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AF 447 Search to resume

Old 7th Apr 2011, 04:42
  #3121 (permalink)  
 
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for much of this crash what is often called "meatware" was in control.
Or perhaps attempting to regain control after the flying machine did something "off the wall" while iron mike was in control.
I wouldn't be surprised if the accident was found to be beyond the aircrew's control and experience.
(Other than by not flying into the weather in the first place, but we just do not know what they saw up ahead in their radar at this point.)
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Old 7th Apr 2011, 05:20
  #3122 (permalink)  
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There's a P in PIO... the meat as some of you call it. It took a pilot to rapidly deflect alternating full rudder until it snapped off, in the case of AA587, that was no autopilot causing it.

In fact, I don't think there has ever been an incident where an autoflight/autopilot system was ultimately responsible for the crash of an airplane, so if this system caused departure into an unsalvageable state, that would be a first.

Except, it's not a first for pilots to fly into the top end of a (major!) CB and losing it.

So, when you hear a stampede, think cows, not zebras (for those of us living where there predominantly are cows)...
 
Old 7th Apr 2011, 07:08
  #3123 (permalink)  
 
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There's a P in PIO...
Yes, and autoPILOT has a 'Pilot' in it.
As I stated earlier, it relates to PIO (but is not strictly PIO since no human hand is on the control.)

The human pilot uses variable gain strategies that can be unexpected or inconsistent, but an autopilot must follow its program.

A fly by wire aircraft is being flown by the autopilot essentially until it degrades to a flight law that is strictly pilot directed. Direct law on Airbus is such a pilot directed mode if I recall the system correctly.

Some of you may also be surprised to learn that the A320 aircraft has encountered lateral PIO on a line flight.

PIO is essentially a cliff like change in aircraft behavior that can be brought on by a number of factors. but incorrect gain in the control loop or excessive time lags at the effectors (control surfaces to you) often set it off.

For those that are curious about the subject, find a copy of "Aviation Safety and Pilot Control" published by National Academy Press, ISBN 0-309-05688-8. It is probably more understandable than the textbooks and is moderately priced.
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Old 7th Apr 2011, 07:51
  #3124 (permalink)  
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Originally Posted by CliveL post #3112
To be frank, I can't imagine why anyone would even think of putting the gear down if ditching seemed inevitable
- Clive - your profile does not say much, but I guess you are looking at this from an engineering pov?

As others have said, it is more than possible that there was no 'planned' ditching. From a piloting pov, gear is sometimes lowered to try to control speed, and we do not yet know if this happened. It is useful to me to see if we can establish, from what we can see so far, the likelihood of the gear breaking free after impact rather than being extended AT impact. As with others, I believe the intial impact would have firmly 'trapped' the gear in the up position - whether inertia would have been sufficient to force it through the distorted doors and the uplocks is for physicists/engineers to say. I would hope that someone can see from the pics whether various jacks/angles etc indicate a simple 'free-fall' extension in the water or a planned one? Have we seen both main gear (and nose) yet?

Thank you for the information on gear stressing.
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Old 7th Apr 2011, 07:59
  #3125 (permalink)  
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CONF iture;
Originally Posted by PJ2
Things to note, (as per BEA conclusion that the flaps were retracted
Do they mention the slats ?
It would be interesting if you can see anything in the pictures about the slats as it is part of the procedure to deploy them in an attempt to exit a stall situation.
To answer your questions directly, the slats are not mentioned in either preliminary report, and it's not possible to determine the position of the slats from the photographs available on the BEA site. The wreckage and/or the DFDR will tell us soon enough but there is one possibility although it may be looking too deeply.

If the CAS is higher than 100kts, only the slats are available with a selection of Config 1. So for normal operation in flight, the position of the flap drive does not tell us anything about the slats.

If the CAS is below 100kts, selecting Config 1 will bring out the slats and also bring out the flaps to "1", (8.5deg), which is a normal takeoff configuration in, (Config 2 and 3 can also be used for takeoff).

Since the SFCC [for others not familiar, Slat - Flap Control Computer] gets its speed information from the three ADIRUs, [Air Data and Inertial Reference Units] and we know that there was a loss of airspeed data in the three ADRs we don't know how the SFCC would respond to a crew selection of flap 1.

When recovered, I think it will also be interesting to see what the THS [Trim Horizontal Stabilizer] or screwjack position is.

BOAC, we have seen both main gears but not the nosewheel.

PJ2

Last edited by PJ2; 7th Apr 2011 at 08:13.
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Old 7th Apr 2011, 08:16
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Sadly, when it's all said and done, I think we might discover that the THS was at or close to the full NU position and in the "Use Manual Trim Only" mode at impact. This THS flight control degraded mode freezes the THS (trim wheel control only) and thus overpowers the pitching moment of the elevator control power via the sidestick for pitch changes.

I would suggest that at CG positions of say 34-38% which are typical of this type in cruise, that if the THS attained a position of full NU (or close to full NU), that it would cause the a/c to stall and furthermore not allow any chance of stall recovery...unless manual use of the pitch trim is used to reposition the THS in the ND sense.

Just speculation and my humble opinion of course...
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Old 7th Apr 2011, 08:19
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Since the SFCC [for others not familiar, Slat - Flap Control Computer] gets its speed information from the three ADIRUs, [Air Data and Inertial Reference Units] and we know that there was a loss of airspeed data in the three ADRs we don't know how the SFCC would respond to a crew selection of flap 1.
Hi,

isn't there a gear safety valve on A330 (I'm not current on 330)?
If so, where does it get the speed from?
What happens if no valid data signal?

Thx
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Old 7th Apr 2011, 09:54
  #3128 (permalink)  
 
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Shear pin

Originally Posted by CliveL
The gear support structure has a shear pin designed to allow the gear to break cleanly in the event of a crash (9g longitudinal). This is so that it doesn't tear a great hole in the fuel tanks.
The rear attachment of the pylon of wing-mounted engines incorporates a shear pin. It is designed to break when the engine is hit from below in a crash, and allows the pylon and engine to pitch up and depart over the wing, so as to avoid rupturing the fuel tank. I have difficulty imagining a similar function of a shear pin in the main gear support structure. Could you explain that in more detail?
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Old 7th Apr 2011, 10:28
  #3129 (permalink)  
 
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Automatic trim

Originally Posted by FlexibleResponse
if the THS attained a position of full NU (or close to full NU), that it would cause the a/c to stall and furthermore not allow any chance of stall recovery...unless manual use of the pitch trim is used to reposition the THS in the ND sense.
I believe you are referring to the A320 accident at Perpignan. In that accident the condition you describe developed because the AoA vanes were inoperative. If those vanes are free to move, automatic trim stops short of the stall AoA. I believe that at that point it is still possible to recover by normal use of the elevator.
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Old 7th Apr 2011, 10:50
  #3130 (permalink)  
 
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Inertia (Momentum) of MLG assembly

Quote from BOAC:
As with others, I believe the intial impact would have firmly 'trapped' the gear in the up position - whether inertia would have been sufficient to force it through the distorted doors and the uplocks is for physicists/engineers to say.

Just a reminder that each A330 MLG is a massive (heavy) structure - one of the biggest in the business - whereas the main door you are considering is suitably large, but made of a composite material about as light as fibreglass. I'm also not convinced that this material could wrap itself around the bogie (wheel truck) without shattering.

It is true that pilots occasionally use the gear as an airbrake, and - in extremis - even to provide lateral stability. A double-engine failure would probably prevent the gear being subsequently retracted for a ditching, due to the effect on hydraulics, even if the APU could be started in good time. Once down, therefore, it would probably have remained down. So: was it?

CliveL's 9g longitudinal shear-pin - or something equivalent - must prevent an extended MLG from compromising the rear spar (or my "Bermuda Triangle"). The fact that the rear spar and MLG are still visible ensemble in the BEA photo convinces me that the gear was not in the extended position at the end of the flight.
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Old 7th Apr 2011, 11:15
  #3131 (permalink)  
 
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Quote from Machinbird:
Some of you may also be surprised to learn that the A320 aircraft has encountered lateral PIO on a line flight.

Not uncommon, in my line-checking experience, due to what I have referred to (on another thread) as "sidestick abuse".
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Old 7th Apr 2011, 11:24
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Originally Posted by BOAC
whether inertia would have been sufficient to force it through the distorted doors and the uplocks is for physicists/engineers to say.
That it would do that is not in dispute, nor that the extended gear would separate at high enough forward speed. (Some "deep stall" or "flat spin" adepts postulate near-zero forward speed). What I find difficult to believe is that, if the gear was separated from the wing in more or less retracted position, taking large parts of its support structure with it, that it would end up in fully extended position relative to its support structure. Wouldn't the longitudinal 9g forces referred to by CliveL hinder its 'gravity extension'?

Regards,
HN39

Last edited by HazelNuts39; 7th Apr 2011 at 12:27. Reason: added text in italics
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Old 7th Apr 2011, 11:30
  #3133 (permalink)  
 
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if this strukture was part of the fuselage, then we mayby have a look of the middle seats, row 4 to 7
grity
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Old 7th Apr 2011, 12:22
  #3134 (permalink)  
 
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MLG pushed up or down

I guess in case of a retracted gear, it would depend on the A/Cs attitude during impact if upward or downward forces on the gear prevailed: the inertia forcing the gear down or the water pushing the main door an the gear up. The main door of the MLG would be one of the first parts of the A/C to hit the water.
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Old 7th Apr 2011, 12:23
  #3135 (permalink)  
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HN - I do not see it so clearly - the water, which is providing the retardation force is 'retarding' the gear also and may balance the 'inertia' of that. Only if you slowed the rest of the a/c leaving the gear unaffected by entry into the water would what you say be a 'definite'. I am sure the only certain way to know is to look at the various bits of the assembly in terms of what goes where on a 'normal' extension and what has sheared from what in line with CliveL's post. We could well just be looking a slow 'gravity' drop from a broken airframe as it made its way down 3900m.
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Old 7th Apr 2011, 12:29
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Regarding lack of occupant preparation...

mm43...



There are some indicators that will help, e.g.
  1. Those bodies recovered were probably not strapped in at the onset of the upset.
  2. Some abnormal 'g' forces were experienced throughout the upset period.
  3. A major pitch up in heavy turbulence could have resulted in a rapid negative CG shift - unbelted cabin crew and pax thrown toward the rear of the cabin.
  4. Any ensuing spin/rotation would have introduced forces that prevented cabin crew and pax returning to their seats.
If it were primarily a deep stall with not much rotation, I would expect the 'g' forces to actually be fractionally less than 1g for most occupants.

I tend to think there was 'total suprise and shock' in the cockpit of loss of control (on top of loss of everything else that had already happened). Furthermore there was some understanding that the situation was priority#1, absolutely all effort must be applied to deal with it as quickly as possible, everything and anything else was totally moot until it was resolved.

tt
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Old 7th Apr 2011, 12:40
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a quick off-topic

CONF iture, what about building 7? The NIST team has studied WTC7 quite thoroughly, and the study only confirms that the 9/11 conspiracy nuts are just that conspiracy nuts.

[end of off-topic]
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Old 7th Apr 2011, 12:43
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ttcse, the data from Pulkovo 612 confirm your expectations the RPM were too low to produce any noticeable Gs.
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Old 7th Apr 2011, 12:55
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Quote from BOAC:
HN - I do not see it so clearly - the water, which is providing the retardation force is 'retarding' the gear also and may balance the 'inertia' of that. Only if you slowed the rest of the a/c leaving the gear unaffected by entry into the water would what you say be a 'definite'.

I wonder if you may be missing the point, BOAC, re the inertia of the heavy MLG; in particular the bogie/wheel-truck part (furthest from the pivot point). At the extreme VS thought likely, the deceleration of the belly, or centre-section, as it struck the water would be great, due to its large surface area and relatively low mass. The bogie has a high mass and small surface area, relatively speaking. The door underneath it is light and flimsy.

Chris
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Old 7th Apr 2011, 13:18
  #3140 (permalink)  
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Machinbird,

I happen to be intimately familiar with a number of PIO incidents on A3XX aircraft, and there are two factors that have been most important in these:

1. The A3XX sidestick (control) philosophy is not rate but attitude based, i.e. you move the sidestick to the side (and with it a caret on the PFD), and the bus will keep the attitude you demand by pointing that caret. So, for example, you move the caret in the right hand side of the PFD and the bus will maintain an attitude to follow that caret. Unlike an analog system, where you bank the airplane and it will maintain most of the bank on its own while you just keep the bank angle with what's essentially neutral controls.

2. When in direct law (i.e. the proverbial has hit the fan and you're one failure short of MAN PITCH TRIM ONLY), it'll start behaving like an airplane you learnt to fly on... and you're in effect flying a rate based control system, where your inputs have to be given differently.

While I have great respect for the beautiful autoflight systems airbus has developed, this very basic control philosophy is flawed in my opinion and could have been part of what unfolded in the middle of the night over the atlantic, inside a CB. Don't go there. We teach that at basic levels...
 

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