Lyman

HazelNuts39

In your graph, notice stick placement when "Pulled". The UP inputs are spikes, between them are lapses of linger in Nose Down.

It appears that his UP inputs are a severe reaction to something about the a/c behaviour. Quickly, after pulling up, he immediately reverses and pitches down; the stick does not remain in NU? What might be the cause of this actions? What is he getting from ND that he does not "like"?

Or Lonewolf?

Lonewolf_50

Lyman, this is a guess response based upon a few things.

1. Stated sensitivity of this model acft at high altitudes by people who have flown it, as compared to control sensitivity in the terminal area and altitudes.
2. Change in power setting
3. Pilots initial overcontrol of roll previous to the graph

The above considered, what HN's graph excerpt shows me is that as with roll, the PF doesn't have a good "feel" for his pitch control during seconds 50-85, so there's a bit of over controlling going on. Part of what he's doing looks to me like a response to a pitch change that you'd expect from an addition of power to TOGA, and in part to correct for his own various pitch inputs, corrections, and counter corrections that he apparently isn't happy with. Why unhappy? I think he's aming for a particular pitch attitude and not hitting nor holding it. (Could be wrong).

I am uncertain what pitch attitude he is trying to establish and hold.

From 90-100 seconds, he makes what appears to be a substantial counter correction in the nose down direction with very small counter corrections ... he's milking the stick a bit, trying to avoid overcorrection during that phase, and seems to be making progress in establishing his "feel".

Not sure where the CVR sync's up, but I suspect this particular correction is a response to PNF's warning about 'you are climbing' and 'go down'

Not sure what other forces you are referring to. Seconds 120 to the end, he appears to be deliberately walking the nose down. The graph ends in what appears to me to be the next set of corrections / counter corrections about to start ... though why the SS at - angle induces nose up at the tail end there confuses me ... seeing the whole timeline/graph would probably resolve that confusion.

Lyman

Around the time Captain re-enters, PNF takes control and inputs full left bank. So it seems that both pilots are acting with "Full Stick" ?

HazelNuts, I think I said PF was unaware of his climb, not the Stall Warn.

Lonewolf, not wanting to belabor it, but the graph above null is more reactionary than that below,,,,, it seems to ape the ROLL oscillations, but in PITCH.

The "UP" is spikes, the ND, more flat. So, he's lingering in ND, and spiking NU?

??

HazelNuts39

The zoom climb is not 'sustained'. In response to the PNF's "go down", the V/S is reduced from 7000 fpm at t=25s to 1100 fpm at t=49.

As I read his SS movement, he is trying to maintain 15° pitch but is overcontrolling, like he was earlier in roll. Each time the pitch increases through 15° his SS moves forward, and backwards again when pitch reduces through 15°. From 90-100 seconds, he says "I've lost control ..." and goes all the way to full nose-up to counter the nose-down pitch rate.

Owain Glyndwr

Lyman

I think you've got it about face again - +ve sidestick is ND - he's lingering in NU.
Check the DFDR traces for SS sign convention

DozyWannabe

Correct.

For what it's worth, I think he's chasing something on the ADI rather than the FD (although we'd need confirmation of what the FD would output in that circumstance to confirm or refute).

Lyman

Dozy, Owain. Thanks for the correction. And thanks to HazelNuts39 for his establishment of a rationale in re: PF manual control of the a/c. Something is preventing his establishment of 15 degree Pitch NU, such that he must emphatically get the Nose down? Either way, the spikes to me are a sign of problems in Pitch, just as there were in Roll.

Can we entertain a chronic bias NU, similar to that seen in Right Roll? From the bank traces, just as here with Pitch, there appears (to me), to be just such a bias. Can we conclusively say that the a/c was unbiased in Pitch? Not to include the THS, at least at this point?

Thanks

HazelNuts39

Lyman,
I think we can conclusively say that the a/c was unbiased in Pitch and in Roll.

rudderrudderrat

Hi Lyman,
I'd say the aircraft naturally wanted to lower it's nose as the speed washed off.
It was only due to the PF's mostly nose up ss demands, aided by full nose up stab trim, that he managed to prevent it from lowering.

CONF iture

The point is precisely to emit a logical hypothesis to your earlier question :
"If PF didn't notice stall warning, what caused him to select CLB, then TOGA, go to 15 degrees pitch and actively maintain that until the airplane dropped out of his hand after 40 seconds?"
If the V/S was at 1500 ft/min at the time the FDs reappeared, then the SEL V/S target reopened at that 1500 ft/min. But as the V/S soon was in reduction, the vertical command bar went up, and the PF was proceeding to follow the command and the trim was 'helping' him to do so.

To note that under stall warning the FDs were telling the pilots to pull ...

Owain Glyndwr

I'd say that he held it up there deliberately, but that's only nitpicking

I don't want to spoil the fun, but Clandestino was right when he cautioned against applying 'normal' rules to the stalled state (post #221). I think maybe you can apply some generalisations,i.e behaviour averaged over many seconds, but when you get down to specific time slots there are just too many unknowns.

Just for example; we know that stalling AoA depends on sideslip, so that pitch behaviour near the stall will also vary with slip. We know that the sideslip at high AoA varies kinematically with bank angle, as does AoA itself, so AoA, pitch and sideslip are linked to roll, and we know that the natural lateral behaviour at high AoA is a virtually undamped roll oscillation so that one can expect a sympathetic oscillation in the longitudinal axis. How the dickens can one unscramble that lot without access to some very good data and a powerful computer or simulator? And that is without considering any known possible effects from forebody vortex shedding or wingtip vortex movement over the wing or vortex bursting.

IMHO It just ain't possible - you are wasting your time

Lyman

Thank you both. It may be obvious, I am trying to look at all the inputs, to find something, a clue, as to why: Stall. One needn't remind of the way it looks as a whole. His spike ND looks almost desperate, even angry. So what I seek is an opinion as to why these emphatic ND's? It is in this region of the accident that CRM seems conspicuously absent. If Someone could explain, for instance, why rather than the jerky motions, PF didn't settle on a nudge/ wait format. The aircraft in Pitch cannot move as his stick would, and since the trace of actual Pitch is far smoother than the inputs that command it, why the constant oscillation in stick/hand?

At the least, is it fair to think that the controls and procedures are more reflective of down low, than up high? From the stick trace, the ND inputs seem solitary, again, as if he is angry perhaps at his own over-control? An unfamiliar response from the a.c?

Lonewolf_50

HazelNuts39
OK, I am working on just this bit of the graph.
From time = 0 to time = 25, zoom climb took x seconds.
As I understand it, that was due to more than a single input to the SS.
Am I wrong about that?
It is my understanding that he sustained the climb, but am happy to be corrected.

We enter your graph excerpt at time = 50, after the PNF has alerted him to climb. He's still climbing (sustains his climb), altitude increasing (until stall, and then until momentum peters out).
For this excerpt of the graph, "zoom" climb probably wasn't an apt description. Thanks for that.

By your graph, at time = 105 to about time = 115, he lowers, and keeps lowered, the nose ... or is that the aircraft doing it for him? (See rudderrat's comment). He's moving the SS to get the nose down, or so it seems from the lines. (Even though he says he's lost control, which apparently he has not, at least not in pitch)

As displayed on the graph, his pitch corrections follow the SS graph, out of phase or delayed by a few seconds as the plane takes X amount of time to respond. This ain't an F-16, eh? (Where's gums? )
.
OK, I see where you get that, thanks. Strengthens the idea that he's executing the low altitude shaker stall avoidance procedure.
And then starts walking the SS down, 90-100 seconds, orange line.
And the nose follows.

rudderrat:
Thanks! That paints a slightly different picture for me, and makes aerodynamic sense.

Owain Glyndwr

Wasn't that the time he throttled back to idle? (not shown on HN39's graph)

HazelNuts39

Owain G,
Yes, that is correct. Reading from the graph on page 113, the thrust levers are moved to MCT at t=103, then to idle at about t=107, then at t=128, when the engines have spooled down to near-idle rpm, thrust levers back to CLB, and at t=153 to TOGA.

Lonewolf_50

HN39, thanks. As usual, it isn't just stick/yoke that influences attitude.

We return you to your regularly scheduled program, which today is a live performance of The Pitch and Power Chorus singing their cover of REM's Feeling Gravity's Pull.


...
What the hell is it doing now, ami?
Pitch and power and out of synch here
Pull up, pull up, pull up the sky is open-armed
When the nose stays up, I feel gravity's pull
...

With apologies to Buck, Stipe, Mills, et al ...

A33Zab

@2 h 10 min 47: Selected V/S equals V/S ~ 1500ft/min as CONF correctly stated.

The first 10s the FD bars will be flashing, just before STALL it would have been steady.
During the STALL (negative V/S) the FD order would have been SS UP (in reference to +1500ft/min), Max Guidance is hard limited at 6000ft/min.

However, soft limits are build in and that will make it difficult to determine the exact FD Pitch Bar position.

- FD bar order will never guide into Vmo/Mmo or below VLS (VLS-5 if VLS = target)
was VLS available? and if so was airspeed already below VLS? and if so will it guide to reach VLS?

FCOM section 1.21.00 states:

Quote:

Note :

When flying with FD bars only (AP OFF), the FMGS adjusts the pitch bar so that VLS is maintained.

However, no triple click is generated and the V/S target display on the FMA remains unchanged.

bubbers44

No pilot would use FD command bars in a situation like this unless they were right out of FO school. Experienced pilots do what they have to and ignore FD commands doing what they are trained to do. Everybody knows that.

Lyman

was VLS available? and if so was airspeed already below VLS? and if so will it guide to reach VLS?. From...above, @ A33Zab

Isn't that dependent on ADR's? HazelNuts?

Weren't FD selected to acquire FPV?

OK465

b44:

Any chance of you coming out of retirement?

I'm a big fan of people who know what they're talking about...as a result, from here on in, without you, I'm taking Amtrak, Greyhound or some Italian cruise line.