AF447 crew, and many others posting here, don't.

Hi deSitter,
A very long time ago, this case was closed for any people able to understand how autotrim works and that manual trim is available, at any time, if one doesn't like what autotrim is doing. One, which is able to understand it, obviously doesn't need to save his face either.

AF447 case is all about pilot's imputs which are not coherent with the situation, not about an automatism which stupidly followed orders given; it is like asking that the elevators should not follow nose up orders when stall warnings were sounding. In fact, it is a case calling for more automation as some would have liked that this aircraft could be able to determine all by itself that pilot's orders were stupid and should not be followed by any aircraft stupid control surfaces.

Hi rudderrudderrat,
Sorry but it doesn't make sense. How would the computer "simply displace the elevators to a new "null position" and "trim the new attitude" without changing the THS setting? When trim is activated manually, autotrim is frozen, can't displace anything anymore. If one is trimming manually, he's overiding autotrimming and computers would resynchronise with manual imputs after this point.

Hi takata,
I can't find any reference to that - it would appear to be in error.

In the same way the system copes if the stab is "frozen" in a position with the loss of the relevant hydraulic systems.
Similarly I'm saying that if the stab trim is held stationary, it makes little difference to Normal or ALT LAW in pitch, because the elevators will be repositioned to compensate - until they run out of authority.

edit.
The design of Pitch stable Law without Alpha Max protection, on an aircraft which is inherently naturally speed stable (by design concept), during UAS is not logical. Why would you want to do that?

Hi jimjim1,
It is not correct. THS do not replace elevators control and elevators are not used to replace THS trim.
Consequently, any large change of pitch is not compensated by THS change and longitudinal stability is maintained. Moreover, in alternate law, C* law gain is reduced, hence 1g is not maintained "at all cost", and certainly not when the sidestick is moved back and forth.

See yourself:

Angle of attack data processing algorithms
 

According to the ATSB interim accident report on QF72, the FCPC treats AoA differently from the other parameters (which was an important factor in the QF72 occurrence):

Hi takata,
Did you mean for the rest of the flight?

I interpreted the line "in case of manual action on the hand wheel," meaning only whilst the hand holds the trim wheel.

How does the system cope with stab frozen then, either due to relevant double hydraulic loss, or if the stab trim wheel is held stationary by hand?

Manual trim overrides autotrim (micro-switches disconnect the auto-drive if I remember correctly) for the duration of manual input... hold the trim wheel or move it and that prevents autotrim - the computers monitor the trim state during manual trim and on manual 'release', the computer reacquires control from where the manual inputs left off.

So let's assume PF realizes he has inadvertently driven the trim to +13NU due to his excessive NU elevator demands - all he has to do is twiddle the trim wheel ND to something he likes (let's say +3NU) and let go. The trim will remain at or about +3NU unless he starts waving the SS in a nose up position for a long enough to cause the lagged THS autotrim to decide that the PF really wants more NU. To be honest it doesn't seem at all evil or that hard to understand, so long as you are half-aware of the systems of your aircraft - you know the one you are qualified to fly.

Doesn't speed stable also mean pitch stable? When I studied aerodynamics a hundred years ago, the instructor said all conventional airplanes are unstable in pitch. Their sphugoid may be long in period, but still there. Nobody challenged him.

From what I read, the A330 was not designed to be pitch/speed stable, but pitch/speed neutral.

It seems nice the way you tell things, but now if you have a look at the Airbus documentation, where is the quote, where is the "BE AWARE" that in some cases you would be better use MANUAL TRIM despite the fact AUTOTRIM is active or at least operative ?

In other words, which simulator exercice has ever encouraged such way of thinking ... ?

To be simple, this aircraft is not meant to be hands fly. To keep some stabilities, a pilot must be known to fly with gentle move. No offense to this Airbus, hand fly is a definition to Pilot. To know this aitcraft is to know in his Law, the rolling is by direct to controls. This why the aircraft is worming through the air, sometines great, but always for the Pilkot mto be anxiuous, because he is causoing these rolls.

Trim is not an emergency to control for recover stall. It is to reduce drag, and too much small moving the elevators. It is slow for rewasons as above, the elevators are the prefer mechanism.

These Blue Angels fly their plane close to the ground, loudly, and slowly, with the mush,. it is as ballet.

But when these planes go 'depaert' in the altitude, the pilots must let go for the RBW to get flying back normal? Recover by wire. Red face rfor pilots who let go. Wht not some help automatic for these pilots of the 447.

Who wants trim to be silent, large, and possible to kill in this Stall. Automatic trim. This is for nonsense. See if you like, this pilot was not gentle. He was not confident, but he was stubborn. These make a pilot the choice not to be flying, but others. Where is this Captain?

Self confidence is good, but not bravado. For rolling, possible this right wing is trimmed down, for some reason, but pilot can control, but he plays back and forth, instead of holding some gentle trim? This trace for roll is too accurate to be some weather, too. consistent.

For Mr. takata Does this THS not start moving UP during the first Pitching UP by pilot? This because he is accedlerating above 1.2 g and the THS inhibits in this region? Would it have started to move soonerr, if he was more gentle in the pitch? Thank you sir.

3holelover re my comment about the plane image control surfaces clue, "Airbus will also display that on the ECAM FLT CTL page. (but you all knew that, right?... Is the suggestion for a separate screen always displaying this?"

Yup. It's there when you need it. Otherwise ignore it. If it also included an arrow to show AoA that would kill two birds on one separate display that is ignored most of the time. "Mousing" through a list of display menus when in the situation the plane fell into is not feasible - even if it is one push button beside the FD display.

I think a new picture is nice. But, for who? For you? The answer is not in new. Old is the secret for this survival. Old pilot named Captain. Too much lights, too many colors, no one understands, and Captain is gone. More lights and pretty pictures....that is the tickets?