DozyWannabe

Everyone wants the truth*, but in some cases the best that can be managed is an informed supposition.

In this case, the Captain's order to level the wings followed by reference to the horizons is neither followed by a comment to the effect of "but we have no horizons" from the crew, nor does the Captain say that the horizons are out. We know that the altimeter was working from the callouts and we know that it's likely that attitude indications were displayed too ("you're going up so go down"). The idea that the flight deck displays went entirely dark is not supported by the evidence we have.

Not at all - we have an earlier instance of his speech pattern where he refers to things sequentially : "There I don’t know there it’s going down". If he'd been implying that either or both the PFDs were unreliable then he'd likely have mentioned the ISIS ADI only. Instead he says "the horizon the standby horizon". I ask again - if any of the ADIs weren't working, why did he or either of the F/Os not say so?

CVR reading can be a very subjective game, which is why the people that do it tend to specialise in that area to the exclusion of all else. Picking the AF447 CVR apart is relative child's play compared to a case like TE901, in which two very different readings have split opinion on the accident for decades, or Palm 90 - where the NTSB's specialist spent literally months trying to determine whether the response to the Engine Anti-Ice call-out was "On" or "Off" (eventually it was determined to be "Off").

[* - EDIT : not only including me, but *especially* me. Given that 99.9(rec)% of all the flying I'll ever do is as SLF it is not in my interest to defend a problematic or dangerous design on the part of any manufacturer. This is one of the reasons I get extremely vexed when I'm accused of "defending" Airbus.

But at the same time I have no truck whatsoever with the propagation of misinformation and falsehood for the sake of political point-scoring, and the fact is that the amount of hot air I've seen talked about Airbus over the years would be enough, were it to be harnessed and pumped into the fuselage, to put every airframe they ever made into the stratosphere in perpetuity.]

bubbers44

I guess if you stalled and were in a 40 + degree nose attitude down when the captain got there he would have a hard time trying to figure out where the blue sky was on the attitude indicator. It wasn't visible. The attitude indicator is made for competent pilots not these guys.

gums

I am becoming increasingly disturbed by some of the assertions here regarding the longitudinal static stability characteristics of the 'bus.

From every document I can find, I see that the jet has a decent positive static stability characteristic. In short, the jet wants to achieve a trimmed AoA except for the actions of HAL. I see a feature that allows moving fuel aft to get a better configuration that relieves the HS/elevators from exerting a donward force. So we get lower "trim drag", and it's a good thing a lot of the time.

The cee gee of AF447 was nowhere near the aft cee gee that results in an unstable longitudinal static stability condition.

Thanks to Turbine, I have a limited explanation on the B777 control law philosophy. The thing seems to be more biased to AoA than to a gee command corrected for pitch. So this provides the "feelings" that many of us learned to deal with long ago. Trimmed for a low AoA and holding backstick, then release the stick and the sucker goes nosedown. And vice versa.

The actions of a cosmic FBW system that overcomes the basic aero characteristics of the jet can be neat, but can be fatal.

I can only speak from my experience in the first fully FBW jet to be fielded in more than a handful of airframes or test vehicles. The Earth was still cooling. Anybody else here with such experience would be welcome to contribute to this discussion.

As with the 'bus, our FBW system was heavily biased toward gee command. We didn't see a significant AoA contribution unless pulling hard and getting slow. So we were basically speed neutral in level flight and only basic aero drag kept us from getting faster and faster or or vice versa. No big deal, as we didn't spend hours of "monitoring" the computers.

The gee command of the 'bus is a major factor in moving the THS. The system tries to reduce the pilot stick pressure for the commanded gee. NOT THE AoA!!!!! Boeing seems to like the AoA for trimming.

So the BEA report correctly points out that the jet would have gone into test pilot conditions with the pilot commanding neutral stick once the pitch attitude and power setting allowed it to enter a stall.

The 'bus FBW laws' emphasis upon gee command and the lack of attention to AoA inputs was a major contribution to this incident. I completel;y agree with the others here that holding initial attitude and power for "x" seconds would have saved the day.

I would hope that the major carriers would try to expose their pilots to some of the edges of the envelope either in the sim or the actual jet.

john_tullamarine

40 + degree nose attitude (I presume your reference to "down" was intended to be up for the pitch attitude but down for the resultant path vector ?)

I don't think that your observation is quite right .. although I may have missesd a subtlety in your point along the way ..

I would have to wade back through eternity to find the numbers from earlier posts but, as I recall,

(a) the aeroplane was moderately nose up in pitch attitude

(b) the ball would have looked reasonably normal-ish albeit much too nose up compared to normal flight and pitch values

(c) the flight path vector (again I can't recall the specific term for this aeroplane) was showing a steep descent ..

(d) and the two, taken together, gave an approximation of alpha .. which was the relevant 40-odd degrees measure.

That is to say, presuming that the instrument was presenting a picture, the ball indication would have been instantly obvious to any competent I/F pilot and the Commander probably (? - just my thoughts) read the ball right straight away but, with the overall bizarre situation for an airline pilot .. it was going to take him a little while to figure out just what in the blue blazes was going on and where his sidekicks had got the aeroplane to in the few minutes that he was out of the cockpit.

.. it was a great tragedy that the situation didn't give him the time he needed to

(a) figure out the story, and

(b) fix it

before the pond cut short his options.

In which case we wouldn't have this marvellously huge expanse of threads and posts on a single topic.

rudderrudderrat

Hi John,
I don't think the flight path vector (bird) was ever displayed. The HDG/VS TK/FPA button on the FCU needs to be pushed in order to bring up the display. I can't find any reference saying they did.

Normally a crew would ask for "FDs off, bird on" - but this crew kept their FD switches on, and seem to have been trying to follow erroneous FD commands (e.g. VS +1400/min during the descent Page 96 Final report).

HazelNuts39

Question for our french-speaking posters:

2 h 11 min 42,5 bruit d’ouverture de la porte du cockpit
2 h 11 min 42,5 CPT: eh qu’est-ce que vous (faites)
2 h 11 min 46,7 bruit similaire à la fermeture de porte
2 h 11 min 52,6 CPT: alors tiens prends, prends ça
2 h 11 min 55,0 PNF: prends ça là prends ça (*)
2 h 11 min 57,0 PNF: essaye de prendre ça
2 h 11 min 58,2 PF: Je… j’ai, le problème c’est que j’ai plus de vario là

Looking at the picture of the standby instrument posted in Turbine D's post #923:
Are the captain and the PNF pointing at the standby instrument, and is the PF replying that his problem is that the standby instrument doesn't have a VSI?

Turbine D post #923

john_tullamarine

I don't think the flight path vector (bird) was ever displayed.

I would have to wade back into the depths of the threads to establish that .. perhaps I had misread that the indication was there. However, if not, then I would have expected the Commander to have asked for it once he figured out the lilkely scenario .. the pond cut his opportunities short ...

HazelNuts39

JT,

From the final report, paragraph 1.16.5.6:

john_tullamarine

Thank you, kind sir.

CONF iture

That could make sense, I agree.
But due to the position of the ISIS on the dash, it is usually the job of the guy seated on the captain's seat to assume the controls. Telling the guy who is seated on the right side to fly on the instruments facing the guy seated on the left side is not logic, especially when the comment is also from the guy seated on that left seat.

But the comments following yours are also very interesting :
2 11 58 PF: le problème c’est que j’ai plus de vario là
2 12 01 CPT: d'accord
2 12 01 PF: j'ai plus aucune indication
2 12 02 PNF: on a aucune indication qui soit valable

The vertical speed indicators when indicating something were probably not indicating a steady 10000 feet/min in descent. In relation to the roll of the aircraft, those indications were vastly varying between themselves. How were the altitude indicators ... ?

Lyman

Is there a possibility that Captain was reading and prompting PF with ISIS due PF's horizon was n/a, INOP?

bubbers44

john, you are right, 40 + angle of attack after the pitch went from +15 degrees to about - 10 degrees. Unless the captain saw how they managed to put them selves in that position he would have difficulty sorting it out initially not having ever seen it before.

The flight recorder shows their IAS dropping off drastically when they pitched up. Wouldn't their flight instruments tell them the same thing with a frozen pitot tube? Did they just follow the FD? If so maybe being an old farght isn't so bad after all.

BOAC

CONF iture

But at least the rule was clear and unambiguous : Under manual flying it is the pilot job to trim.
Under manual flying by Airbus it is different, sometimes I trim for you, sometimes I don't, and sometimes I even won't tell if I don't : Perpignan

Once again, the stick was NOT held back for the period of time the THS rolled back.

IMO there is something very critical here :
Regarding the specificity of the flight law, for the THS to stop rolling back, even a push on the sidestick (G demand below 1) should have been greater or in this case lower that the measured G for the period and that measured G was already below 1.0
In other words, even a push on the sidestick, if it was not strong enough, could have seen the THS still moving further up.

RRR Gums and RF4 may have made comments in that direction earlier. Tell me if I have misunderstood you please.

Far from it, very far.

The position of the THS is absolutely relevant to the outcome of that flight.
It is also part of the cause.

gums

@ Conf

Way I read it is that the 'bus is primarily a gee command, so pulling or pushing commands the gee. Not like the gee command we had in the Viper, which had an AoA limit input, but a one gee command corrected for pitch attitude. So at any attitude except zero, the gee command is less than one gee.

I shall admit that pitch rates and gains are in the mix, but not AoA unless in the primary control law. And this disturbs me.

No doubt that the THS trim logic "helped" to keep the nose up attitude of the jet all the way down. Even releasing the stick would have kept the THS full nose up, and the BEA report mentions this aspect of the flight control laws.

I highly respect all the "heavy" drivers here, and I have learned a lot from the last two years of dialogue. I agree with Bubs and JT, et al, that the Captain could not figure out how the jet got to its condition without going thru the whole sequence. Just ran outta time.

I would not expect the average "heavy" driver to figure out the problem in a few seconds. No offense to most of you, but realize that the two folks up front were born and bred in the 'bus, and "you can't stall this thing", right?

I shall still maintain my position that the 'bus control laws need a heavier emphasis upon AoA, much like the B777 laws I saw in Turbine's link. It is not hard for HAL to see the AoA inputs and use them to help with the flight director displays and the "protections", regardless of the impact pressure on the pitot tubes. There are too many sensors on the jet to use for graceful degredation, IMHO.

As in my last post, I see a super aero design in the 'bus, and it has no pitch co-efficient problem that results in the classic "deep stall". In short, the jet would have recovered given the proper control commands. But ya gotta realize what is happening, ya think?

Lastly, I doubt that the current 'bus drivers will ignore the AF447 incident's lessons. YOU CAN STALL THE THING if in a reversion control law. If AP disconnects then hold what ya got for a while until you figure out what is happening. Don't depend upon HAL to correct for any of your incorrect commands, but think like you are flying a Cub or Cessna. And the beat goes on.

DozyWannabe

Er - the trend over time (which is the criterion for autotrim movement of the THS) shows that the stick was held at least half-back for the majority of time the THS moved to the full-deflection position, and it was the 35 seconds it was held fully-back which kept it there:

CONF iture

I would go further than that :
Even releasing the stick would have brought the THS further nose up.

DozyWannabe

It depends how long for, and what attitude the aircraft was at when the hypothetical stick release happens.

It went all the way back in this case because the elevators were no longer sufficient to maintain the requested attitude as the speed bled off. The THS had moved approximately 5 degrees nose-up at the apogee of the climb. From that point onwards, the stick is held halfway back by the PF for a further 15 seconds, released for about 4 seconds with a small "blip" forward and then slammed against the back stop for an eye-watering 34 seconds. In short, the THS went where it was told to go by the PF. If he'd released the stick prior to the apogee, it would likely have stayed at a max of 5 degrees NU.

Put another way, the pitch command ratio (NU:NEUTRAL:ND) over the 53 seconds following apogee/stall is approximately 49:3:1 in seconds - which is an overwhelming trend towards nose-up.

Now - an interesting sim test would be to try stick-neutral just prior to the apogee, at the apogee and after the apogee (at the point where the PF slams the sick against the back stop) and see what the autotrim system makes of it. I'd be very surprised if the BEA haven't done precisely that, but a second opinion is always useful.

gums

C'mon, Doze, the pilot does not "command" the THS. The THS moves to reduce stick inputs for the commanded gee. HAL does this, not the pilot unless in one of the myriad of control laws.

As I recounted in an earlier post, our primitive FBW system was a gee command like the 'bus until we hit the AoA bias/limit. You could "trim" for two gees and due to the awesome visibility look back to see what the hizontal stabs were doing. The suckers would tilt down to get the nose up, then settle out until reaching the AoA limit ( "protection", if you will). In short, we had a full-time THS that tried to get to our trimmed gee, not AoA. At the AoA limit the stabs would then move the other direction to keep the AoA under 27 degrees or so until they were fully deflected for nose down pitch. Result was trimmed gee or one gee and max AoA, and falling like a rock.

My feeling is that all 'bus drivers need to see what HAL is doing to "help" them from getting into problems. All the "help" can hurt you when flying where you are not used to.

DozyWannabe

Normal and Alternate Law pitch commands are for *flight path*, not G.

(which is, I believe, the crux of CONF iture's idea behind the THS trying to maintain flightpath even if the PF let go - in all honesty the answer to that is outside my sphere of knowledge)

The computers can't do it unless the pilot tells them to.

(and in this case the pilot was still trying to command a climb for almost a minute after the aircraft had stalled and begun to descend - the computers were simply trying to comply because they weren't specified with this scenario in mind)

You can see what autotrim is doing at any point by looking at the trim wheel. Of course, that's no good if the pilot hasn't been told where to look...