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-   -   AF 447 Thread No. 10 (https://www.pprune.org/tech-log/493472-af-447-thread-no-10-a.html)

jcjeant 2nd Sep 2012 21:19


Alpha max is the highest alpha that the flight control computers will allow for a given configuration and weight; it provides the max lift coefficient.
It would be surprising Airbus have not taken into account a safety margin
For me I read through this to mean:
Alpha max is the highest alpha that the flight control computers will allow for a given configuration and weight; it provides the max lift coefficient (with a safety margin)
In all constructions or system .. it's always a safety margin ... (factor)
DW

When hand-flown, the last of these inputs is indeed human.
I suppose you mean First instead Last
You have First is Last in a single command when pulleys and cables are used for transmit the inputs

Lyman 2nd Sep 2012 21:42

Technically, the impetus for control deflection is commanded by code created by a surrogate, a human. So first is last....

DozyWannabe 2nd Sep 2012 22:19


Originally Posted by jcjeant (Post 7392699)
It would be surprising Airbus have not taken into account a safety margin
For me I read through this to mean:
Alpha max is the highest alpha that the flight control computers will allow for a given configuration and weight; it provides the max lift coefficient (with a safety margin)

You might be right, but to my reading the difference between the alpha protection threshold and alpha max *is* the safety margin. In fact it's the primary safety margin. There is a secondary safety margin between alpha prot and alpha max, which is the alpha floor trigger value.

None of this is relevant to AF447 though, because protections were out of scope.


DW
I suppose you mean First instead Last
You have First is Last in a single command when pulleys and cables are used for transmit the inputs
I wasn't talking about that sense, I listed three primary inputs to the autotrim system, of which the third (and last) was the flight control commands which are human under hand flight:

Code:

IN            PROCESS    OUT

Elv.Position|------------|     
 ----------->|Autotrim    |Trim Cmd

THS Position|            |------>
 ----------->|            |(to THS &
 Pr.Flt.Ctl  | System    | trim wheels)
 ----------->|------------|

(Yes it's a gross oversimplification, but I hope it makes what I was trying to say clearer... - EDIT : Apologies for it being a little wonky - the code tag seems to behave differently between preview and posting for real...)

A Primary Flight Control input which is neutral is still an input to the autotrim system - it cannot make flightpath decisions in isolation (unlike autoflight).

bubbers44 3rd Sep 2012 00:01

None of this applies to this incident. Two pilots let an aircraft go into a full stall for no reason because the autopilot clicked off. End of story.

jcjeant 3rd Sep 2012 00:15


None of this applies to this incident. Two pilots let an aircraft go into a full stall for no reason because the autopilot clicked off. End of story.
Methink .. all have agreed with your motto since the release of the BEA interim report N°3
This was indeed the end of the story for all the human souls aboard AF447
I think the mean of the discussion(s) is to know (or analyze) why this happend ....
IMHO

DozyWannabe 3rd Sep 2012 00:42


Originally Posted by bubbers44 (Post 7393006)
None of this applies to this incident. Two pilots let an aircraft go into a full stall for no reason because the autopilot clicked off. End of story.

Bubbers, it's not that simple. It may be comforting to paint it as a symptom of degrading flying skills in the "Magenta Line" era, but some of the evidence contradicts this. For example, the PF was a sailplane pilot (ref: Final Report [English] p.28) and by rights should have had a better working knowledge of aerodynamics and flight envelopes than many on the line.

I've been a dedicated follower of aviation and aviation safety for most of my life, and one of the things I've come to realise over the years is that most fatal accidents that do not have a direct technical cause are not indicative of the crews in those cases being generally sub-par, but tend to stem from making an error or series of errors that they would not normally make. I like to think this is because the minimum level of competence in a line pilot is actually pretty high by the standards of a lot of professions (case in point, the Captain of ColganAir 3407 was considered to be of below-average ability and yet it took levels of fatigue that would not be permitted in any other safety-critical industry to get him to make a fatal mistake).

So the big question is as it has always been - why? Why did the PF pull up into a zoom climb, pull up into a stall and for the most part keep pulling up all the way down? Why did neither of the other crew members try to stop him? Why the seemingly complete breakdown of CRM?

Unfortunately, like other accidents in which some crew actions seem -at least at first glance - so aberrant as to border on inexplicable, I don't think there'll ever be answers to these questions that will satisfy a majority of people, let alone everyone.

CONF iture 3rd Sep 2012 02:10


Originally Posted by Dozy
[EDIT - I wasn't kidding about going too far off-topic, I really don't want to derail a discussion on an accident where the protections were inhibited by talking about protections...]

Don't expect to write anything on the subject without being challenged at least.


Probably not the greatest source, but the best I could find at short notice:
At long notice, anything better ?

DozyWannabe 3rd Sep 2012 02:27

The "challenge" isn't incompatible with anything I've said - Alpha Max is the (effective) constant, Alpha Prot and Alpha Floor thresholds are variables computed from Alpha Max taking the aircraft's attitude and flightpath into account.

The FBW system does not have any concept of "stall" or "operational ceiling" programmed into it as discrete entities, even in Normal Law (it's not that 'smart'!) - just a set of variables that should not be exceeded. Doing so will trigger protections in Normal Law and warnings in Alternate and below.

CONF iture 3rd Sep 2012 03:54


Originally Posted by Dozy
The "challenge" isn't incompatible with anything I've said

Yes it is.
Same reply ...

HazelNuts39 3rd Sep 2012 08:11


Originally Posted by Dozy
Alpha Prot and Alpha Floor thresholds are variables computed from Alpha Max taking the aircraft's attitude and flightpath into account.

Just out of interest: are you sure the margin between alpha-prot and alpha-max varies with attitude and flightpath?
EDIT:: Perhaps you are referring to the phase-advance of the angle of attack signal?

Hunter58 3rd Sep 2012 11:11

Dozy

Just because the PF was also a glider pilot does not mean he did make the mental transition from aerodynamic knowledge of gliders into his big metal as you take to assume. Same as you don't make that same transmission from a standard car into a truck.

I do not believe that someone can make such an intellectual shift from one thing to another under stress so easily, especially when the environment and 'feel' of the location is so completely different to one another.

Linktrained 3rd Sep 2012 17:42

PF was a glider pilot... but it is not clear at what level. A French Brevet B used to require a flight making two turns before landing. A Brevet C required a longer flight with a gain of height for 5 minutes, both followed by a safe landing. PF already held a professional pilots licence, so these first two grades should be easy. He may have done more. I do not know. (It may be that a very, very high performance glider must have Mach limitations, too...)

PF was concerned apparently, about speed and "odd speed/ sounds" (my words) .

It was noted several months ago that the power was reduced from TOGA to 61% N1 for a couple of seconds and the NU decreased for this short time, IIRC.

Then power was restored to TOGA for the remainder of the flight. Were any comments made, by BEA on this or is it mentioned on the CVR ?

hetfield 3rd Sep 2012 18:05

For how many (more) years will this be discussed here?

The two pilots up front goofed it up!
They goofed it up in many ways.

You know it, I know it, this accident was totally avoidable!!!!

No rocket science, just basic flying skills.

RetiredF4 3rd Sep 2012 19:57


hetfield
For how many (more) years will this be discussed here?
Until the next accident happens?


The two pilots up front goofed it up!
They goofed it up in many ways.
The captain as well, or what reason do you have to let him of the hook?


You know it, I know it, this accident was totally avoidable!!!!

No rocket science, just basic flying skills.
There are no unavoidable accidents. Any accident has a cause and contributing factors.

When everything is that clear to you, then you may answer those questions,

-why their company didnīt know about this lack of abilities,
-why no simulator session uncovered those deficiencies,
-why the different captains and FOīs who flew with them didnīt notice any deficiencies,
-why department responsible for issueing the licences didnīt see anything unusual,
- why the regulating agencies didnt see any need for change with AF??

And what is your suggestion to change for accident avoidance in the future?
The crew? The training? The manuals? The procedures? Some systems? Some other ideas?

Thatīs what the ppruner are discussing here, to get something like lessons learned. Thatīs a legal achievement imho on an open forum.

hetfield 3rd Sep 2012 20:36

Franzl,

all I want to point out is, get away with all that tech stuff.

The aircraft, like others, has its flaws.

BUT, BASIC FLYING SKILLS WOULD HAVE PREVENTED THIS VERY ACCIDENT.

There were plenty similar events with a different outcome....

So, if you ask me for suggestions....
PILOTS SELECTION AND TRAINING AND A BETTER MORAL AT AF FLIGHT TRAINING DEAPARTEMENT!!!!!!!!!

Costs money, I know and some skulls:rolleyes:

Organfreak 3rd Sep 2012 21:10


There were plenty similar events with a different outcome....
Like this one....oh, it turned out the same....

Mayday - S11E02 The Plane That Flew Too High - YouTube :eek: :uhoh: :yuk:

(Caveat: I know full well that these programs leave something to be desired, and yet, the facts seem straightforward here.)

john_tullamarine 3rd Sep 2012 23:53

You know it, I know it, this accident was totally avoidable!!!! No rocket science, just basic flying skills.

Not criticising the post at all - the value of this series of threads is the challenge and head scratching which has been on-going. Lessons for all of us along the way, methinks.

However, while many of us may have a view about things .. I don't see any of us expressing a desire to have swapped with the mishap crew for the purpose of demonstrating our presumed superior skills ?

bubbers44 4th Sep 2012 01:38

I flew sailplanes too and towed them. It helps you learn unpowered flight and energy management but doesn't help much in an airliner. Sully flew sailplanes too but it had little to do with his successful Hudson landing. Not stalling the airplane was the answer, but they did.

Peter H 4th Sep 2012 11:45

Sully and glider experience
 

I flew sailplanes too and towed them. It helps you learn unpowered flight and energy management but doesn't help much in an airliner. Sully flew sailplanes too but it had little to do with his successful Hudson landing.
Are you sure? I had always understood that his choice to ditch in the Hudson, rather than aim for a tantalisingly close airport was the critical point in the emergency.

So Sully quickly came up with a good overall strategy [ditch]. Which both pilots then executed admirably.

IMHO a willingness to consider [perhaps even to recognise] alternate landing sites is a necessary part of glider flying. So Sully's background could have influenced him here.

AFAIR experiments on the simulator confirmed the importance of the strategy. Attempts at landing at the airport were mostly unsuccessful -- especially at the first attempt!

HazelNuts39 4th Sep 2012 11:47


A French Brevet B used to require a flight making two turns before landing. A Brevet C required a longer flight with a gain of height for 5 minutes,
Just for accuracy: these brevets are sports grades (pupil level), and have no relation to a glider pilot's license.


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