As long as we are talking about subsonic flight, for a particular wing configuration, the stall is always at the same AOA, even during accelerated flight (pulling g) which is what makes AOA so valuable. Drop flaps or slats, contaminate the wing with ice, and you have a different configuration. If you are flopping around in a post stall gyration, AOA tells you which way you have to go to get the wing flying again. If there is ever a doubt about the validity of airspeed, AOA will let you know when you are getting near the wing's limits. There is a learning curve to use it, but it isn't very steep.
It boggles my mind to think that you have the probes mounted on the aircraft, and glass cockpits, and yet no one wants to do the little bit of software work to put it on the PFD.
Machinbird

The "Bird" and AoA
 

I agree with Machinbird. It used to be possible to see AoA by consulting AIDS via the MCDU2 on the A320, but - whether or not it still is - that's hardly practicable during a jet upset.

As CONF iture knows well, a good ball-park indication, without any actual numbers, is on the PFD in FPA mode (preferably with the FD switched off). The Pitch attitude angle minus (algebraically) the flight-path angle approximates the AoA. For non-Airbus pilots, the latter is indicated by the "bird" symbol. The snag, for this purpose, is that it also shows any drift in azimuth. So, when there is a lot of drift, it is not directly under the little black box* which represents the nose of the aeroplane.


* [black, but yellow inside]

RE: CONF iture #514
Thanks CONF iture, my estimates where 186 t; ISA+10C
regards,
HN39

AoA on the PFD
 

Just a personal thought on this issue. The average airline pilot will never be in a situation where he has any use for AOA. In recent posts one pilot puts the stall at 12 deg, another at 18 or even more. If a pilot finds himself suddenly in a complex situation where AoA could be really useful, how quickly would his mental processes adapt to using an indication that he has never used before?
regards,
HN39

Off topic for aviators...but I'm sure someone will know
 

Can I just pose a new challenging question (while we wait).:-

As the 2nd or is it 3rd stage of the search is about to begin. Many posters here have postulated the theory that the aircraft may have broken into fairly sizeable chunks before sinking to the bottom.

The perfect solution of course for flight recorder recovery, would have been for it to be torn apart, that way, somewhere on the seabed would be the recorders laying to be discovered, as seems to have been the case in recent accidents.

However, we may well have a near intact rear section of fuselage, probably somewhat compacted due to the pressure depth in which these vital recorders are bolted.

Is it at all likely that an ROV could cut and recover the recorders in this situation or would the whole piece of wreckage have to be recovered to the surface.

This rear section may well have a mass of 10 tonnes and a surface area of 30 sq.m. +
Could it be lifted, how and, what is the physics involved.

:8Bit of surfing has revealed they lifted a 17 ton piece of the Titanic, however they dropped it 2.5 miles back to the bottom the first time due to a storm upsetting the cables.

Well, I tried, bear, where others didn't. There is a great deal in knowing and flying the airplane which cannot be conveyed easily within this kind of discourse. If you didn't pick up the sense for example that the Captain/crew would know that the airplane was in serious diffculty long before indications of an actual stall then perhaps it is my writing that has failed you and, as you claim, "the readership"; if I have contributed to a lesser understanding of the A330 when precisely the opposite was my goal, I sincerely regret that.

You are correct in the exercise of patience because that and a certain forbearance on the part of the readership because print is difficult to convey some notions in, is what it takes to understand the airplane. One cannot convey a sense of the airplane in a few paragraphs so it becomes all to easy to dismiss the airplane out of hand without ever setting foot in it.

To those who fly it, including, clearly, the thirteen crews who successfully dealt with a momentary loss of airspeed data, the airplane is not nearly as antagonistic or obscure as defined in your response.

Anyway, I guess with explanations garnering a "duh" I'm done here and someone else who is willing to spend the time and who has a better comprehension of both engineering aerodynamics and flies the airplane can sit in. Good day.

Bearfoil
 

a tad graceless don't you think ?

Utterly graceless, and I see my failure of communication clearly. The word has taken on a meaning that is perhaps not as disrespectful as some would think it. This may sound like an excuse, and disrespect should deserve the outrage it provokes. I accept it, and offer everyone an apology, a sincere one.

bear

BEA 2nd report lists almost 40 uA/S (due to pitot) incidents on 330/340. All (apart from 447) involved loss of automatics and reversion to alternate law... and not crashing.

Across this thread there have been pilots stating that uA/S / pitot failure is a "non-event", even on this type. Equally importantly, there are a few pilots who have found it not to be - they aren't here to post. This isn't a type (or manufacturer) specifc issue - a number of the latter group were flying boeings.

Acutally I am not (satisfied). It looks like a weak point in current aircraft design and deserves further investigation to see if we can improve on something we've taken for granted for so long. Sticking multiple "redundant" probes (of the same type) out into the same environment provides no redundancy to environmental issues such as icing. The B2 allegedly has 20+ sensors...

All that said, a common factor in the pitot incidents that have gone bad is night-over-water - so maybe the right thing to be focussing on is jet upset and spatial disorientation in general, rather than just one instrument that can lead to it.

Again, this isn't type specific. In other recent incidents the automatics (and this includes the auto-trim discussion) have flown planes to the stall and the parts spread across the landscape have been B, not A.

There is a good general discussion to be had (fragmented across a few threads at present - and maybe deserves its own) on this issue. I do have a feeling that as the industry has given airlines and pilots better and better automatics the, unintended, consequence is that pilots are being barred, by airlines, from flying the plane (SOPs and "safety"). I don't think it can possibly enhance safety if the only time the pilot is handed the controls is when the aircraft is heading out of control - on any type.

A look through the other uA/S incidents shows AP/AThr disconnect and reversion to alternate law. This isn't (or shouldn't be) a "surprise" degradation, or a difficult one to handle, as is evidenced by all the previous incidents (in fact the only thing that "degrades" are the flight control protections which some airbus critics seem to think shouldn't be there anyway).

Reversion to direct law is clearly not a direct consequence of uA/S (see the other incidents). Something else happened (uA/S may have started the incident). Someone (I think it was the pilot union head quoted in Spiegel article) has stated that the pilots initiated the PRIM reset - although how they know this isn't made clear. Obviously it didn't save their bacon whether it was pilot or system initiated - but my hunch is that they were already irrecoverable at that point.

Bearfoil;

Thanks.

With regard to what happened to AF447, whether the pitot/ADR/PRIM issues were coincidental with an unrelated series of handling issues possibly (or not) related to weather, or were the cause of the LOC, there remains much to discuss.

PJ2

CAS and AoA
 

RE: CONF iture #521
IMHO that is not exactly true, but maybe good enough for practical purposes below Mmo
regards,
HN39

Example
An A330, 205t, cg as QF72, 235 kt CAS:

@ FL 350; M 0.7; AoA = 5.2 deg
FL 200; M 0.52; AoA = 6.1 deg
sealevel, M 0,36; AoA = 6.5 deg

This assumes that the lift coefficient/AoA relation derived from the QF72 maneuver corrected for Mach-effect per Prandtl-Glauert does not change with Reynolds.

BEA - Press Release
 

Flight AF 447 on 1st june 2009
A330-203, registered F-GZCP

Press release, 19 March 2010

The « Anne Candies » is now expected in the port at Recife on 24 March.

As announced on 15 March, the BEA will hold a press conference before the departure of the ships to the search zone. This will take place in the presence of the teams of investigators and those involved in the sea and undersea search operation on Thursday 25 March from 14 h to 16 h in Recife in the port administrative buildings in the port area (main port entrance).

Journalists who wish to attend are requested to confirm their presence with Martine Del Bono at the latest by 23 March.

Following this press conference, a media pool will be able to go on board Phoenix International’s « Anne Candies » and the « Seabed Worker » to film the equipment of the US Navy and Geomar, Seabed and Woods Hole Oceanographic Institution (WHOI).
------------------------

mm43

Anne Candies
 

The ship was about 300 miles off Belem this afternoon, at just over nine knots. With about a thousand miles to go to Recife she should be there by Tuesday evening. Allow a few days for victualling, bunkering, spares to arrive etc and she may be off to the search by the end of next week.

AoA/Alt & D.P.Davies
 

PJ2/CONF iture

within reason, (3 decimal places @ representative crz AoA, α ...) D.P.Davies was more or less correct in his statement.

Angle of attack is linearly correlated to section lift coefficient, Cl below separation angles of attack. The correlation of section lift coefficient, a, is dependent on Re, and also ~Mcrit.

Reynolds is dependent on density & viscosity...
Re=(ρ.V.L)/μ;
= (density x mean fluid velocity x characteristic linear dimension)/dynamic viscosity of the fluid.
Total lift is also dependent on density;
L=Cl.0.5ρ.V^2.S

Density is a numerator in both cases, so is not self cancelling with variations...

At low AoA, there is almost no difference in the Cl for Re from 1,000,000 to 8,000,000, but at high AoA, the higher Re results in higher Cl for a given AoA.

At high subsonic MNo, the compressibility effects alter drag (drag divergence) but also alter Cl, for a given AoA, but the outcome is dependent on geometry of the foil.

remaining at normal cruise AoA and below drag divergence, D.P.Davies statement is reasonable that altitude doesn't effect AoA for a given CAS (restated). Humidity does have an effect but is minimal for normal operational conditions.

.................

Ideal Gas Law:

ρ = p / (R * T)

where: ρ = density kg/m3
p = absolute pressure Pa, N/m2
R = individual gas constant J/kg K
T = absolute temperature K

D=((P/(Rd*T))*(1-0.378*Pv/P)

where: D = density, kg/m3
Pd = pressure of dry air (partial pressure), Pascals
Pv= pressure of water vapor (partial pressure), Pascals
P = Pd + Pv = total air pressure, Pascals ( multiply mb by 100 to get Pascals)
Rd = gas constant for dry air, J/(kg*degK) = 287.05 = R/Md
Rv = gas constant for water vapor, J/(kg*degK) = 461.495 = R/Mv
R = universal gas constant 8314.32 (in 1976 Standard Atmosphere)
Md = molecular weight of dry air 28.964 gm/mol
Mv = molecular weight of water vapor 18.016 gm/mol
T = temperature, deg K deg C + 273.15

Links:

http://www.efm.leeds.ac.uk/CIVE/CIVE3400/stvenant.pdf

Equations - Air Density and Density Altitude

luizmonteiro - Altimetry Calculations / E6B Emulator

JavaFoil

Dynamic, Absolute and Kinematic Viscosity



References:

Batchelor, G. (2000). Introduction to Fluid Mechanics

Clancy, L.J. (1975), Aerodynamics, Pitman Publishing Limited, London. ISBN 0 273 01120 0

Kundu, P.K., Cohen, I.M., & Hu, H.H. (2004), Fluid Mechanics, 3rd edition, Academic Press

Ockendon, H. & Ockendon J. R. (1995) Viscous Flow, Cambridge University Press. ISBN 0521458811

Reynolds, Osborne (1883). "An experimental investigation of the circumstances which determine whether the motion of water shall be direct or sinuous, and of the law of resistance in parallel channels". Philosophical Transactions of the Royal Society 174: 935–982

RE: fdr post 535

All very true and interesting, except 'three decimal places ...' - see my reedit of post 532
regards,
HN39

Which was the original point that I tried, although not well, to make. Hazelnuts39, I understand the point you're making; - while not entirely precise and knowing that supercritical wings do not stall uniformly and that atmospheric conditions will cause variations which must be taken into any precise account, nevertheless there is, for practical work using the kinds of displays available on the A330, B777 etc, essentially one CAS for a specific angle of attack. As Chris Scott pointed out earlier in the thread, the angle of attack is represented on the A330 PFD when using the FPV - Flight Path Vector. Hopefully the schematic below will assist in making this a bit more clear. I believe I have used the terminology for actual flight path, (gamma), pitch, (theta) and AoA, (alpha) appropriately - any corrections gratefully accepted. PJ2


http://i277.photobucket.com/albums/k..._2010-03-3.jpg

From the July Interim BEA report:
"FLAG ON CAPT PFD FD and FLAG ON F/O PFD FD (2 h 10)
Symptoms: Disappearance of the Flight Director on the PFDs, Captain and
First Officer sides, and display of the red FD flag.
Meaning: This message indicates the Flight Director function is selected and
unavailable."
Followed by:
"FLAG ON CAPT PFD FPV and FLAG ON F/O PFD FPV (2 h 11)
Symptoms: Disappearance of the FPV (bird) on the PFDs, Captain and First
Officer sides, and display of the red FPV flag.
Meaning: This message indicates that the FPV function is selected and
unavailable."
We don't really know how ACARS prioritized the transmittal of messages, but they could even have been virtually coincident.
Even if you could use this method during routine flight to determine AOA, it wasn't available to AF447 when the going got interesting.
Machinbird

Machinbird;
Yes, I think that would be correct. Other than possibly establishing a stronger situational awareness I would not expect an A330 pilot to use the 'bird' for primary purposes. The schematic is merely intended to describe the FPV presentation and how it works in response to questions on same, earlier in the thread and by PM. PJ2

PJ2
It was only my intention to point out that when you really might need such information as AOA, your customary sources of inferring it would not be available. Once the ADIRU outputs are disqualified, the velocity vector information they provide is removed and the aircraft systems have to make do with what is left (which isn't much).

Much earlier on the other main AF447 thread, there was a posting about an available Airbus system (BUSS-BackUp Speed Scale),(an available option in purchasing the aircraft) that inferred airspeed using AOA and a computer performance model of the aircraft (Post 4041). I'm not sure that even that approach is adequate. Suppose a hail encounter "modified the aircraft" a bit, e.g. removed the radome. Would your AOA sensors then be valid?

If AOA is ever presented in an airliner, I hope there is not too much computer mediation of the display. You don't want a damaged or defective probe or vane causing an accident ( e.g. A310 in Africa), so redundant sources are desirable, but computed AOA involving airspeed derived validation scares me. I've flown a lot with single source AOA indicators and have found them to be reliable and simple to interpret. You do have to pre-flight the probes/vanes but it is just a visual check. The info could be available on your PFD with minimal work, and a few flights/simulator sessions would give you the big picture of how it does its job.

Has anyone ever worked out how many damaged/destroyed airliners might have potentially been saved by providing the crew better AOA awareness? Is that stall warning after takeoff real or bogus? Might be an interesting study.
P.S. Didn't the L1011 have AOA indicators? How did that work out?
Machinbird

Machinbird;
Thank you for your reply. Understand your intention, but while other remarkable developments have occurred the use of AoA in airliners as a primary indication doesn't appear to be widespread perhaps because it just hasn't been a problem. Regarding a survey of accidents, off the top of my head I can recall six accidents in which a stall was involved in the accident sequence; Colgan Q400, Turkish B737, One-Two-Go MD82, Spanair MD82, Empire (FedEx)ATR42, USAirways B737 (Pittsburgh) and possibly AF447. This doesn't include several fatal Bombardier RJ stall accidents caused by contaminated wing surfaces. Of course, no AoA indication is going to assist the crew in the contaminated wing case.

I would like to know what I'm missing about AoA. In my opinion, and I hope HN39 and others will comment, on the surface and except for possibly one accident I don't see the direct availability of AoA to the crew making a difference in these accidents listed above even assuming, obviously, that crews would have been trained to use the indication.

The question and argument here I think is, what does AoA offer that CAS does not. There is the obvious case where 'g'-loading is involved but in considering the accidents described herein the low altitude (around 400') of the Turkish B737 when the secondary stall occurred (I believe due to pitch up from increasing engine thrust) would have made any successful recovery doubtful. It might have made a difference in the USAirways B737 accident near Pittsburgh, providing sufficient information for the crew to "relax" on the elevator just enough to unstall the airplane. That may have been mentioned in the report, I don't know.

BTW the A330 has 3 AoA vanes - Capt., F/O, Stby, with inputs to the three ADIRUs. Not sure you were referring to the A330 present design or to the previous suggestion regarding "computed AOA involving airspeed derived validation scares me". I agree with you even for a backup system, but just to make clear that the A330 system is sensor-derived although the display of the 'bird' is of course DMC (Display Monitor Computer) driven.

PJ2

PJ2
Thank you for your reply. I modified my previous posting a bit with additional information regarding the BackUp Speed Scale option, and a bit more info on an A-310 accident on takeoff which occurred in Africa following bogus stall warning activation.

The reference to airspeed derived AOA validation was only a comment on a possible engineering approach which should not be done. AOA and airspeed are each primary data, and they may conflict for various reasons. This is just the engineer in me coming out and I apologize if it causes confusion.:O
The AOA indication can also be an effective forewarning of a potential bogus stall warning after liftoff. If it is pegged at high AOA while going down the runway, something is wrong with the sensor, and you will know that before rotation, probably even before V1. Airspeed and AOA go together to tell you important data about your aircraft's performance and enable you to cross check each indication. When something doesn't agree between them it can be a serious problem and you need to have an idea which to believe in. If all you have on your panel is airspeed, you are open for an AOA sucker punch (IMHO), particularly on a high wing loading aircraft.
Machinbird

AoA from FPV
 

A related question could be what AoA offers when CAS is not available. If you’ll forgive my idle curiosity in the face of the serious matters you’re discussing, why doesn’t the IRU use inertial vertical speed to calculate FPV, rather than the barometric vertical speed it doesn’t get from an ‘invalid’ ADR?
regards,
HN39

PJ2,
Thanks for posting that excellent graphic of the Airbus PFD in FPA mode. This originated with the Orca (A310) in 1983/4.

I think it may be helpful to some other readers, unfamiliar with Airbus glass cockpits, to clarify what we are looking at.

It is clear in the graphic that Alpha is +15 (but see my penultimate paragraph below). But if the drift increases, and particularly when varying amounts of bank are present, it's not so easy for the eye to interpret quickly.

The second problem is that, unfortunately, we are not looking at a primary indication of AoA, even though that could be made available from the appropriate AoA sensor. The "bird" is dependent entirely on IRU data (from the appropriate ADIRU), as Machinbird pointed out. So, of course, is the pitch indication on the same PFD.

HN39,
As far as I know, the FPA ("bird") derives its data from the IRU, not the AD. I would be astonished if it used VS from the AD, because the latter (presumably coupled with TAS) could only give a trajectory relative to the air – not the ground. When you are using the FPA to fly a steady glide-slope on a non-precision approach (standard procedure in British Airways), the FPA has to be relative to the ground.

Everyone,
My response to HN39 has belatedly reminded me that AoA CANNOT accurately be derived from a comparison of Pitch and FPA (flight-path angle): it is only strictly true in a stationary air mass.


Coming from a purely civil (airline) background, I've nothing useful to contribute on the concept of flying AoA as an alternative (or complimentary) to airspeed. We were just never taught it. To illustrate the point, both the 1960s VC10 and BAC 1-11 (and, presumably, Trident) had AoA sensors for their sophisticated stall-protection systems. But the only time we saw an AoA gauge in the cockpit was when the engineers fitted it temporarily for a flight test, after which it was removed.

Certainly a direct AoA reading would be of benefit. The only experience I have of such is from the Harrier GR3 where you were taught to 'maintain 8 units' during transition to and from slow speed (unspecified 'units' - didn't matter!). Providing one stuck to this rule the actual business of 'transferring' lift backwards and forwards to thrust was simple. Driving the AoA reading from an alpha vane (suitably heated:ugh:) would take away many of the problems caused by the 'sophistication' of modern aircraft systems - let's keep computers and IRS out of it - and if crews were given 'ball park' figures to set to maintain safe flight well away from the stall I can only see a positive safety addition.

AoA from FPV
 

regards,
HN39

Purely as an aside... Concorde did have an AoA gauge, combined with a G gauge (vertical-scale instrument, on the left of the main flight instruments).
I'll have to ask a pilot again, in what circumstances and to what extent it was used and useful.. I honestly no longer remember.

CJ

Thanks, HN39, I'm suitably "astonished"!

Will assume the BEA is right on that point, at least. So the horizontal data (TRK & GS) come from the IRU part of the ADIRU, and the vertical speed is simply the VS supplied by the AD system part. I had overlooked the fact that pressure-derived VS indications moved on a bit during my career, in terms of lag (lack of), as well as accuracy and reliability.

I should not have inferred that you were suggesting the horizontal data was also from the air-data (AD) system – my apologies.

But I agree with you that it seems odd that the displayed FPA/FPV ("bird") does not, apparently, derive its vertical datum inertially, from the IRU.


The rest of my comments still stand to be corrected...

Chris

AoA and FPV
 

Chris Scott:
Thanks for your reply. I agree with the rest of your comments, except that you might wish to rethink slightly:
Barometric VS differs from inertial (tapeline or geometric) VS when temperature differs from ISA. Another reason why the use of barometric seems odd.

PJ2:
I owe you an apology for setting you off on the wrong foot. Although I am used to defining FPA relative to the airflow, the mention of 'drift' should have alerted me to the fact that FPV on the PFD is relative to the ground.

regards,
HN39

Good evening HN39,

The sentence of mine you quote has effectively been rubbished by me, by virtue of my apology above. [I was mistakenly under the impression that you were arguing that FPV was based on TAS, which would have made the FPA relative to the airmass, not the earth.] Am tempted to amend my post, but that seems dishonest, and I doubt it will be read in isolation.

You raise another interesting point about the alleged dependence of the FPA/FPV ("bird") on VS data from the AD. The pressure lapse rate in the atmosphere does indeed vary with temperature deviation from ISA. I suppose the air-data system may correct for that, but that's me guessing again...

The cockpit altimeters do not correct for temperature deviation, presumably to keep all aircraft "singing from the same hymn sheet" for ATC separation purposes, and also because the AD system cannot know the temperature deviation of the entire atmosphere below the aircraft.

HazelNuts39, Chris Scott;
Exactly right, HN39.

So, with reference to Chris Scott's remark, where are we?

We have two cases: One in which the crew sets the FPA and the aircraft follows it under autoflight/FMGC guidance, and one in which the airplane is descending "normally" under autoflight/FMGC guidance either in the "OpDes/FltLvl Chg" modes which are the Airbus and Boeing settings respectively, or a form of VNAV which is typically altitude or airspeed constrained (not following an FPA in other words) and referenced to the destination airport taking into consideration the entire flight planned path entered in the FMGC.

Just so everyone is aware, the use of FPA for descent from cruise is almost never used in routine operations. Some here who don't fly but who understand what's going on here may know why right away but if not its discussed below.

Discussion points numbered for reference only:

1. First, when an FPA is selected by the crew on the autoflight control panel, (I believe for all types and not just the A330), it is defined by and referenced to the inertial platform, (essentially, the aircraft) and is not referenced to the airmass or the aircraft groundspeed. Once we set, say "3.0" in the FCU (Flight Control Unit), the FPA is a physical descent path.

2. Now I understand that airmass characteristics such as temperature and humidity do affect barometrically-referenced data. It is my impression that this data would indeed be corrected for "local" deviations from standard, (understand the comment that the ADIRU's/ADC's cannot know what airmass characteristics are below the aircraft).

3. In other words, while I understand that a fine-grained aerodynamics analysis of the notions set out in para.1 would disagree, neither a pilot nor the autoflight system nor the instrumentation on the PFD/Standbys can expect as an outcome, "3-decimal accuracy" in flight, even though the guidance equipment will likely be sending such fine-grained data to the autoflight system; - it's just not possible with the airmass variations and aircraft inertia involved. But the "approximation" is, (we have to assume, because its all certified and we do it all the time), good for all practical work both enroute and during the approach/landing on, for example, the non-precision FPA approach described above.

4. So back to FPA and AoA, let's assume the crew has selected a 3.0 FPA descent: As the wind component changes and as temperature (and humidity) changes during the descent minor adjustments are made to pitch to maintain the 3.0deg FPA - that means that the IVSI, (Inertial Vertical Speed) changes and of course the AoA may change slightly as well. In other words, the autoflight system will increase/decrease descent and in the latter case even add power to maintain the FPA set by the crew. You can now readily see why we don't use FPA for a routine descent. Both pitch and power are all over the place trying to maintain the theoretical path in space. In busy air, it's a mess and not very smooth for the passengers.

5. In the case where the FPA is set by the crew and the autoflight system flies it, the FPV symbol will be close to the setting because that's what the autoflight system is designed to do. When under VNAV or OpDes/FLCHG guidance, the FPV symbol will still indicate the actual FPA, whatever it is in the VNAV-guided descent.

6. The key here is, even as the descent is taking place the FPV symbol on the PFD indicates actual FPA for the aircraft in real time and so may be (guessing here guys) reliable as a practical working AoA.

7. I'm not sure if this got us anywhere in terms of deciding whether the algebraic difference between displayed pitch and displayed FPA by the FPV symbol is accurate in all cases, (the non-still-air case as described by Chris) but it may provide some grist for further thought. PJ2

Hi PJ2,

Re your item 4:
Wish we understood this "IVSI" better. Is it inertial, or barometric, or a fiendish combination?
Not really relevant, but – in response to your comment – one or two pilots on my (A320) fleet used to use the FPA (AP engaged) for routine descents. They achieved continuous idle thrust by asking the A/THR to try and achieve an IAS of, say, 250, when the selected FPA was good for, say, 300 at idle thrust.

Re items 6 and 7, the following is my best shot.

In still air, including the absence of thermals or downdrafts, the pitch angle minus the FPA represents the AoA (provided, I suggest, due allowance is made for what used to be called the "riggers angle of incidence" of the wing mounting; which is a constant).

In air which is moving vertically, there would be a correction to be made. For example, imagine a jet in the cruise, with pitch +3 and FPA 0. Alpha is +3. Now it enters an area of continuous updraft, and pitch has to be reduced to +2 to maintain FPA 0. But Alpha must have been maintained at +3. If Alpha had reduced to +2, the aeroplane would accelerate downwards due to loss of lift.

The case where the air mass is only moving horizontally ("wind"), also leads to an error. This may be best illustrated by looking at an extreme scenario. Imagine a microlight equipped with similar flight instrumentation to an Airbus (!). It is flying straight and level at a TAS of 50 kts into a 50-knot headwind (GS 0), pitch +3, FPA 0, Alpha +3. Because the aeroplane is stationary in relation to the earth, an FPA of zero would only be possible if the pilot maintains the VS precisely at zero. The tiniest rate of descent would presumably result in FPA -90 (vertical descent), suggesting an Alpha of +93. Similarly, a tiny rate of climb would give FPA +90 (vertical climb), suggesting Alpha -87. But, in fact, Alpha remains at +3.

Not having tried to work out any figures, I don't know how significant these two types of errors would be to a jet pilot, experiencing spurious airspeed indications at high altitude and high TAS, trying to use AoA to recover from an upset. Perhaps not very significant?

In the AF447 case, I presume the predominant upper wind in the area of the accident would have been fairly light; but the thermals and downbursts potentially severe.

FDR,
thanks for your post here but you remind me that I should not have left school that early .... For sure that luizmonteiro link is going straight to my favorites.

What I can say regarding AF447 and the relation between AoA and Indicated Airspeed is that the AoA will vary only marginally for a variation of speed between MMO and VLS.

I mention AoA but I could say Pitch as both match for a A330 in clean configuration for a level flight.

As put by HN39 earlier, maintaining green dot speed which is below usual cruising speeds, will produce a pitch attitude anywhere between 3.5 and 4 degrees. Green dot speed is not that far above VLS, so anything close to 5 degrees already, must be considered very seriously.

In case of erroneous airspeed indication, the crew will not necessarily notice such a minimal variation of pitch on their PFD. And I refrain mentioning turbulence ...

These unreliable airspeed indications at usual cruising flight levels can be a real trap for a crew, especially when the erroneous indicated airspeed is not recognised as such by the system, crew included.
Then you can also take account of the "protections" that may play around, but on the base of erroneous data … :hmm:

I am again finding myself drawn into arcane mathematics and physics here about 'descent' and 'FPA'. Surely the whole point of having an independent AoA indication would be to enable a crew to ensure they are flying a safe AoA (away from any stall angles) in the event of corruption of the electronic wizardry? I do not see the need for such with fully functioning triple IRS and 'correct' IAS inputs.

Certainly trying to work out my AoA from PJ's picture, whilst wrestling with conflicting IAS inputs and possible IRU problems would have significantly challenged me! A simple vane driven display would do that with delightful ease. As with my example with the Harrier, IAS was IRRELEVANT - all that was needed was the magic 8 units from 0 kts to normal wing-borne flight. So easy!

"Seabed Worker" and "Anne Candies"
 

The "Seabed Worker " berthed Recife at 0810m (1110z) 2010-03-22 and the "Annie Candies" ETA Recife is 0800m (1100z) 2010-03-24.

Will advise when "Anne Candies" berths.

mm43

Chris Scott re your post 544

I also have only a civil background and therefore heve never flown AoA in normal operations. However, I used to fly as co-pilot or observer on many VC10 C of A air tests. As I remember, the aircraft was prepared by having a cabin window removed and replaced with a blanking plate on which a vane was fixed. This in turn was connected to an AoA indicator which was mounted in the centre on top of the glare shield. During stall tests to stick push it was always someone's sole responsibility to monitor the AoA indicator and shout if the push had not occured before 15 deg AoA. At which point both pilots pushed like hell!

May I congratulate the various contributors to this thread on some really excellent posts. Thank you!

A numerical example
 

RE: PJ2 #551; Chris Scott #552

Perhaps I can add to Chris Scott’s remarks by giving a numerical example:

Ambient conditions: close to sealevel, ISA, still air (initially)
Airplane: A330, 205t, cg as QF72, airspeed 200 kt CAS (= TAS), AoA = 5.5 degrees

Set thrust to achieve FPA = -3 degrees (down), pitch attitude 2.5 deg up, rate of descent 1061 fpm, maintaining 200 kt.

Next, throw in 20 kt headwind, leaving everything else unchanged, and FPA increases to –3.3 degrees.

To return to FPA –3, increase thrust to achieve rate of descent of 955 fpm, and pitch angle will increase to 2.8 deg up. AoA remains 5.5 throughout because airspeed remains 200 kt.

regards,
HN39

Chris, HazelNuts39;
and,
For me, these two examples make the matter quite clear; thank you both.

BOAC;
Absolutely agree with you. I think it would challenge anyone primarily because, though in now-understood cases where it may work, the FPV symbol was not intended as an AoA indicator. Throw in degrading systems as described and the task would be very difficult indeed.

I have asked myself in the face of many expressed dispositions towards AoA displays (almost exclusively from those who have flown military vice civilian equipment and thus have experience with direct AoA displays) why the industry has not moved in a similar direction given the other significant computing, system and display capabilities now available. In his post #540, Machinbird suggested examining accidents in which the presence of an AoA indication may have prevented the accident through better awareness of AoA. I sought a possible answer, albeit informally, in my response #541 citing six relatively recent fatal accidents which resulted from stalling the aircraft. I thought that an AoA indication may possibly have assisted the crew of only one accident, the USAirways B737 near Pittsburgh. Unless associated with sufficient and unmistakble warning, (we are into complexity and computers again), it appears as though the availability of an AoA indication would not have assisted, for example, the THY B737 crew. The Colgan case is similar in this regard as again, airspeed was permitted to bleed off and it is difficult to know if the either crew would have responded to another, different indication. It is clear to all that an AoA indication would not have prevented accidents in which the stall resulted from a contaminated/damaged wing.

It is interesting that, from the discussion anyway, only military aircraft appear to have AoA displays as standard. Would this point to the fact that military aircraft are operated much closer to aerodynamic extremes than airliners and that the benefits of having such information do not outweigh the cost? I can only speak from my own airline experience and the need for a direct AoA display was never apparent.

I am certainly not arguing against the display - the more information the better providing it is unequivocably clear to the crew and they are trained to use the information effectively; Given the many comments however, I am trying to understand why the display has never been installed in civilian airliners.

Whether such information would have assisted the crew of AF447 is of course speculation. However, given the large speed difference between a M0.80 cruise CAS and VLS (about 60kts and another 20+kts or so to the stall) it is difficult to comprehend a situation, even in most turbulence (unless direct entry into a cell), in which airspeed is lost that, as per QRH memory items, setting power, flying pitch in alternate law, (not difficult) would not in and of itself have stabilized the situation. I can't help but wonder what else went on that so severely destabilized the airplane.

PJ2

All your detailed comments on how the FPV is working are certainly interesting, but as the ACARS messages might suggest, the AF447 crew has probably tried to get the help of that bird to stabilize the situation ... but the bird was just INOP !

The only available tool was a pitch and a thrust setting.

As PJ2 said, the bird is not usually used in routine descent or cruising phases. Its utilization is more dedicated to approach phases, a great help, almost magical to stabilize an non precision approach, a bit like having a flight director on its own.

To think that the bird was selected at FL350 makes me believe that the crew was looking for some kind of certitude. The FPV red flag was probably not what they were expecting ...

CONF iture;
It would be unusual but I didn't get the sense from the ACARS messages that the crew was actually using the 'bird'. I believe the ACARS receives/records failure messages for transmission independently of crew selection of such system. Such messages are based upon system capability and availability and wouldnt' wait until the crew had selected the system before recording/sending such a message.

PJ2,
Please read the extract from page 50 in the interim report :

http://i65.servimg.com/u/f65/11/75/17/84/aoa_0010.gif