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AF447 Thread No. 3

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AF447 Thread No. 3

Old 1st Jun 2011, 23:47
  #1061 (permalink)  
 
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Hi takata,

sorry for the late reply
As it seems that we are in agreement about where was seated the relief pilot, I would like to understand what makes you to believe that the RP was FO1 (4400 hrs)?
I think we agree but just to make sure: I think the RP was the pilot who was qualified to be in the L/H seat during the cruise part of the flight. We would need somebody of AF to clear this but as of to date I am thinking that a relief F/O takes the LH seat. A relief captain could take the RHS as well but this was not the case.
A pilot with 800 hrs does not have this LH seat qualification, so he was in the RHS and in this case, also PF.

Edit: see PJ2 answer to Lemurian, they both agree to the opposite:
Quote:
Originally Posted by PJ2
Quote:
Originally Posted by Lemurian
- In all certainty, the operation of this flight was performed by a senior F/O seating on the RHS with command functions and a junior F/O seating on the LHS with basic radio-com and navigation duties, along with some minor engineering duties.

Agree.
Sorry, I missed this part of Lemurian's post, but yes: I do not agree with that. The senior F/O needs to be in the LHseat. (I can hear future discussions already, where we will be told that a 3crew cockpit need to consist of at least two captains.)


@paull
I suppose some people are hoping to say, 'an inexperienced pilot made a mistake', so we can all sleep easy. Very tidy, sorry I don't buy it.
I am not hoping to say anything. I am talking about facts. Fact is: PF had 800hrs experience on type. There were two other pilots with more experience on the flight deck. Would that help to improve the overall situation? DEFINITELY
Would it help if somebody of the more experienced pilots flew the aircraft?
I DONT KNOW
I feel more comfortable with some 10k+ hrs on 320/330 today as I was feeling with 800hrs. No grading, no qualification argument, just another fact.

Regards
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Old 2nd Jun 2011, 00:03
  #1062 (permalink)  
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What is highspeed stall ?

I'm sure that your question was tongue in cheek at the time.

However, for the discussion, at least two situations might be so described -

(a) a pitch up to an appropriate G-level can cause an accelerated stall. In effect, the wing sees a "heavier" aircraft due to the load factor and stalls at the higher speed. Handling characteristics may be considerably more interesting than for the normal certification stall.

(b) at very high pitch rates (as I recall from an RAeS report on the subject - in excess of something like 70 deg/sec) a quasi-stable upper surface vortex (a bit similar to the stall vortex on a delta) can see the stall angle pushed considerably higher than what we see for the normal certification stall. Generally not relevant to most fixed wing aircraft but, apparently, a problem in the rotary wing arena at times.
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Old 2nd Jun 2011, 00:31
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High speed stall amd mach

Great points, JT the Moderator.

It could be that the term bandied about refers to mach effects such as I related from the Yeager discussion.

If we exceed the "critical" mach, we can see things like aileron reversal, nose tuck, flutter, etc. All these bad things due to the shock wave moving back along the stabilizer or main wing and preventing the normal control surfaces at the rear of the wing or stabilizer from acting normally.

Another way to get into trouble near the critical mach is to rapidly change your AoA. The shock wave will move along the chord of the wing and have the same results as exceeding the critical mach. This more closely resembles the "high speed stall" phenomena described by JT the Mod.

Unless you are driving a supersonic design, pulling back the power is usually sufficient, as you are already experiencing a lotta drag. If in a dive, that may not be enough and spoilers or other drag devices might also be required. As most airliners have swept wings, they are more tolerant of mach effects than the old straight wings, so I am not too worried about mach-induced control problems for the present scenario we are discussing/analyzing.
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Old 2nd Jun 2011, 00:35
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AF 447.No connection in reality , but.............!!

I recently thought to try FSX simulator software (AB320) to see what would happen if I selected fully nose up trim and nose up elevator at cruise and reduced power to idle when reaching the top of climb. IAS starting was 250 kn. Autopilot OFF.

The AB320 climbed from 19000 @ 250 kn IAS to close to 37000 feet at around 38 degr nose up and went into a deep stall whilst starting rotating and changing bank angle. The height achieved is questionable, in my opinion even though full power was used to the top of climb..

Putting the trim fully forward (in clean configuration) produced no effect as well as nose down elevator. The aircraft remained doing scary gyrations around all axis.
Putting the gear down and flaps down produced no result with the trim at fully nose down and power at idle.

Putting the trim neutral and adding full power and nose up elevator caused the aircraft to leave the stall and dive to gain (excess) airspeed.

Again; this is (very limited) MS FSX at work and all I am trying to bring to the forefront is
whether there could have been a situation where "the book should have been thrown out the widow"? I seem to recall several instances where pilots did this and got out of desparate situations !

Although it is theorizing, what are your professional thoughts on this?
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Old 2nd Jun 2011, 00:57
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I'm familiar with mach buffet which I guess some people call high speed stall. It isn't a stall but supersonic flow over the wing when you are high and too fast. Low speed buffet at high altitude is when you get supersonic flow over the wing because of high AOA and the increased airflow over the wing. Flying the big jets explains it very well if anybody is interested. The book explains a lot that most instructors don't know. Things like why the IAS for stall increases with altitude. Never found the answer to that anywhere else.
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Old 2nd Jun 2011, 01:12
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Food for thought. Is there any connection with the FL increasing 7000f/m, then FL-10000 f/m, and Tim Vasquez's revised Met analysis?

i personally do not think there is a direct connection. for me it seems that the initial massive climb at this altitude resulted from pilot action pulling back the stick and using aircraft energy ( FL 350 and M 0.8 should result roughly in 270-280 KIAS) for this climb until the plane ran out of airspeed and stalled. the -10000 f/m are simply a more or less ballistic fall down with stalled wings.

two more things which here are discussed

1) a deep stall ( where the tail is in the shadow of the stalled wings and you have no elevator effect) should affect t-tail planes and the a 330 is another design. further it seems from the interim report that the pilot held the stick back most the time until impact so serious attempts for a recovery were not made.

2)the pitch up moment from applying TOGA. well, at FL350 the turbines are far away from developing the same thrust like at sealevel and so i doubt that pulling the levers forward from the CL notch gave here an significant additional pitch moment , especially that before this the engines were not idling but in cruise power.

best regards !
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Old 2nd Jun 2011, 01:16
  #1067 (permalink)  
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bubbers44;
I'm familiar with mach buffet which I guess some people call high speed stall.
So...as per comments above and your experience, can the difference between Mach buffet, and stall buffet, be felt/determined? Your thoughts...would one know when one is in high speed or low speed buffet?

I've felt high speed once, very briefly, and it was "sharp". I haven't felt low speed, at high altitude except in the sim and I don't think the sim experience, (Level D sim) is valid beyond "normal".
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Old 2nd Jun 2011, 01:17
  #1068 (permalink)  
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mach buffet which I guess some people call high speed stall

No really. What gums is talking about occurs somewhat about the onset of initial buffet. Not a stall, per se, but does involve flow separation and certainly can result in an upset - similar result for the pilot, I guess.

Low speed buffet at high altitude is when you get supersonic flow over the wing

You might like to go back and re-read up on this one ? Lowspeed buffet is normal prestall buffet. Highspeed buffet is the onset of shock wave related flow problems. Mind you, at normal cruise levels, the two might not be separated by a large range on the airspeed side of things.

Things like why the IAS for stall increases with altitude. Never found the answer to that anywhere else.

One should find this in most of the basic books covering aerodynamics
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Old 2nd Jun 2011, 01:24
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well, beyond the fact that a laminar flow wing may stall with little or no buffeting i doubt anybody can answer how a mach buffeting and low speed buffeting feels in an a330 since on the one hand in normal law the airplane ( as well your company ) does not allow such situations and on another hand every pilot tries to keep away from this. i think we can agree that stalling a widebody is a very serious situation and something other than a cessna 150. surely the pilot of af 447 had other problems than feeling into mach or low speed stall buffets.
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Old 2nd Jun 2011, 01:26
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Stability

Didn't I read on these pages that the AB get away with relaxed stability, whatever that means, rather than positive stability, due to advanced stall protections?

Brain starting to smoke - gotta' go.
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Old 2nd Jun 2011, 01:31
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Rockhound, do be aware that the BEA's job is to diagnose what went wrong and recommend any required changes in procedures or hardware to make flying even safer. They are not chartered to find blame. So remaining ambiguous avoids the blame game.Personally I think that was quite wise of them. (Compared to when I was a child air safety is outrageously unbelievably good. But, nothing is 100% even though that is a laudable goal towards which one should strive.)
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Old 2nd Jun 2011, 01:53
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"in two minutes we should enter an area where itíll move about a bit more than at the moment, you should watch out" and he added "Iíll call you back as soon as weíre out of it".

They were clearly expecting some "buffeting", so isn't it likely that any stall buffeting they felt, when combined with a "what's it doing now" a/c that seemed to be seriously misbehaving, would have been missed, or misinterpreted?

I was once the best damned VW Beetle mechanic I knew... but then I got one that was fuel injected and it had a computer, and lots of sensors.... whenever anything went wrong with that thing I almost always thought it was the computer fouling things up... and it rarely was.... I was almost useless with that machine.

...point being, I think it's entirely possible that the PF was under the illusion that, since his airspeed was u/s, and other things didn't seem to add up -- how come when I pull back on the stick I don't feel my body being shoved into the seat? -- the PF said "I donít have any more indications", and the PNF said "we have no valid indications"..... the "what's it doing now" airplane must be badly fouled...

Given the 30 seconds of aft, left stick he'd held at one point, it would certainly seem he must have been acutely aware of some kind of an apparent disconnect between his actions and the ship's response.
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Old 2nd Jun 2011, 02:18
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Why all the Nose Up Stick on AF447??A Theory

This is a possible explanation of the AF447 pitch up from FL350 to FL380. This is theory or speculation at this point. I believe the pitch up was inadvertent, was caused by difficulty in managing roll angle which task overloaded the PF to the extent his scan broke down.

Before you exclaim "Poppycock" or BS or whatever, let me set the probable reasons and scenario.

First, lateral control in the bus would normally be done with the fingertips and with small motions of short duration. The normal roll rate depends on deflection from stick centered for both Normal law and Alt 1 Law. Normal law would command a rate of 15 degrees/ sec with full deflection and Alt 1 is "similar to normal law" except you lose spiral stability.

When you get to Alternate 2 law, things are quite different in the lateral axis. Control surface deflection is directly proportional to control deflection-period. No turn coordination with the rudder. No roll limits, you can roll without the bus fighting you. If the aircraft is in balanced flight at this point, no big deal. Probably just a little bit more twitchy than you are used to. Maximum roll rate is now 20 to 25 degrees per second depending on speed and configuration.

The problem comes when you are not in balanced flight. Suppose the rudder changes its trim point in the switch to Yaw alternate law (this may be a function of rigging of the control system.) The effect of this is that your lateral zero roll position now changes to a point not in the center of the lateral travel, and you have to exert force to hold it there.

How much force?
For the A320 from a 2004 post by 'Max Angle'
Quote:
The figures copied from an Airbus publication and converted from horrid Euro units to pounds are:

Breakout force: 1.1 pounds

Pitch: Fore and aft. +/- 16 degrees 22.5 pounds

Roll: Outboard 20 degrees 5.6 pounds.

Roll: Inboard 20 degrees 7.8 pounds.

Note that the force is different for inboard and outboard roll. Airbus found during development that your arm is stronger moving inboard than outboard and fine tuned the forces to make left and right roll feel the same. Try moving the stick left and right holding it from above next time you are at work, you can clearly feel the force difference.
I have to imagine that the A330 stick is almost identical. They do want an easy transition from one aircraft to the other after all.

What does this mean to lateral control? It suddenly becomes very difficult. Yes 7.8 pounds isn't that much force, you can hold that with one finger-for a while.

But you are flying an aircraft yourself now on the lateral channel. You are fighting transitions across the breakout force point and experiencing reversing stick forces. It is sort of like a cruel instructor trying to make your life very difficult by riding the controls and applying spurious inputs. It is impossible to fly the aircraft smoothly with this type of control interference. The best you can do is get a firm grip on the stick and balance your own muscles against each other so that the interfering forces are small in comparison to your own applied forces.

Problem. How do you keep from making inadvertent pitch inputs in this situation. Answer, you probably can't until you can release your grip on the stick back to more conventional levels.

"Oh that is easy", say you. Just move the rudder trim in the right direction and the plane will straighten up and fly right.
Problem. The PF has a serious roll control problem and a host of other distractions. He doesn't have the free brain cells to realize that his wing problem is correctable by the rudder, a different control surface. That takes a moment of calm insight which was not available. Remember, he's an Airbus guy. He flies with his feet on the floor to keep from accidentally kicking the tail around. His aircraft normally keeps everything in trim for him. He has never experience anything like this, particularly not at night, with a major pin ball show going on in front of him, at 2 in the morning.

Look at the BEA initial data report.
The initial roll was to the right. (There is your heavy wing.) And the PF made a left nose up control input. I wouldn't be surprised if his thumb was pointed up along the stick He probably was curling his wrist to control the wings. Mama Airbus is keeping the nose more or less where it belongs for now so I'm going to concentrate on getting these wings under control for now. If this thing rolls over, we are going to be doing a split S! Can't let that happen.

I wouldn't be at all surprised that we find that the majority of his control inputs were to the left and that he was accidentally pulling the nose up at the same time.
I'll bet that they find dents in the floor beneath the R seat rudder pedals, in a location indicating that his feet were still on the floor at impact.

Remember-whichever guy was PF, he was in the right seat and was therefore flying with his right hand The limited data made available seems to show that the rudder trim was never set. Whenever there is a description of the aircraft's roll behavior, it is oscillating.
Of course, once you get into a stall range, wing rock is a common result.

OK, I still have some work to do. Have a chew on this. There is more later if necessary.

Suggested area for discussion is, "What was the PNF doing all this while?"

Last edited by Machinbird; 2nd Jun 2011 at 02:30.
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Old 2nd Jun 2011, 02:43
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Back to basics

Things like why the IAS for stall increases with altitude. Never found the answer to that anywhere else. ????

Come on guys, back to basics.

Thats because the airspeed does increase. Less density means less lift, so more speed is required to produce the same amount of lift.
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Old 2nd Jun 2011, 03:09
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Thats because the airspeed does increase. Less density means less lift, so more speed is required to produce the same amount of lift.
That'd be the TAS that increases, BB.
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Old 2nd Jun 2011, 03:22
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Machinbird
He doesn't have the free brain cells to realize that his wing problem is correctable by the rudder, a different control surface.
Good post. I've got an impression that there will have been a very disturbed airflow over the rudder, and with the AoA and the existing RTLU limitations, the +/-7.9į available may not be effective. We certainly don't know if the rudder was used, but if it was, the BEA must have seen nothing significant in its use, not to mention it.
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Old 2nd Jun 2011, 03:41
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Control inputs and stability

@Gray

We went thru this ( relaxed static stability and c.g. and....), and even posted charts and graphs and testimonials. I had to back off of some thoughts once some of the 'bus manuals were placed here for consideration. The 'bus is not nearly so "twitchy" as the jet I flew due to the c.g., and the company's goal of reducing drag due to down force by the rear stabs in cruise flight seems O.K. as long as you are FBW versus conventional flight control systems. I only brought up a discussion of the concept due to my own experience with "relaxed static stability" and the potential to reach a flight condition that is difficult to deal with.

There are several things about the 'bus flight control law implementation I do not like, but the basic concepts of the jet seem fair.

and for the 'bird observations:

- It is true that we tend to put in aft or forward stick when rolling right or left. Seems that some FBW systems with the small "side stick" are even canted to account for this. OTOH, I don't see this as a big deal for this accident.

- As 'bird has noted, rudder trim is available, but I can't find a note in the manual about the system "trimming" the rudder for zero yaw in the stable flight condition - no aileron input or pitch input, just flying st and level. With the laws that the jet uses, about the only thing I can see the rudder pedals for is nosewheel steering or countering roll when in a stall or close to a stall. This is due to basic swept wing aero.

- There is no roll trim on the beast, best I can determine reading all the manuals. This is unlike the FBW jet I flew, where roll command was identical in concept to the 'bus, but we carried ordnance and could have asymmetric loads that were a significant part of our gross weight. Our roll rate command was a bit more in magnitude, think max was about 280 deg per second at 16 or 17 pounds of pressure. Our trim max command was less than 280 deg/sec, hence, when my LEF folded up I had to hold constant pressure for about 15 minutes until getting back on the ground. Also had to trim rudder a bit.

- The pitch trim mechanization on the 'bus is gonna be a player in the final findings, and I'll place my bet now.

Why is that, Gums?

It's because you can't manually trim for a desired gee or attitude or AoA , even using the THS manual wheel. If you constantly hold even a slight bit of back pressure, the THS moves to help maintain your existing gee command and the elevators do the "fine" work. Need a 'bus driver to try this out in flight - jez kidding! Let go of the stick in Normal or Alt and the sucker re-trims the THS for a 1 gee baseline ( corrected for pitch attitude and bank angle, both to specified limits).

So my feeling is the constant back stick moved the THS to almost max, then got stuck there in Abnormal mode or was maintained there in Alt mode due to constant back stick gee command. No AoA limiter as we had in the Viper. In that sucker we hit 9 gees at 15 deg AoA and then if we continued to demand max pitch the gee command would be reduced to 1 gee at 25 deg AoA, even if we pulled 100 pounds on the stick. Our AoA limiter worked very well except at a combination of extremely high pitch attitudes and very slow speeds and little or no roll rate.

Gear down we added an increased AoA bias to the basic gee command, plus we increased pitch rate feedback. The result was a fair simulation of "normal" jet approach characteristics, in that we could trim for an airspeed/AoA versus a pure gee.

Finally, the THS can't help but be the primary driver at the edges of the envelope, and the elevators act like "trim tabs". It acts like the "all-moving" stabilizers you see on all the jet fighters.
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Old 2nd Jun 2011, 04:19
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- It is true that we tend to put in aft or forward stick when rolling right or left. Seems that some FBW systems with the small "side stick" are even canted to account for this. OTOH, I don't see this as a big deal for this accident.
Hey Gums,
When your Leading Edge Flap (LEF) on your Viper folded up and you were flying with nearly full lateral stick, did that give you control problems other than banging into the control stop on one side?

I don't imagine you ever needed to go through the center of the lateral stick travel then. Would that have made life more interesting with the force reversals on the stick? (Never mind, your Viper stick didn't move, did it?)

Supposing your aircraft wasn't computer stabilized in roll any more and was oscillating quite a bit in roll. How much pucker factor would that have added?

Just trying to put Viper experience in a comparable context.
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Old 2nd Jun 2011, 07:16
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High speed and low speed buffet

Originally Posted by PJ2
So...as per comments above and your experience, can the difference between Mach buffet, and stall buffet, be felt/determined? Your thoughts...would one know when one is in high speed or low speed buffet?
As explained in the previous thread, I don't think there is significant difference between high speed or low speed Mach buffet. Perhaps the frequency changes gradually with Mach number, and that may be noticeable if there is a large spread between the high and the low limit. But since an airline pilot never gets there, would he be able to recognize the difference?

Last edited by HazelNuts39; 2nd Jun 2011 at 07:30.
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Old 2nd Jun 2011, 07:28
  #1080 (permalink)  
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Originally Posted by macinbird
Suggested area for discussion is, "What was the PNF doing all this while?"
- we both agree here - it really is less significant who was in which seat, since both pilots were line-qualified. What IS significant, as I have said a few times (it really is crucial and we are not being told!) is what PNF said during this amazing and frightening zoom climb. Until we know that we cannot progress, I feel.

How many of us would sit 'quietly' in this scenario? Was it a mutually agreed manoeuvre? If not, were 'challenges' issued? If it was agreed, why? There, surely, will lie the clues as to what PF was 'seeing'? Any 'leaks'?

To pick up on those questioning the absence of a 'Stall' warning at low IAS - I'm pretty sure that had this been not blocked, there would be a fair chance that they might have recovered and not sensed the need to 'reverse the last input' when it sounded again during recovery. It appears that because the designers were convinced this situation could not develop due to the 'protections' that they didn't bother?
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