Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

AF447 Thread No. 3

Tech Log The very best in practical technical discussion on the web

AF447 Thread No. 3

Old 9th Jun 2011, 21:24
  #1701 (permalink)  
BarbiesBoyfriend
Guest
 
Posts: n/a
bearfoil

sadly, you are correct I think. IMHO this accident will go down, correctly, to that much malgned term 'pilot error'.

I've been in a MoFo CB and it's not pretty. But hey, although my instruments werre working, I couldn't read them!

Sitting here, my brane 'says, pole the plane on its attitude and leave the throttles alone'- suck it up!

WTF would you climb? Fear?
 
Old 9th Jun 2011, 21:32
  #1702 (permalink)  
 
Join Date: Feb 2008
Location: In the Old Folks' Home
Posts: 420
Received 2 Likes on 1 Post
Caution About AoA Indexer

Glad Rag, again, I need to caution everyone here who has not routinely flown AoA, AoA indications at approach speeds assist in quite precise pitch control, but not at cruise speeds because AoA changes very little with airspeed at the higher speeds. It's a bit like balancing on a bowling ball. It's possible but not easy.

LW50: Yes, the indexer ordinarily is activated only with the gear down, but that could be changed, of course. On the other hand, the typical AoA indicator would certainly give the pilot an indication of AoA which was near stall.

Would I like to see an AoA indicator installed and used in transport aircraft? YES! Proper use of an AoA indicator might have prevented this accident. Of course, so could some other things.
Smilin_Ed is offline  
Old 9th Jun 2011, 21:36
  #1703 (permalink)  
PJ2
 
Join Date: Mar 2003
Location: BC
Age: 76
Posts: 2,486
Received 2 Likes on 2 Posts
Originally Posted by gums #1698
With unreliable airspeed (think impact pressure, dynamic pressure, CAS/IAS), I look at some of the alternate laws and still see clues that the confusers are trimming the THS. So without airspeed, the jet is still trimming to maintain one gee. It does not care about the pilot aft stick input other than to keep the stick deflection about the same angle regardless of speed. How does it do this? It uses the accelerometers that are the major players for the basic control concept of a gee command versus an AoA command system. You don't need airspeed for the accelerometers to work. Same for body rates. Saw this on one of our accidents when a pelican wiped out pitot tubes, hemispherical air data gizmo and AoA vanes.

So a constant, even a small aft stick, that is commanding maybe 1.1 gee could result in the confusers increasing the THS angle to maintain the same stick angle for the commanded gee. No air data required. This might explain the THS increasing angle.
Concur.

The C* Law in the A320/A330/A340 is gee driven. Alternate Law 1/2 are variations/protections bolted onto the C* Law. In Direct Law, the stick is a B737 control column and its WYSIWIG including trim.
Lonewolf_50;
f you don't train for a stall recovery on instruments (for reasons previously explained, to include sims that can't replicate it), what does a pilot finding himself in a stall have in his training background and experience to draw on in order to redirect his scan.
I think this is one thing that is going to come out of this accident - proper stall recognition and training and not mere entry-and-recovery (where minimal loss of altitude has been not only stressed but is an actual IFR-ride failure if more than nnn feet are lost in the recovery!! - clearly designed for low-altitude stalls, (and even that didn't work for THY).

To do this, both simulators and curriculae have to change and that is a very tall order given the comments on sim performance beyond loss of control regimes.

Given the past ten years' data on stall accidents however, the industry is showing that it needs to do something. Along the way, the discussion about automation and the man-machine interface will take place in earnest just like we wanted it to when we checked out on the A320 in 1992.
PJ2 is offline  
Old 9th Jun 2011, 21:39
  #1704 (permalink)  
PJ2
 
Join Date: Mar 2003
Location: BC
Age: 76
Posts: 2,486
Received 2 Likes on 2 Posts
Smilin'....
It's a bit like balancing on a bowling ball.
Because the L/D curve is as shallow as a dinner plate and one is trying to keep a marble in the middle... ;-) !
PJ2 is offline  
Old 9th Jun 2011, 21:52
  #1705 (permalink)  
 
Join Date: Aug 2007
Location: London, New York, Paris, Moscow.
Posts: 3,632
Likes: 0
Received 0 Likes on 0 Posts
Smilin_Ed,PJ2

Cheers guys just a shot across the bows so to speak.
glad rag is offline  
Old 9th Jun 2011, 22:00
  #1706 (permalink)  
 
Join Date: Jun 2009
Location: I am where I am and that's all where I am.
Posts: 660
Likes: 0
Received 0 Likes on 0 Posts
PJ2 made a comment I hoped to elicit, "DO NOTHING was the correct response and that is the action which would have "prevented" the loss of control."

I also note that something like this had happened before to a fair number of planes that sailed through it with fine aplomb.

What might have been different with AF447 other than a different cast of characters? In my mind I don't picture pilots acting on whim or instant panic. (And the BEA highly edited release seems to indicate rationality all the way down.) Was there something the other planes had which saved them, like a bright Moon or another extra form of reference that reassured them? Or was something missing with AF447? Or did training simply break down?

(I seem to remember talk here about those rules being standard at the time of this accident. Wasn't some aspect of it changed to "always believe a stall warning?" Has a future problem been setup?)

As a note his roll input doesn't bother me. A strong enough pull on the stick to cause the plane to zoom 2000' like a marble rolled on the tabletop towards an incline (up and slower is the result) bothers me. So please let me ask, "if the controls really are sensitive enough that the "natural" bend of the wrist to correct a roll would also induce a climb?" I believe somebody remarked taht the sticks are mounted at a modest angle to vertical to accommodate human the restraints of the human skeleton. So that supposition of accidental input seems wrong. So I reask, "What made the PF decide he needed to climb? Might it be to avoid something and he forgot throttle was frozen? Might it be he thought there was an over speed condition and he needed to slow down immediately?"

Your UAS list comment is one we should enter formally into the record and discuss. It does appear to at least partially answer the above. 2000', however, seems to cost a tremendous amount of speed. I'd think 500' or 1000' would be about the limit of what you'd want to lose in a pull up action.

If this series of inputs and reactions still does not make any sense let's put a "post it flag" on that time and look at the other intervals in the release. I'm looking for actions or even stimuli that could be modified slightly to have eliminated or recovered from the bad situation that led to the crash.
JD-EE is offline  
Old 9th Jun 2011, 22:10
  #1707 (permalink)  
BarbiesBoyfriend
Guest
 
Posts: n/a
JD-EE 'Rules' are always valuable.

But they should never replace what your instructor taught you on your PPL.
 
Old 9th Jun 2011, 22:15
  #1708 (permalink)  
 
Join Date: May 2011
Location: NEW YORK
Posts: 1,352
Likes: 0
Received 1 Like on 1 Post
While this is surely true in retrospect, it seems contrary to most training.
The pilot assumed control as the airplane banked.

How does he know that the bank is self limiting?
Is not the drill to level the wings?
etudiant is offline  
Old 9th Jun 2011, 22:28
  #1709 (permalink)  
 
Join Date: Oct 2009
Location: UK
Posts: 1,270
Likes: 0
Received 0 Likes on 0 Posts
Hi etudiant,
How does he know that the bank is self limiting?
It's not self limiting.

"LATERAL CONTROL
When the aircraft flying in pitch alternate law, lateral control follows the roll direct law associated with yaw alternate or mechanical.
ROLL DIRECT LAW
BANK ANGLE PROTECTION
Not provided."
rudderrudderrat is offline  
Old 9th Jun 2011, 22:31
  #1710 (permalink)  
 
Join Date: Jun 2009
Location: florida
Age: 81
Posts: 1,617
Received 68 Likes on 23 Posts
Shallow L/D curve and AoA and speed

Well put, Smilin' and PJ. OTOH, I wouldn't call it like balancing a marble on a dinner plate.

The Airbus manuals have a diagram depicting "stall protection", and that graphic looks like that of a Cessna. Trust me ( and Smilin'), the graphic does not show the relatively gentle curve that most all swept wing planes have. Those suckers do not have a sharp "break", then a stall. They tend to buffet a lot, maybe have some roll oscillations, and finally fall off on a wing or "mush". If the jet has super directional stability, it may stay fairly wings level and not yaw too much. Look at the F-18 demo's and think about the jet's AoA and how easily it passes the reviewing stand without a lotta wing rock or yaw.

The other thing is that the curve is also fairly gentle with respect to IAS/CAS. So 10 or 20 or 30 knots is no big deal.

Doubt if anyone here flew a delta or the Concorde, but who knows. My limited time in the F-102 was "educational"( 80 hours or so). No real stall you could see or feel. Thing just descended with the VVI pegged at 10,000 feet per minute. Mild buffet, more of a buzz. Viper was about the same due to the variable camber courtesy of the leading edge flaps.

later, and I shall try to have some of those archaic FBW control diagrams in a great format for history.
gums is offline  
Old 9th Jun 2011, 22:36
  #1711 (permalink)  
 
Join Date: Nov 2006
Location: SoCalif
Posts: 896
Likes: 0
Received 0 Likes on 0 Posts
Symphony of Flight

Pardon if this comparison is lacking; my musical skill is limited to playing the radio.

An airliner on departure, climb, cruise, descent, approach and landing is like a symphony orchestra, with all the components working in concert.

The conductor can be the FMS, Flight Management System, or the aircraft commander.

It's all seamless and symphonic until a component hits a sour note. Then you really see the contribution of the other components and what is driving them.

It's basic to conventional airplane dynamics, as taught in Langewiesche's "Stick and Rudder" and hundreds of other instructional manuals:

Pitch controls airspeed.
Power controls altitude.

The A330 Flight test accident in 1994 uncovered the flaw in Airbus logic. The plane was on autopilot in Altitude Capture mode when the pilot pulled the power on one engine. The AP responded to lack of power by pulling the pitch up to over 30 degrees. Instead, it should have kept the pitch at desired speed, and told the pilot, "We can't do that."

The TK951 B737 approach accident at AMS in 2007 revealed the same flaw. An undetected erroneous input to the A/T caused it to go to Flight Idle. The autopilot tried to stay on Glideslope by pulling the nose up and trimming to lower speed to make up for lack of power. Instead, it should have kept the desired speed, and let the plane sink below glidepath. If the pilot hadn't caught that, he would have heard, "TOO LOW! GLIDESLOPE."

Firewalling the throttles would have stopped the sink, and not have caused such a pitchup, as the elevator would still have been trimmed for the correct speed. The pilot could have intentionally traded some airspeed for altitude, and without fighting full aft trim.

How does this apply to 447? We'll see. Trying to control altitude with pitch is a loser, regardless.
Graybeard is offline  
Old 9th Jun 2011, 22:36
  #1712 (permalink)  
 
Join Date: Jun 2009
Location: I am where I am and that's all where I am.
Posts: 660
Likes: 0
Received 0 Likes on 0 Posts
Bearfoil, is it a total blunder if you have a UAS condition to apply UAS procedures? Did he pull the stick before the stall warning or after? It appears to be "before" in the rude imprecise chronology of the released data.

And simply for my own information I have some related questions.

* If he should have waited to apply UAS procedures then how long should he have waited?

* What is the intended purpose of the UAS procedure. It seems to be to slow down the plane to get it into a safer margins condition between stall and overspeed, which was already happening.

* Might the pilot have asserted the "slow me down quickly" planning to lose maybe 50 knots by climbing 500' to 1000' and then level off only to have the stall warning derail his thought processes?

* Is everyone happy with the UAS scenario PJ2 suggests. It seems to partially fit to my untutored eyes. If it was not UAS, why was it not? If it was not UAS, then what the heck else might the pilot have been doing presuming he is rational with no deathwish? Too many here are willing to accept conflicting data in such a manner as to suggest the pilot simply messed up. I'm ornery. WHY might he have messed up? Absent a good reason I'm not willing to give the "pilot messed up" crowd an ear, including the French Transport Minister.

We need i dots and t crosses applied to the appropriate letters here.
JD-EE is offline  
Old 9th Jun 2011, 22:37
  #1713 (permalink)  
BarbiesBoyfriend
Guest
 
Posts: n/a
The trouble with the scarebus is, when the autos roll over, what you're left with is a Boeing.

And as you are a scarebus pilot, you don't know how to fly a boeing.
 
Old 9th Jun 2011, 22:54
  #1714 (permalink)  
 
Join Date: Jun 2009
Location: I am where I am and that's all where I am.
Posts: 660
Likes: 0
Received 0 Likes on 0 Posts
Gums, I was starting to read PJ2's posting with its quote from your 1698 when a coin dropped in my mind.

I got this far, "So a constant, even a small aft stick, that is commanding maybe 1.1 gee...."

1.1 G according to which measurement facility, inertial, measured stresses on airframe, or what else? I just want to get on the same page as you since this is important.

Also important is your remark about vocabulary. The words "protections" and "limits" are seen quite differently by most people. The former gives a sense of safety and the latter gives a sense of urgency.
JD-EE is offline  
Old 9th Jun 2011, 23:25
  #1715 (permalink)  
 
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 82
Posts: 1,454
Likes: 0
Received 0 Likes on 0 Posts
JD-EE
PJ2 made a comment I hoped to elicit, "DO NOTHING was the correct response and that is the action which would have "prevented" the loss of control."
I'm not sure Do Nothing was a valid course of action either. As I understand it, there is nothing automatic to keep the machine right side up in roll while in Alt2 Law. The pilot has to fly the wing roll attitude.

If it was in lateral trim, probably no big deal to fly it in roll direct law, just be gentle but firm.

Out of lateral trim, it would be a complete handful-until you balanced it out with rudder trim.
Machinbird is offline  
Old 9th Jun 2011, 23:57
  #1716 (permalink)  
 
Join Date: Dec 2010
Location: Middle America
Age: 84
Posts: 1,167
Likes: 0
Received 0 Likes on 0 Posts
Thrust

PJ2,

In the most recent discussions regarding pilot actions, stall warnings, etc., the one thing that isn't mentioned much are thrust settings. Recall I had asked about the N1% differences between normal cruise at Mach 0.83 and reduced turbulence N1% for Mach 0.80. The questions I had behind this has to do with how this may have affected subsequent events. With a reduced N1% at cruise at 35K, for some reason (probably pitot tube blockage due to ice crystals), the AP/AT suddenly dropped out in a probable turbulent atmosphere. I am assuming when this happened, the engine thrust level remained at that for turbulence penetration, whether or not thrust lock occurred, as the pilot had prior reduced the thrust setting manually. If so, then the first input from the PF was to correct a roll situation while inputting a nose up command with the side stick. As the turbulence thrust setting was for level flight, would the aircraft given weight, COG and reduced speed be more vulnerable to a potential stall situation more rapidly? We know that speed was deteriorating rapidly after the nose up side stick command, but perhaps the pilots didn't know this. However, when the stall warning activated, my thoughts are that it was genuine, the aircraft was saying, "Keep doing what you are doing and we are going to stall". From what data has been released by the BEA, the throttle levers were never moved manually until such time later in the sequence when the throttles were moved to TOGA.

What are your thoughts on this?
Turbine D is offline  
Old 10th Jun 2011, 00:12
  #1717 (permalink)  
PJ2
 
Join Date: Mar 2003
Location: BC
Age: 76
Posts: 2,486
Received 2 Likes on 2 Posts
JD-EE;
PJ2 made a comment I hoped to elicit, "DO NOTHING was the correct response and that is the action which would have "prevented" the loss of control."
I made that comment shortly after the airspeed-ACARS discussion began in July, 2009 and have done so several times since to get that aspect of the discussion going. "Do nothing" not only makes complete sense to a pilot because the airplane was stable and doesn't need an airspeed indicator to fly, but doing something takes one into unknown territory because one is no longer at the original pitch and power setting and there are no breadcrumbs back and no airspeed. I later posited that the pull-up was in response to one of the memorized items in the UAS drill. Maybe, maybe not, but the airplane didn't pitch up all by itself.

So please let me ask, "if the controls really are sensitive enough that the "natural" bend of the wrist to correct a roll would also induce a climb?"
They can be, if one is ham-fisted but that applies to every transport I've flown. Yes, a climb can be induced accidentally, perhaps under stress or turbulence (discussed previously) but I know of no pilot, especially of this experience, who, after having unintentionally applying such movement, would permit the result to develop into what it did without stopping it. An immediate, tiny, gentle correction would be all that was needed to return the airplane to the cruise altitude, while correcting the roll. Hardly a change in 'g' would be needed.

The airplane hand-flies beautifully at cruise altitudes. As always with any transport aircraft, you have to be gentle with it, making tiny control inputs. It will respond aggressively if you make it by using a handful of stick movement. I would not expect that of someone with as much time on the airplane as the F/O had.

So I reask, "What made the PF decide he needed to climb? Might it be to avoid something and he forgot throttle was frozen? Might it be he thought there was an over speed condition and he needed to slow down immediately?"
Without the data we cannot say.
Your UAS list comment is one we should enter formally into the record and discuss. It does appear to at least partially answer the above. 2000', however, seems to cost a tremendous amount of speed. I'd think 500' or 1000' would be about the limit of what you'd want to lose in a pull up action.
Yes...so the question is, why did a pitch-up maneuver make sense? Did it have to? We cannot say without the data.

Since the BEA's note, we've all been at it, working overtime to fill in the frustrating holes and blanks, trying to make sense of something that does not lend itself easily to such a task and is difficult to come to terms with. This is a rational enterprise in a thoroughly rational industry so that is how we work it to answer the questions we are all so familiar with and talk about. The notion is discussable as one idea among many. The data's the thing and cranes, not skyhooks must do the heavy lifting where there is a disconnect in this or that theory. But I have yet to see an explanation involving the AFS which fits within the known facts about the aircraft and what we know happened, without the use of skyhooks.
PJ2 is offline  
Old 10th Jun 2011, 00:14
  #1718 (permalink)  
bearfoil
Guest
 
Posts: n/a
JD-EE

Bearfoil, is it a total blunder if you have a UAS condition to apply UAS procedures?


Let's turn that around. Why initiate UAS c/l if UAS has not been identified?
It is not until 2:10:16 that PNF notes "lost speeds" then "Alternate Law". The a/p is reported to have been lost at 2:10:05 ("I have controls"). From the release, the pilot is said to have made control inputs after a/p loss, and prior to "Lost speeds". If he was flying in ALT LAW at a/p loss, it would seem he was unaware (if his NU was intended). That is unlikely, so he may have made inputs in what was likely Normal Law. All protections, and fly the a/c by hand, in comfort, but without auto pilot. No big.

Did he pull the stick before the stall warning or after? It appears to be "before" in the rude imprecise chronology of the released data.


I agree, and nothing is noted after the "input", said to be left, NU. At the Stall warning, one would think he would relent on the NU (if he indeed knew he was inputting NU) but continue levelling the wings, already underway.

And simply for my own information I have some related questions.

* If he should have waited to apply UAS procedures then how long should he have waited?


Once again, it is not known (though it is strongly suggested) that the a/c had dropped into ALAW, and his wing levelling (and Pitch correction, if intended) was appropriate. At this juncture, it is not known whether the PF continued with his initial corrections, as BEA Say:"...PF made one input...."

* What is the intended purpose of the UAS procedure. It seems to be to slow down the plane to get it into a safer margins condition between stall and overspeed, which was already happening.


One thing, afaik, Stability. Each of the logged incidents has a somewhat different and "ad lib" recovery. Here, the argument against BUSS loses credibility, "It eliminates Anemometric input until landing." Well, speeds are gone, and if they come back, fine no need for BUSS? But if they do not, the need is for speed data for a long safe home, and BUSS might be just the thing.

* Might the pilot have asserted the "slow me down quickly" planning to lose maybe 50 knots by climbing 500' to 1000' and then level off only to have the stall warning derail his thought processes?


I doubt it. The consensus at brief was climbing was ill advised, due warm temps. But that was for a discretionary climb, and as you say, the need for urgent loss of velocity is not eliminated.

* Is everyone happy with the UAS scenario PJ2 suggests?

I am. It was PJ2 who let me know that a vanilla loss of autopilot does not degrade Law, the ship stays in Normal. Now "A/S reads unreliable" was noted eleven seconds after a/p drop. If uas was the deal, a/p would have been dropped at AD disagree, and that would have occurred, of course, prior to loss of autopilot. "I have controls" (after loss of a/p) is first, "Alternate Law" 11 seconds after. It may be merely an anomaly of CVR. I have not seen it explained yet, however.

One does not know, without DFDR data, the accelerations on and around the airframe. A/P disconnect is the first item on UAS c/l. Airbus does it automatically. The AutoPilot also drops out when it cannot keep up with its own manuevering limits.
 
Old 10th Jun 2011, 00:34
  #1719 (permalink)  
PJ2
 
Join Date: Mar 2003
Location: BC
Age: 76
Posts: 2,486
Received 2 Likes on 2 Posts
Machinbird;
'm not sure Do Nothing was a valid course of action either.
By "do nothing", I didn't mean literally sit there, hands-off doing nothing , I meant that the airplane had to be hand-flown like a real airplane, maintaining, (not changing) pitch and power, and kept that way in stable flight until things settled down, and the checklists were called for, etc.

JD-EE, take a look at the BEA Reports, (first one I think) for the UAS drill and checklist.

At the MSA [Minimum Safe Altitude around the departure airport], and the aircraft is well away, either in the climb or in cruise and above FL100, one doesn't "wait" for a while to do the drill...one does not do the drill at all. One "levels off", and begins troubleshooting, which means get out the checklists for pitch and power to stabilize the airplane in cruise. There is not sufficient data to determine if this was done or not - we just have the back-stick and the climb.

Turbine D;

I've slowed down to turbulence penetration speed many times. The power change is minimal, the speed change from M0.83 to M0.80 is, (on the road & going from memory) about 9 or 10 kts. Cruise CAS was around 273kts and the stall speed IIRC, was around 196 kts - Bump speed was around 265 kts or so, so both power and speed were a long way (in level cruise flight) from permitting a possible "rapid" degradation of flight conditions, even in heavy turbulence, (which they weren't in). However, a pitch-up of ten degrees at that altitude is unthinkable as the result would be known intuitively.

I hope that helps...
PJ2 is offline  
Old 10th Jun 2011, 02:08
  #1720 (permalink)  
Thread Starter
 
Join Date: Jan 2005
Location: W of 30W
Posts: 1,916
Likes: 0
Received 0 Likes on 0 Posts
FCOM quotes for supplementary thoughts ...

FCOM3 - supplementary techniques - flight controls

ALTERNATE LAW
Roll
Roll control is direct. The roll rate is generally higher than with normal law and, at first, the aircraft appears to be very sensitive.


An aural "stall, stall" warning continuously sounds at low speeds in altn or direct laws.


When the stall warning stops, the pilot can increase back pressure again, ...

Last edited by CONF iture; 10th Jun 2011 at 03:04. Reason: Title mod
CONF iture is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.