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AF447 Thread No. 3

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AF447 Thread No. 3

Old 29th May 2011, 16:57
  #581 (permalink)  
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Pure lack of proper training
Maybe .. but where have training ?
Certainly not in a simulator (simulators not able to mimic correctly the aircraft out of flight domain)
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Old 29th May 2011, 17:04
  #582 (permalink)  
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I see it quite a bit differently. The Data released is sufficient to frame what happened.

1. Aviation is a complex pursuit. Flying is not complex. Please keep in mind that man has engaged in Heavier than air flight for well over one hundred years.

2. Notice all progress has been accomplished by utilizing ever more complex systems to accomplish what is very basic. Air is the same, Weather is the same.
Power, airframe and control are explored and utilized into the corners of what is possible.

3. Physics does not change, and some are seduced into thinking complexity will some how fool Physics.

4. Those who have the presence of mind to know Physics is bulletproof, may be seduced into thinking the Human can be trained beyond his limitations.

5. Those who remain unfooled, retain an open mind, and listen not to the hype.

6. BEA know exactly what happened, and could explain it in layman's terms yesterday.

7. Time Wounds all Heels.

ps. Save one's sympathy not for the poor dears in BEA, but for the victims of man's hubris.

pps. NO ONE deserves applause for doing what they are expected to do.
Old 29th May 2011, 17:20
  #583 (permalink)  
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The Data released is sufficient to frame what happened.

I sincerely hope you are wrong. However, the same thought had occurred to me.

Regarding 1 to 7; I concur.
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Old 29th May 2011, 17:21
  #584 (permalink)  
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Hyper my apologies - I missed the conjunction between attitude and AoA which indicates more or less level flight at that moment.

The English translation I was seeking was to try to understand the "manoeuvre d'urgence" procedure.
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Old 29th May 2011, 17:29
  #585 (permalink)  
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some positive feelings courtesy of Henra

Thanks, Henra. Good points about overall static stability and such for the 'bus.

Note: Would still interest this old FBW dinosaur to see the pitch moment coefficient graphic for the 'bus, especially in the configuration BEA has determined.

For all: I only present the older FBW system and aero to demonstrate that it is possible to enter a stall that goes and goes and goes unless the crew DOES SOMETHING that the plane allows.

Henra is correct about the c.g. difference and the all-moving tail control surfaces. In our case, we simply did not have enough pitch authority and our cosmic control laws did not allow us to move the stabilators directly. Further, above 29 - 30 deg AoA the rudder was "taken away" from us as the engineers didn't want us to enter a spin ( inverted, we still had control of the rudder as the 'bus does in most laws and same for positive AoA below 29 - 30 degree). Hence, initial recognition of the "dreaded" deep stall was a problem until we all got "educated".

Henra is correct about static stability comparisons. Ours was no-kidding negative until above 0.9 M. Later models, with the big tail, had more pitch authority at slower speeds, but the static stability was almost the same. You could still get into a deep stall with the big tail. I doubt the 'bus has any flight condition with negative static stability. Might have less than other types, but still positive.

So what's your point, Gums?

My point is that the 'bus has more reversion sequences than the jet I flew. I guess to be certified to fly it, one must be able to recite all the sequences and "protections" lost versus actually describing the laws as we had to do. And then appropriate crew actions that won't make things worse.

It has more A/P commands for stuff I find more of a crew function.

It has nothing like our MPO switch to get us to a less complicated set of control laws, but still have more "protection" than a basic "direct" mode for all control surfaces. Fact of life with FBW, and this old dino would not want a plane like the Viper to have such a mode because we had a very expanded envelope and could DESTROY THE JET, as well as ourselves, if we yanked too hard or mis-applied the controls.

gotta go fishing now, later.

Gums sends...

Last edited by gums; 29th May 2011 at 19:44.
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Old 29th May 2011, 17:41
  #586 (permalink)  
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Pitot tubes can be clogged by dust, water or ice cristals because air flows inside from their inlets to their drain holes.

I imagine a tube w/o a drain hole, fed from the aircraft by a variable presssure air pump, controlled to deliver a fixed air flow. The internal pressure is a function of the outside total pressure at the tube inlet, therefore the air speed can be measured.
Side benefit: a simple test on the ground can detect clogging by insects or scotch tape.
Only problem with this concept is that what happens to the water droplets that inertially fly through the outflowing air at the pitot inlet and accumulate.

The existing holes appear able to clear the water out of a full tube in 2 to 4 seconds at 270 knots based on an experiment I did last year with an old airline style pitot tube.

The better solution is to actually monitor the outflow of the tube drains, as suggested by JD-EE. The technology to do this exists. Loss of outflow means the tube is producing invalid data.

With that information, you could crank up the heat in the tube to a very high level and send information to the system to disregard that data for the event duration. And if the fault persisted (bug in the hole) send an ACARS message to get it fixed. That way you don't keep flying with blocked drain holes.
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Old 29th May 2011, 18:02
  #587 (permalink)  
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"BEA know exactly what happened, and could explain it in layman's terms yesterday."

How right you are. If their reason for only releasing the limited info was to placate the media and stop leaks, I fear that the opposite will happen. I can't imaging Le Figaro et al sitting back and waiting for July.
I can see Euros being waved under the noses of those 'in the know'.
I wonder if mm43 can relocate to France to get some insider info, which he seems to be good at?
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Old 29th May 2011, 18:08
  #588 (permalink)  
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Suppose it is what it is . . .

1. Suppose BEA released what it considers to be an honest presentation of the salient portions from the CVR and what has not been released does not contribute to understanding the events.
2. Suppose Pitot failure and inappropriate inputs conspired to deliver a stalled aircraft at high altitude, trimmed full-up, in an unrecoverable configuration. Lack of situational awareness, poor stall warning logic, possible confusion over laws and trim conspired to ride that configuration to the surface.

It is painful, but I for one am going to take it at face value until more information is released. In the meantime, I hope to be proven wrong.

Last edited by MountainWest; 29th May 2011 at 18:14. Reason: added 'and'
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Old 29th May 2011, 18:09
  #589 (permalink)  
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Originally Posted by milsabords View Post
Pitot tubes can be clogged by dust, water or ice cristals because air flows inside from their inlets to their drain holes.

I imagine a tube w/o a drain hole, fed from the aircraft by a variable presssure air pump, controlled to deliver a fixed air flow. The internal pressure is a function of the outside total pressure at the tube inlet, therefore the air speed can be measured.
Side benefit: a simple test on the ground can detect clogging by insects or scotch tape.
There is such a device for measuring level in a tank - cheap and electrically 'intrinsically safe' known/marketted for nearly a 100 years as a Pneumercator. Basically you set a small bleed flow via needle valve/ float gauge and you can calibrate a remote pressure gauge to display tank level.
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Old 29th May 2011, 18:10
  #590 (permalink)  
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Why have an inlet at all? A diaphragm of flexible material covering a void at some set Pressure. The deflection of the 'Tympanum' is the a/s. In another application, perhaps a "particle separator"? Very important (expensive) Helicopter kit. At these temps, it really isn't ice, it is more like "sand"?
Old 29th May 2011, 18:12
  #591 (permalink)  
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Manoeuvre d'urgence / emergency maneuver

No problem BOAC, at that time, the rotating speed vector was indeed crossing the horizontal (making the AoA and the pitch angle equal... to 16°), the beginning of the catastrophic descent.
Unfortunately, as said before, the english version of the 1st BEA report does not translate the C/L "unreliable IAS / ADR check proc" and the emergency maneuver (manoeuvre d'urgence page 121 of the 1st BEA report).
The emergency maneuver (memory item below) may be implemented in cruise phase (above FL100), in an unreliable IAS context, if the safety of the flight is deemed jeopardized:


Below THR RED ALT: TOGA/12.5°
Above THR RED ALT: CL/10° Below FL 100
.....................................CL/5° Above FL 100

PS) 5 days after the AF 447 crash, AF's safety direction released a note to all the navigating crews urging them not to apply this emergency maneuver in cruise phase: http://www.eurocockpit.com/docs/INFO_DIV_AIRBUS.pdf
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Old 29th May 2011, 18:18
  #592 (permalink)  
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Perhaps a few readers may be interested in the following table of data that can be derived from BEA's Update. The times are generally those given at the beginning of the paragraph of the Update, except that 2:11:06 is 15 seconds later. The last line shows (for 'experts' only) the total energy, expressed as a flight level. The speeds at FL0 assume no wind.

P.S.: ChristiaanJ - well said. Imho BEA has released more information than could reasonably be expected at this very early stage of data analysis.

BEA Update 27/05/2011

Time 2:10:05 2:10:16 2:11:06 2:11:40 2:14:28
FL ... 350 ... 375 ... 380 ... 350 .... 0
Mach . 0,81 . 0,68 .. 0,60 ... 0,40 .. 0,23 ???
kCAS . 275 ... 215 ... 185 ... 130 ... 151 ???
kTAS . 479,5 . 399,6 . 350,6 . 233,5 . 151 ???
V/S - fpm 0 .. 700 .... 0 ... -10000 . -10912
alpha . 2,7 ... 4 .... 16 ..... 40 .... 61,2
gamma . 0 ..... 1 ..... 0 .... -25 .... -45
theta . 2,7 ... 5 .... 16 ..... 15 .... 16,2
TE-FL . 452 .. 446 ... 435 .... 374 .... 10

Last edited by Jetdriver; 29th May 2011 at 19:05.
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Old 29th May 2011, 18:38
  #593 (permalink)  
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Over 30 pages on this thread so far have dealt mainly with technical issues and yet there appears to be very little written on what might turn out to be the real cause of this tragedy..... "Airmanship".

Long story short, AF447 was clearly put in harms way. To place an airliner in a tropical line of 55,000 ft+ cells is beyond comprehension. I would be interested in hearing the opinions of other heavy transport operators with experience in ITCZ crossings.

1) Did the tight fuel situation for this particular route play any part in avoiding what appears to have been a required 150+ mile detour that night?

2) What line oriented experience regarding the effective use of wx radar did these pilots receive? Simulators and manufacturer's manuals can't tell you everything...hands on experience is required.

3) How much hands on / off autopilot time did these pilots have and what high altitude stall recovery training had they received?

The Satellite wx overlay place this flight in the middle of a 55,000 ft CB encountering severe turbulence at the time of loss of airspeed information....a daunting situation for even the most seasoned airman.
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Old 29th May 2011, 18:39
  #594 (permalink)  
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TOGA & 5 degrees pitch

It has been suggested on one or more of these threads that the corrective action in the event of airspeed failure above FL 100 is: TOGA and 5 degrees pitch.

(see also: Air France Crash Investigator Examines Airbus Emergency Drill - Businessweek

"... The Airbus maneuver instructs pilots to climb at a five- degree pitch attitude -- the aircraft’s angle above horizontal -- when airspeed readings become unreliable anywhere above 10,000 feet (3,048 meters). Only later in the procedure are they told to check whether it’s safe to level off ..."

Can anyone confirm this ?

If accurate, I suggest that the following might have been the initial reaction in the accident sequence:

1. following AP/AT disconnect, the PF took control (makes sense)

2. eleven seconds later, the PNF says: "so, we’ve lost the speeds" then "alternate law ..." (again makes sense)

3. if the procedure detailed above is correct (and I emphasize that I do not know if it is accurate) then would it not make sense for the PF to assume he was experiencing an airspeed failure and thus, following procedures - TOGA and 5 degrees pitch ?

This might explain why the PF decided to climb, also perhaps thinking that he still had stall protection.

Hopefully, the full data/CVR release will shed more light.
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Old 29th May 2011, 18:57
  #595 (permalink)  
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Why have an inlet at all? A diaphragm of flexible material covering a void at some set Pressure. The deflection of the 'Tympanum' is the a/s. In another application, perhaps a "particle separator"? Very important (expensive) Helicopter kit. At these temps, it really isn't ice, it is more like "sand"?
Bearfoil, not a bad question at all.
The tympanum (diaphragm) concept has some limitations but could work under limited conditions.

Limiting factors would be surface icing and any significant angle of attack-Alpha or Beta.

The void behind the membrane would likely be liquid filled to transmit pressure directly to the transducer. The liquid would have to remain liquid under all flight conditions, and the thermal expansion characteristics would have to be moderate.

The shape of the membrane would have to be such that you had stagnation pressure over the entire surface area.

The system would not work well at significant angles relative to the airflow since the stagnation point would not stay put.

Finally rupture of the membrane or other system leakage would unsupport the membrane and would cause system error. Use of a gas behind the membrane would not work because of PV=RT.

A better approach would likely be a small diaphragm with built in strain gages mounted on some sort of projection that gets it out of the aircraft's boundary layer. In essence moving the transducer out to the surface of the aircraft.

Dust separator concepts would take away from the stagnation pressure. You would probably want something in front of the transducer diaphragm that resembled current pitot tube openings to ensure capture of actual stagnation pressure-but that leads us circularly back to the present design, heating, drain holes and all, with the transducer closer to the scene of action.
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Old 29th May 2011, 19:09
  #596 (permalink)  
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Any Similarities ???

I went back to look at an old Post #825 by oldengmkr, Page 42, AF447, Thread #2. This was the A-330 / A-340 incident over the North Atlantic in October 2000. Now I do recognize that there are differences to start with, the A-340 speeds were accurate, whereas, the AF447 speeds were erroneous at the onset of the incident. However, if high speed sensing initiated the AP & AT coming off in both the A-340 and AF447, could, the events, at least initially, be similar to a degree? Just asking...

Excerpts from the A-340 incident:

Shortly before the AIRPROX event he experienced moderate turbulence and noticed outside air temperature changes. Suddenly the aircraft began to climb, the Master Warning sounded and the autopilot self-disengaged as the aircraft exceeded the speed limit of 0.86 Mach. The indicated airspeed dropped below VLS (the lowest selectable) as the aircraft climbed and the commander took manual control of the aircraft because neither autopilot would engage.

Five seconds after the autopilot disengaged, the thrust levers were closed and then the autothrust was disconnected, probably by the handling pilot in an effort to prevent another overspeed condition. Ten seconds after the autopilot disengaged, the corrected or phase-advanced angle of attack (a computed parameter which is not recorded but can be calculated by Airbus Industrie from the DFDR data) reached the 'alpha prot' value. This angle of attack excursion beyond alpha protcaused a change in the pitch flight control law from normal law (NZ law) to angle of attack protection law (AoA law). If both sidesticks are at neutral, the AoA protection law seeks to hold the angle of attack constant at alpha protuntil a sidestick pitch command is made. If the stick is pulled fully aft then the angle of attack increases to alpha max. If the sidestick is not moved aft, AoA protection law remains active until a nose-down command greater than half forward travel is made or until a nose down sidestick input has been applied for more than one second. The first recorded sidestick input was made at 14:22:08 which was some 28 seconds after the commencement of the Master Warning. For 18 seconds after the autopilot disengaged the aircraft remained within 200 feet altitude of FL 360 but once AoA law was invoked at 14:21:50 hrs, the aircraft's attitude began to pitch nose-up. The pitch-up trend continued for 17 seconds reaching a peak of 15° nose-up shortly before the first nose-down sidestick command was applied. Throughout this phase the aircraft climbed rapidly (reaching a peak rate of about 6,000 ft/min) due to the increase in lift created by the flight control system's capture of alpha prot. The aircraft reached its apogee at FL 384 at 14:22:28 hrs where the airspeed had decayed to 205 KIAS and 0.67 Mach even though full thrust had been applied. Throughout the turbulence encounter, the normal g fluctuations were between 0.5g and 1.5g. The recorded wind direction remained within 20° of the mean of 240° but the wind speed varied between 67 kt and 108 kt and the static air temperature fluctuated between -42° C and -52°C. There were 7 cycles of temperature change, the second cycle being the most severe. The mean air temperature before the AIRPROX event was -46.5° C and afterwards it was -44.5°C. The crew subsequently descended back to FL 360 and successfully re-engaged the autopilot and autothrust systems.
The DFDR recorded a change from TCAS TA to RA at 14:21:41 which was about one second after the Master Warning started. The RA persisted in the aircraft logic for 27 seconds by which time the aircraft was climbing rapidly through FL 372. The alert then changed to a TA which persisted for 8 seconds, ceasing as the aircraft climbed through FL 378.

Angle of Attack protection law
Once AoA law is active, rearward movement of the sidestick controls angle of attack between alpha prot (neutral sidestick) and alpha max (full aft sidestick). Forward movement of the sidestick disengages AoA protection law and the system reverts to normal pitch law. However, there is no aural or text message which informs a crew that AoA protection law has been invoked. If the sidestick is not moved from its neutral position, the pitch flight control system is programmed to capture alpha prot and not the airspeed that corresponds to alpha prot in 1g flight. Consequently, in turbulence the speed scale will probably be oscillating, the aircraft pitch angle could also be oscillating, and the change from normal pitch law to AoA protection law could be difficult to detect.
The commander's reported sighting of an 'Alpha Lock' message was probably an alpha floorwarning on the flight mode annunciator portion of the PFDs. Alpha floor is an autothrottle function which applies full thrust, irrespective of the position of the thrust levers, if the airspeed is likely to reduce to a value approaching alpha max. In this incident, the A340's calibrated airspeed decreased from around 270 kt before the turbulence encounter to 205 kt at the apogee of the climb.

Aircraft response to turbulence
Changes to the A340's flightpath caused by the aircraft's flight control system response to the overspeed warning and autopilot disconnect were negligible until AoA law was triggered. The fact that this law was not triggered until 10 seconds after the autopilot disconnected was a random event driven by the severity of the turbulence. Had the turbulence been more severe at the first encounter and coincident with the overspeed warning, reversion to AoA law could have been triggered as soon as the overspeed condition disconnected the autopilot. Nevertheless, it should be noted that had the autopilot remained engaged, the AoA law would not have been invoked because it is inactive except in manual control. Such was the vigour of the A340's climb in AoA law, the aircraft could well have climbed through FL 363 (thus provoking a TCAS RA with revised software version 7.0) in a very short time, even if the crew had applied nose-down sidestick as soon as they heard the (delayed) autopilot disconnect warning.
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Old 29th May 2011, 19:11
  #597 (permalink)  
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Not a pilot problem...

Why this case is a design concept problem and not a pilot problem?


If only 1% of qualified pilots get a wrong picture of what is going on in this scenario then it's not a pilot or training problems but a design problem in the way of data presentation to the pilots.
Additional point: If all systems are okay but only one input data (air speed) is invalid then there is no reason to disable the autopilot because the pilot don't have a better speed value.

Following this thread since two years as silent reader I have the advantage not to be a pilot but many years of IT design experience. This helps to identify problems from another point of view.
I am a graduated physicist and have been working as software developer for 25 years with industry quality data IT-systems including data input screens, automatic machine date interfaces and graphical presentation.
During all the thousands of IT-duty calls I got at day and night helped me to develop a good feeling what can go wrong between hardware, software and the user - and how to avoid this.

Main problem in the system design phase:
The programmer speaks with the wrong persons (not the end user) or got a system specification written by people not knowing all cases. Especially big companies avoid direct contact between the programmer and the end user.
The resulting produced software is working well for standard cases but in case of problems the error handling will be poor.
Only the end user knows all special cases and possible combination with other systems. The programmer has the task to find out what the user really needs and only he knows which additional help data the system can give to the user.
Note: A good written program often has more than 50% code for error handling.

Example: >>> The user wants to print a sheet with quality data but nothing happens.

Bad written software will show nothing or display some cryptic error codes.

A smart program collects all errors, adds a priority to each error and does some additional plausibility checks to eliminate errors that are results of other errors.
In our sample the problem can be missing data, database server, network switches, network connection, print server, wrong printer, printer defect, paper missing,...
A good program also checks the printer queue for errors, tries network pings to check the connection and so on.
Then the error codes are checked for logical relations and finally an easy to read, short message for the user is generated.
This message should show what action was requested, what went wrong, the assumed reason and how to fix it:
Sample: "Cannot print because network connection to printer lost -> check network cable (main reason for cable problems: cleaning lady). "
This message box also has a "Help" which will show a picture where the PC network port is located. So the user is able to fix the problem without calling me at night...
Another important rule: A good system should never surprise the user - it should always let you know what happens next.
So when the problem is fixed the program should inform the user "Connection to printer OK - print again?"

Back to AF447:

The pilot seems to have wrong picture of the situation (never see the changing stall messages as valid) which results in wrong actions.

So the question is: which presentation of the available flight data will create a correct picture for the pilot?

The current cockpit instrument are looking old fashioned to me, similiar to old Comodore64 text adventure games I played 25 years ago:
A lot of numbers displays, cryptic messages give the brain a difficult task to generate the matching picture.

So just some thoughts:
1. Present a graphical 3D-Model of the plain that show the xyz-orientation as well as air-speed, GPS ground speed and attitude arrows (unreliable or
dangerous data marked by colors)
=> so that even a non-pilot can see in seconds what is going on.
2. imagine an IPAD-like touch screen device showing this 3D flight model that you can turn and zoom with your fingers.
3. put all manuals/checklists into this device - in case of a problem the matching checklist is shown automatically. The pilot has confirm the suggested actions (Trim/Thrust settings) just with a tip of his
finger to automatically executed them.
4. show detailed logs what the system is doing in case of unusual data.
Also use text to speech computer voice (see 100$ car navigation devices) to speak the messages.

Sample messages:
- unexpected speed lost => Thrust changed to 90%
- cannot hold speed with 100% thrust
- speed unreliable, possible cause: pitot icing (because of temperature, all 4 tubes)
- change to emergency mode:
using GPS ground speed before unexpected speed lost as reference

Then show check list for unreliable speed and ask for execution.

Hope this helps for the discussion...
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Old 29th May 2011, 19:13
  #598 (permalink)  
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Wake up call

How about putting a stall warning horn in the rest quarters?
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Old 29th May 2011, 19:16
  #599 (permalink)  
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Originally Posted by HazelNuts39 View Post
BEA Update 27/05/2011

Time 2:10:05 2:10:16 2:11:06 2:11:40 2:14:28
FL ... 350 ... 375 ... 380 ... 350 .... 0
Mach . 0,81 . 0,68 .. 0,60 ... 0,40 .. 0,23 ???
kCAS . 275 ... 215 ... 185 ... 130 ... 151 ???
kTAS . 479,5 . 399,6 . 350,6 . 233,5 . 151 ???
V/S - fpm 0 .. 700 .... 0 ... -10000 . -10912
alpha . 2,7 ... 4 .... 16 ..... 40 .... 61,2
gamma . 0 ..... 1 ..... 0 .... -25 .... -45
theta . 2,7 ... 5 .... 16 ..... 15 .... 16,2
TE-FL . 452 .. 446 ... 435 .... 374 .... 10
Thanks HazelNuts !

Interesting Data Point!

Back in the old thread I did a calculation based on projected surface of an A330 and a weight of 210t:
You would have to enter the L/D diagram of the A330 at an Alpha of ~45° with 85 kts and see if the combined Lift and drag higher than the 2100 kN (+ thrust of the engines).
That would mean ~1500kN along the trajectory, if no thrust of the engines available (idle, stalled) and ~ 1800kN at Cruise Thrust along the 45° path.
The projected surface at 45° being roughly 520 sqm, at 44m/s you get a resisting force of 620 kN at Cd = 1.
This means the Fuselage + wing would have to have a drag coefficient of ~ 2,5 - 3.
That's definitely too much.
I would expect something around 1.

At Cd = 1 it would mean ~80m/s => ~160kts along the trajectory. =>
~110kts horizontally + 110 kts vertically
I have now new empirical data which is difficult to get from the books
Basically this indicates that the drag coefficient of an airliner in a deep stall (AoA ~ 45°) appears to be close to 1.
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Old 29th May 2011, 19:24
  #600 (permalink)  
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"...Angle of Attack protection law
Once AoA law is active, rearward movement of the sidestick controls angle of attack between alpha prot (neutral sidestick) and alpha max (full aft sidestick)."
So in an emergency escape from CFIT, the bus can go 60 bank and limit there.
Likewise it can go Alpha max, and stay there, safely.

Our 447PF rolled in left bank, full aft stick, and held it. Sounds familiar.


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