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AF 447 Thread No. 9

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AF 447 Thread No. 9

Old 14th Jul 2012, 18:53
  #381 (permalink)  
 
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SS Take Over

If LHS PNF was convinced that he needed control all he needed to do was push SS forward while at the same time pressing and holding the take over button on the SS and saying, "I have control". If RHS PF does not respond in time honoured aviation fashion, "You have control", PNF keeps the TO button pressed.

If I remember correctly all the time the to button is pressed you have control and after 30secs holding it pressed the opposite SS is latched out.

Correct CRM, I have/You have, allows takeover without the need to lose the other SS as the taking over pilot can release the TO button before 30secs has elapsed.

Press and hold, until release is acknowledged, is taught for capts taking over in the event of a botched landing from the other seat!
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Old 14th Jul 2012, 19:12
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Correct CRM, I have/You have, allows takeover without the need to lose the
other SS as the taking over pilot can release the TO button before 30secs has
elapsed.
In a co-operative handover, does a Priority button even need to be pressed? E.g. FO flying, Captain puts his hand on the stick, calls "I have control" or "my aircraft" or whatever, FO releases his stick.
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Old 14th Jul 2012, 19:19
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On a yoke-equipped aircraft with one pilot pushing and the other pulling, which input does the a/c follow?

Hi DL-EDI....

Which input? There is only one, the columns act as one. The efforts of two pilots result in one command only. They are mechanically connected.


"If LHS PNF was convinced that he needed control all he needed to do was push SS forward while at the same time pressing and holding the take over button on the SS and saying, "I have control". If RHS PF does not respond in time honoured aviation fashion, "You have control", PNF keeps the TO button pressed."

Hi 1066....You presume that the system will be followed, when it has built in traps that depend on CRM. With or without CRM, a yoke equipped a/c cannot split command, mechanically, it cannot happen, and is independent of the sanity or skill of either pilot.

Last edited by Lyman; 14th Jul 2012 at 19:23.
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Old 14th Jul 2012, 19:26
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Which input? There is only one, the columns act as one. The efforts of two
pilots result in one command only. They are mechanically connected.
Well, that was kind of my point.

So what's the difference between that situation and the Airbus method of producing one command only, apart from not giving preference to the pilot with the stronger arms?
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Old 14th Jul 2012, 19:34
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So what's the difference between that situation and the Airbus method of producing one command only
The "Airbus method" is not of one command only, like most of us know.

If you mean just the algebraic summation it is true, but the critical point are subtle inputs from either side, without knowing of the other pilot. And this happens day by day.

Last edited by hetfield; 14th Jul 2012 at 19:35.
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Old 14th Jul 2012, 19:40
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Howdy...

It is perhaps easier to consider that the two systems are offering two ways to input command. Both have two stations, one has split input engineered into it. In an arse about look, consider that the yokes are made smaller and put on either side of each pilot. That is architecture alone. Now, consider the yokes can be manipulated differently, with simultaneous and differing command, but to a computer?

In making everything computer dependent, Airbus has missed something, the need for Bulletproff CRM. The possibility exists that command is in some cases made murky by a design, which should never be the case?

Split input engineered into it? Why yes, else "summed solution" would not exist. Can one say the split input is an artifact of poor design? Without question. For that to be considered wrong, one would have to say split input was inadvertent. I think the designers might take offense....
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Old 14th Jul 2012, 19:58
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Now, consider the yokes can be manipulated differently, with simultaneous and
differing command, but to a computer?
Airbus scenario - One pilot pushes his stick to 100% nose-down while the other pilot pulls his stick to 100% nose-up.

Boeing scenario - One pilot tries to push the yoke to 100% nose-down while the other tries to pull the yoke to 100% nose-up.

Assuming both Boeing pilots have the same strength, wouldn't the net result in both cases be zero pitch input? Isn't it the case that neither system is deliberately designed to allow two pilots to engage in a prolonged fight for control?

The possibility exists that command is in some cases made murky by a design,
which should never be the case?
I'm no aviation expert but, based on my IT experience, I'm not sure that algebraically summing two inputs is a particuarly challenging task for computers.
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Old 14th Jul 2012, 21:54
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When flight path stabilized use the UAS checklist using pitch and thrust.

Level at FL350 seems pretty stabilized to me. The pitch up and climb power were meant for terrain clearance not for high altitude autopilot and airspeed loss. We can't help AF447 but maybe this investigation will help some other pilot that loses airspeed and autopilot in high level flight to not make the same mistake.
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Old 14th Jul 2012, 22:04
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DL, that is what the palm of your hand is for. To smack the FO so he lets go of the wheel. Now you have control. Works every time.
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Old 14th Jul 2012, 22:18
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Boeing scenario - One pilot commands 100% nose-down, the other 100% nose-up.

In the Boeing FBW planes (777, 787) where the yokes are not mechanically connected to the control surfaces, is there a take-over button to resolve the conflict?

Last edited by kwateow; 14th Jul 2012 at 22:22.
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Old 14th Jul 2012, 22:20
  #391 (permalink)  
 
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Originally Posted by OK465
I'm having a problem with understanding that an A/P pb will physically engage in 'latched' ALT2 when it wouldn't engage during the period of time that the condition precipitating the latching was in effect.
Seems that FCS gives up restoring itself back to normal law after it detects long lasting ADR disagreement, however AFCS keeps checking indefinitely and will restore itself as soon as two ADCs agree, not necessarily at correct value. Page 86 of the report refers.

Originally Posted by OK465
If you were able to get the A/P pb to engage in ALT2, what would the FMA displayed lateral steering mode be in roll direct? Same as roll alternate? Blank?
Probably NAV, HDG or TRK. Airbus AFCS is just an AFCS, only special thing about it is output; it doesn't go to autopilot servos but to FCCs. I suppose it doesn't care if its roll commands are obeyed by moving the spoilers and ailerons with constant roll rate or constant deflection. I suspect that AP doesn't work in direct law is because FBW has no control over pitch trim in it.

Originally Posted by Organfreak
There's always room for improvement, whatever the make of the aircraft.
Yup, but they don't come about just because someone has wished for them and they never come without a price.

Originally Posted by Lyman
That the stick shaker is a life saver
So are a parachute and a helmet but you won't see me wearing those when flying passengers.

Originally Posted by Lyman
is trained in approach to Stall syllabi
On the aeroplanes equipped with it!

Originally Posted by Lyman
and is found on your very own aircraft
Because during certification, her natural stall characteristics were found wanting so they had to be supplemented by the artificial means!

Originally Posted by Lyman
You fly a turboprop, a T tail, I assume. That is a complex platform, and in challenging conditions, I propose that your aircraft so equipped, is a safe one?
Safe aeroplane with totally unsafe natural stall characteristics. How about that?

Originally Posted by Lyman
the outcome may have been better if the stick turned into a buzzing snake in her pilot's grip?
BEA actually performed the study to determine what it felt like as the AF447 approached the stall:

Originally Posted by BEA final report on AF447, English version, page93
Airbus subsequently flew special flights to collect more accurate data at high angles
of attack and with an aircraft configuration close to that of the accident (mass, flight
level, Mach, etc.). These tests made it possible to refine the preliminary correlations
and to establish that the level of buffet was considered to be a deterrent by the test
pilots when the angle of attack was about 10°, corresponding to normal acceleration
amplitude of 1 g at the pilot’s seat. This angle of attack was reached at about 2 h 10
min 57 s during the accident flight.
What are the chances that the pilots that ignored 1G amplitude shake as the sign of impending stall would pay attention to "buzzing snake"? I hope this lays the notion of stick shaker being useful on A330 to rest.

Originally Posted by Lyman
The 330's Stall was entered in extreme fashion, quickly, and without the nose drop and falsely advertised Buffet from Stall that the Airframer sold the regulator on when begging for what you describe as "dispensation" from Shaker install.
See previous entry.

Originally Posted by Lyman
I am amazed that such a seasoned pro would continue to say that the shaker would have been of no use.
With a little help from the red warning at the bottom of this page, your posts amaze me no more.

Originally Posted by DL-EDI
In either case, wouldn't continued wrestling with the the controls suggest a bigger issue than how the logic works?
Depends on controls architecture. On some aeroplanes you may end up with split controls and each side flying just one elevator, completely independently of the other. Sounds fun, eh?

Originally Posted by DL-EDI
In a co-operative handover, does a Priority button even need to be pressed?
No.

Originally Posted by Lyman
a yoke equipped a/c cannot split command, mechanically, it cannot happen, and is independent of the sanity or skill of either pilot.
It can split. It can happen. It is not independent, especially in the wrestling over controls cases. Priority button is very neat way of taking the control away from the captain Gonenuts.

Originally Posted by Dl-EDI
I'm no aviation expert but, based on my IT experience, I'm not sure that algebraically summing two inputs is a particuarly challenging task for computers.
That's just what they do but it is very, very wrong way to fly an Airbus. Only one pilot can fly her at the time, be it left, right or auto, this feat is just there to ease the hairy control handovers, before PiC clearly designates who will fly.
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Old 14th Jul 2012, 22:44
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bubbers44:

DL, that is what the palm of your hand is for. To smack the FO so he lets go of the wheel.
Though in either type, that might favour a married FO, with a large wedding ring on his/her inboard hand... at least until they're back in the office... and it would only happen once.

kwateow:

In the Boeing FBW planes (777, 787) is there a take-over button to resolve the conflict?
They have inter-connected yokes.

Clandestino:

Thank you - I didn't think transferring control was as complicated as some think (no-one in particular).

That's just what they do but it is very, very wrong way to fly an Airbus. Only one pilot can fly her at the time, be it left, right or auto, this feat is just there to ease the hairy control handovers, before PiC clearly designates who will fly.
Indeed but some seem to think there's something dangerous about the Airbus dual-input logic when, functionally, it's not that different. As I said, if you get continued conflicting dual-input then you've got bigger issues to worry about.
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Old 14th Jul 2012, 23:27
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OK465:

I'm having a problem with understanding that an A/P pb will physically engage in 'latched' ALT2 when it wouldn't engage during the period of time that the condition precipitating the latching was in effect.
AP was disconnected due to (dual) ADR loss, AS gains could not be established.
Once the (dual) AS returnes, the gains can be established again.

The AP has it own gains, rate- and amplitude limitations build in, it don't need the NORMAL LAW or whatever remaining protections in ALTERNATE.

AP commands a separate pitch deflection order for elevator (DQ) and THS(DQT) to FCPC in control.
For roll command there is a separate roll order(P) for ailerons and spoilers.
Yaw control command is separated in (Ytrim) and (Ystab).
All are deflection! orders.

If you were able to get the A/P pb to engage in ALT2, what would the FMA displayed lateral steering mode be in roll direct? Same as roll alternate? Blank?
After 02:10:46 it would return in HDG or TRACK because that are the only SELECTED lateral modes available.
AFAIK with current HDG or TRACK as default.
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Old 14th Jul 2012, 23:52
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A33Zab: Thank you, sir.

Should the STATUS page eventually reflect availability of the A/P (by exclusion) even though ALT2 initially latched with AP 1+2 displayed as INOP on the STATUS page?

Is the displayed A/P STATUS and availability updated automatically or does it have to be cleared?

(edit: thanks clandestino also, and is roll direct an FCSC function in this case? additional edit: It occurred to me that doesn't really matter if the commands are deflection orders. Thanks again.)

Last edited by OK465; 15th Jul 2012 at 00:19.
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Old 14th Jul 2012, 23:58
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DL, you have to survive so fighting control over the aircraft is not an option. The PIC normally takes control in a conflict because he is in command. Sometimes the FO has to take control if the PIC is going to kill everybody. I only had to do this once as an FO on a 4 engine corporate jet and forced a go around.

I assumed I was fired but the chief pilot thanked me for saving a totally botched approach on a short wet runway. We were too high to not have an overrun so I went max power and went around on his leg.
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Old 15th Jul 2012, 00:35
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A33Zab re Post #362

Many thanks for the logic schematic which certainly is an improvement over that described in FCOM / FCTMs.

With the logic shown, the conditions for A/P engagement are clear, and I assume that the A/P Auto OFF conditions, i.e.
if abs(φ) >45°,
or θ <-13°, or θ >+25°,
or CAS < VLS,
or CAS >(VMO/MMO or VLE/VFE)
will take precedence once the A/P has been engaged?
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Old 15th Jul 2012, 00:43
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@OK465:

Should the STATUS page eventually reflect availability of the A/P (by exclusion) even though ALT2 initially latched with AP 1+2 displayed as INOP on the STATUS page?

Is the displayed A/P STATUS and availability updated automatically or does it have to be cleared?
As a general rule ECAM messages and INOP status are cleared automatically when the fault or inop conditions are not active anymore.

(edit: thanks clandestino also, and is roll direct an FCSC function in this case?)
If you allow me,

No, roll direct is part of ALTERNATE (ALT2x) control of the FCPC.

FCSC ALTERNATE YAW/DIRECT control becomes active if all 3 FCPCs failed to control in DIRECT.
To set that in perspective:

Priority:
1 = FCPC #1 in NORMAL
2 = FCPC #2 in NORMAL
3 = FCPC #3 in NORMAL
4 = FCPC #1 in ALTERNATE (active @ AF447)
--
7 = FCPC #1 in DIRECT
--
10 = FCSC(#1 & #2) ALTERNATE YAW/DIRECT
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Old 15th Jul 2012, 00:52
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Do pilots follow unknown FD commands and if so for what reason? Isn't the checklist saying 5 degrees nose up and climb power until at a stabilized altitude which they were at at FL350 and use UAS and thrust charts to continue. Seems they were already stabilized.
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Old 15th Jul 2012, 00:58
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@mm43:

Correct, there are small deviations in the values to engage and the values to automatically disengage.

Yours are indeed the disengage values.

to use your format:

AP Engage is inhibited:

if abs(φ) >40°,
or θ <-10°, or θ >+22°,
or CAS < VLS,
or CAS >(VMO/MMO or VLE/VFE)
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Old 15th Jul 2012, 18:16
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Originally Posted by Lyman
Which input? There is only one, the columns act as one. The efforts of two pilots result in one command only. They are mechanically connected.
Not exactly true on advanced airliners - remember the EgyptAir 990 case highlighted an unforeseen problem with the 767's interconnection, namely that when one pilot pushed and the other pulled, the result was split elevators and immediate departure from controlled flight.
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