Lonewolf_50, TAT probe freezing.
This is (was) a ‘relatively’ common problem occurring on several aircraft types. It was most prevalent on the BAe146 which suffered engine roll back due to ice crystal icing in the compressor – all engines since modified.
The most usual erroneous TAT indications, as with the A330 incident, are where the temperature stabilises at zero (ice or water ice) due to the blockage. The temperature change is relatively slow in comparison to the assumed ‘near instantaneous’ pitot blocking.

“…seeing alt low a few hundred feet … prompts pilot to make what is initially a small correction to climb back to FL350?”
Yes, very much my point; this would provide a reason for the initial nose up input, but not answer the subsequent control actions.
Amongst this we should consider that the FDs had probably failed (cf VH-EBA), thus the crew might be looking for a cued parameter to follow. Also, consider what the VS might show after an ‘instantaneous’ 300 ft descent and attempted recovery (inertial / air data mix IIRC).
What happens to Mach No? cf VH-EBA.
What happens to MMO/VMO computation? It’s most likely to be independent of the airspeed display as the value is also used by the FWC for audio warning; would the warning still work?

As for IRU, I knew of one design which had an air data correction in the unit (I forget why), but during testing, a sharp pull up with a rapid loss of speed and quickly increasing altitude caused the ADC software to detect a ‘failed’ (out of tolerance) condition and shutdown both ADCs, which in turn shut down both IRUs. The system design was changed before certification!
The point is that ADC seems to get into many dark corners of modern systems, thus we might not be sure of what the effects of simultaneous ADC malfunction might be.

safetypee: much obliged.
Were such an anomaly to have the capacity to muck up a pitch and power response ... :eek:

FAA Proposes Airspeed-Sensor Fixes
 

FAA Proposes Airspeed-Sensor Fixes - WSJ.com

Hear ! Hear ! ( see also #1567 )

Yup to Speedbird. Just blurking here. AB (and Boeing) pilots will get something constructive out of the final reports, and as a very old SLF I will be grateful. The rest is dross.
My days ended with dinosaur blood. Cannot relate to all this FBW stuff, but judging from you guys, it mostly works. Think back, you aulde guys, to what a handful a DC-4 could be in rough wx.

Extract below from the BEA's report on the 2008 A320 Air New Zealand accident at Perpignan. Also an excerpt from the CVR transcript covering the last few minutes.

The BEA, on this occasion, seems to have concluded that the THS going to 'full up' made it impossible for the pilots to get out of the stall even with the sidestick fully forward; but that the pilots apparently simply didn't see the need to re-trim. It also says, rather poignantly, that they 'did not understand the behaviour of the aeroplane' - a point that is very clearly illustrated by the CVR transcript.

I wouldn't be at all surprised if the eventual report on AF447 says very similar things.

Full report available for download here.

http://www.bea.aero/docspa/2008/d-la...a081127.en.pdf

Quote:

---

15 h 44 min 46 Okay here we go
15 h 44 min 49 Und ich sag ihr jetzt dass wir im Moment in Dreitausend bleiben
The weight is fifty four
And I say now to her that we are maintaining three thousand at the moment
15 h 44 min 51 Golf X-ray Lima triple eight
Tango can you speed reduce speed again
15 h 44 min 56 We are reducing
15 h 44 min 57 Triple click
15 h 44 min 58 ��We are still reducing the speed Golf X-ray Lima triple eight Tango (*)
15 h 45 min 03 (*) I will say when the trim stops
The word “stops” is stronger than the rest of the phrase
15 h 45 min 05 SV: Stall ( x13)
Cricket (stall warning)
15 h 45 min 06 Stop ! Noise similar to thrust levers being moved forward to the stop
15 h 45 min 13 (oh oh oh)
15 h 45 min 18 (…)
15 h 45 min 19 End of stall warning
15 h 45 min 20 Single chime
15 h 45 min 24 Ich nehm die Speed noch mal hoch ja?
(I increase speed ) Yeah?
15 h 45 min 26 Ja it's pitching up all the time
15 h 45 min 27 (…) Stick forward (*)
15 h 45 min 29 Pitching up
15 h 45 min 30
15 h 45 min 31 It’s (*) alpha floor we’re in manual Single chime
15 h 45 min 33 It's pitching up this (…)
15 h 45 min 34 Kriegst du das geregelt? Are you able to handle this?
15 h 45 min 35 Nee No
15 h 45 min 36 Gear up SV: Stall (12 times)
15 h 45 min 37 Gear up Cricket (stall warning)
15 h 45 min 39 Gear up Gear up
15 h 45 min 40 (*)
15 h 45 min 42 (…)
15 h 45 min 44 (…)
15 h 45 min 45
15 h 45 min 47
15 h 45 min 48
Golf X-ray Lima triple eight
Tango contact tower one one eight decimal three bye
End of stall warning
Single chime
15 h 45 min 54 What’s wrong here
15 h 45 min 55 Flaps up
15 h 45 min 57 (*)
15 h 45 min 58 Flaps up
15 h 46 min 00 End of stall warning
15 h 46 min 00,5(*)
Continuous repetitive chime
15 h 46 min 02 Speedbrakes
15 h 46 min 02,5 End of CRC
15 h 46 min 03 C chord (Altitude alert)
15 h 46 min 04
SV: (*) terrain terrain
15 h 46 min 05 (…) (…)
15 h 46 min 06
15 h 46 min 07 End of recording

---

Also, the Perpignan A320 was, I think, being piloted by very highly experienced Type Rating Examiner; the guys who really know their aircraft inside out.
I agree with the assessment above, something not good about THS's that trim themselves full or nearly full NU and then remain there when it might be appropriate for them to auto-nose down to help overwhelmed pilots in the heat of battle with FBW systems..... not to mention stall warnings that shut down at slow speeds, then warn again as airspeed increases... brilliant.

I am not a fan of autotrim in the 777 either.

Not exactly the case. The flight crew were two XL line pilots asked to do an Alpha Protections test without full knowledge of how the aircraft would behave as it approached the stall. The test should have been carried out at above FL100 but commercial pressure resulted in the test being undertaken without ATC knowledge while being vectored on approach at about FL030. The third seat was occupied by the AirNZ check pilot tasked with overseeing the end of lease handover by XL to AirNZ.

A full read of the report will reveal all.

A lot of interesting reading and theories.

A quick and incomplete look at some stall accidents still bothers me.

Birgenair 757 stalled due to pitot problems and the pilots not proficient enough to recover, although the aircraft would have permitted. Reasons known and uncontested.

Cali AA 757 stalled due to the non self retracting speedbrakes and the pilots not realizing it. The aircraft would have permitted recovery. Reasons known and uncontested.

330 testflight in Toulouse stalled due to pilot mishandling leading to an unrecoverable stall. Two experienced pilots. Still some debate if the aircraft would have been able to save, still debates about the electronics/protections handling.

320 Perpignan stalled due to THS behavior. Normal pilots. Still some debate about the recovery possibility or not.

Qantas Perth. Aircraft apparently didn't obey pilot orders, recovery succeeded. Still debating about the real reason of the electronic/protections behavior.

AF 447. Enormous debate about the THS, crew performance. Unsure if the aircraft was recoverable.

The troubling questions are still looming, and they are all on AB.
Boeings might fail just as much, but it seems that they would be more easily recoverable in upsets. I can't dismiss the ugly feeling that in upsets the possibilities in AB are less and it would take almost IT trained astronauts to be able to realize and apply the multiple tasks, switchings or many and different procedures to recover.

Airbus needs to clean up their act. Even Joe bloggs like me should be able to apply and memorize a simple and uncomplicated task for upset recovery.
At the moment this seems unrealistic. Therefore all debates are basically futile, because any finding will lead to the perpetual "they should have known" which seems almost impossible.

Gretchenfrage

Where did you get this misinformation from? if it is the crash I think you were talking about they were simulating and engine failure and the due to a problem with Alt* the aircraft lost too much speed, they had almost recovered but did not have enough height. The Alt* programme was subsequently changed. More of a Vmca problem.

Again misinformation! The THS was a contributing factor, the pilots incorrectly carried out the low speed check at too low an altitude and without following the Flt Test procedure. A recovery could have been possible if the correct actions were taken / correct procedures followed.

Jury still out on that one, as the equipment tested correctly and there were other factors.

There is no enormous debate about the THS, it behaved correctly and if the correct actions had been taken I am sure the A/C would have been recoverable.

What an amazing statement to make! Perhaps you are not an average Joe Bloggs!:rolleyes:

Finally, some useful and relevant discussion on this thread during these last two pages.

The Perpignan Accident may well explain why the crew were unable to recover flight AF447.

However it doesn't explain the F/O's actions in response to the unreliable airpseed.

Was it...

A) He was applying (inappropriately) his memory items practised recently in the sim?

B) An attempt to "regain" altitude apparently lost during the event?

C) An attempt to climb above the weather they were experiencing i.e. turbulence, hail, st elmo's fire?

@SKS777Flyer

the 777 only auto trims for config changes as you know. It doesn't speed trim which is still a manual input.
May I ask why you are not a fan of this trim setup?
The only thing I have with the system is that there is no trim wheel so you are not very aware of what position the stab is at.

I think the THS has played a massive part in this incident but there is not enough information to deduce exactly what happened. A lack of visual cues I've always had issues with. It relies on an active scan (even in cruise) which as we all know is not something a human being is very good at in states of low physical demand. Combine that with a lack of training (cost/sim limitations) in unusual situation and we can see the holes in the cheese lining up.

Having had TAT probe icing in the cruise (without knowing what to look for!!) we thought it was static around the EECs that was causing the EPR indications and all Perf calcs in the FMC to blank (Also A/T disconnect) therefore never did the QRH drill.

Lesson learned...

The Duh in Aerodynamics
 

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, Fright 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 Langewieche'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.

Hi,

Just a tought ... but for me if the tests were conducted at the altitude of 35.000 feet ... the result of Perpignan will be the same than AF447
I don't see that altitude will change the fate of the Perpignan event.
The scenario was set to finish in the sea .. from any altitude over the one of the day.
And indeed the pilots were very experimented on type.
Again .. the hours on type are not a reference for "experience" ... as seen in many accidents.

The memory items were innapropriate (reason why AF changed it after the AF447 crash and sended all their "experienced" pilots to the sim for play again the scenario)

I DON'T BELIEVE THIS..
Are you serious?...:ugh::ugh::ugh::ugh:

We are talking about jets here, it's the other way 'round

(And that makes it adamantly clear: you never flew one)

Its not "black and white", golfyankeesierra, it really depends on the circumstances: for example, when you're on an "open climb" in your A330 (at a fixed power), its pitch/attitude that controls your speed. The same for an open descent.
After more than 1600 posts here, where the main preoccupation was to understand why the AF447 PF didn't lower the nose of its A330 to reduce AoA and therefore to increase "speed", it seems pretty clear that not always "power" is enough to regain speed...

iceman you just proved my point.

QED

golfyahnkeesierra makes it plain why modern "airmen" sometimes know nothing about airmanship. Just because his electric airplane's power levers stay in the climb detent, he thinks "You pull back to go up and push forward to go down."

I'd rather fly with Wolfgang Langeweische (or his son William, which I have done) than GYS.

Pearpignan

Golf X-ray Lima triple eight
Tango contact tower one one eight decimal three bye
End of stall warning
Single chime
15 h 45 min 54 What’s wrong here
15 h 45 min 55 Flaps up
15 h 45 min 57 (*)
15 h 45 min 58 Flaps up
15 h 46 min 00 End of stall warning
15 h 46 min 00,5(*)
Continuous repetitive chime
15 h 46 min 02 Speedbrakes
15 h 46 min 02,5 End of CRC
15 h 46 min 03 C chord (Altitude alert)
15 h 46 min 04
SV: (*) terrain terrain
15 h 46 min 05 (…) (…)
15 h 46 min 06
15 h 46 min 07 End of recording

Someone unstalled the a/c. Unfortunately, it was pointed at the Ocean. Either the pilots started the Drill too low? (or not). Or the a/c would not allow NU? (what do the g traces say?). Both?

GYS I presume you are a Flight Sim wannabee if you don't understand how we can control airspeed with pitch (which you do everyday on an airliner, well any aircraft, in both climb and descent) :{

I am an aircraft engineer with nearly two decades of experience in the industry. I am not a pilot. What I find SHOCKING is that many professional pilots in this thread disagree so strongly on such basic issues as flight dynamics or what a variation of throttle will do to you in level flight. This is really scary. I know quite a lot about airframe design as well as flight control system design having done both for many years. But this thread is proving that as automation proceeds flying IS going to become more and more dangerous. And if that were not enough, they've now started to make airplanes from plastic!

Hi,

If you find G traces in the BEA report .. you lucky man
Myself found nothing about G traces in the BEA report.

jcjeant

No traces of gee? How is that possible? Is the report available through the FAA? I can't imagine not, the A320 is everywhere over here.

complexman

As to resin, 447 had few composites in structural places. If it actually did, please don't tell me. As one who has designed and built in composites for ~40 years, I am most apprehensive about two things. Elasticity, and Fire.

Airbus has the obsession to use composites in much of the tail in most of its models. Joining a metallic component with a composite one is like asking for trouble. Always. (e.g. see section 19 on the A380). But that is not what is worrying me - I am scared of the 787. Rumors indicate that it actually would be lighter had it been built of Al instead of composite. This is because composite have never been used on such scale before so large safety margins are used to absorb the uncertainty.

NOD, stepwilk, aguadalte,
I was reacting to above statements

Yes, in a climb or descent pitch=speed, but then power becomes rate

But otherwise:
In a prop: pitch=speed, power=altitude
In a jet: pitch=altitude, power=speed

When you fly an ILS and you get a little high, you don't pull the power, you put your nose down.

What I am objecting to is GB's notion that the 2 mentioned accident are attributed to this pitch/power thing, and what I object most to is his "advice":

Now back to the AF447 and all this discussion about the stall recovery "procedure".
Stalls aren't trained anymore, they are such basic flying skills that the only time you do them is as mandatory items during type conversions,
but on every type conversion from the very beginning of my flying career they are (with the exception of the option of flapextension on some types) the same: lower your nose (on the horizon will do most of the time) and put on some power and you're out of it.


I can't believe that a pilot with the experience that equals the AF447 least experienced pilot consciously counteracts a stall with pitch-up command.
The big issue here is what the pilots felt and saw, and the BEA statements are a bit puzzling here.
I don't understand the sequence of AP and ATS dropping of before the airspeed indications became faulty. You only get alternate law after ADC's become unrelaible but the aircraft was already in alternate law before the speed dropped from 275kts to 60.
I don't understand the low speeds; I would expect speed increasing with altitude with blocked pitots.
I also don't understand the pilots perseverence in maintaining pitchup command; in his situation I could understand a temporary wrong input, but why so long?
Personaly I think the BEA has not given the full picture regarding actual flight laws; I am also afraid some unknown pitch protection feature played a role, pulling the nose up, while we are thinking it was the pilots doing...

Anyway the pilots were most likely overloaded, spatially disoriented and fooled by their indications, as we all would be.

I don't think an industry wide change of flying technique "Pitch equals speed", as GB suggests, would have saved the day here.
And as much as I like to be a "hands on" pilot, I think the prevention of this happening again will be a technical/engineering solution and not a piloting skill.

BTW, no, I am not a FS wannabe

golfyankeesierra

I more or less resent the ease with which pilots are doubted, and the fall back is "It did what it is programmed to do". Fine, perhaps because pilots can think and
innovate, there is some residual resentment that programming gets a look once in a while. For what it's worth, any discussion should have some (alot) of room to wander, we're stuck with fbw. Not that it is poor, it is fine, but it gets this knee jerk defense where professionals get the magnifying glass.

So be it. My baseline is that this crew were eminently qualified, and perhaps more so than the bus. If there is a fault, it may be (probably) that the orchestra hit some sour notes, whether flute or conductor, no matter. The deal is that not enough practice leads to "Prior Planning Prevents Piss Poor Performance". Will the Bus surprise? It is certain, for there is simply no way this crew flew to STALL without some mitigating events. I think this should continue, for it is only the pressure of the folks that will goad the sloth.

Bear, not doubting the pilots, nor the plane.
I think the 'bus is as safe as any other plane, probably even more.
But I do think there will be some "discoveries" in the course of the investigations revealing a) new notions in passing through weather in that particular area of equatorial Atlantic, and b) new insights in the A330's FBW system.

BTW, remember the Lufthansa A320 tipstrike at Hamburg? In the course of that investigation it showed that most pilots were unware of a specific behavior in the roll-authority at touchdown:
BFU report page 62

I guess the AF447 final investigation report will spit out similar words..

Iceman(appropiate enough),

So you dont think autotrim will feature in the report then?You're quite confident that the automatic application of full ANU tim followed by auto-cutout is a good example of "fail-safe" design?And that the transition from auto to manual (when how why it occurs) is intuitively understood by the poor pilot?So why perpignan and now AF?or the tarom or taipei?
It behaved correctly?It behaved as designed.

You might think your oh-so-clever destruction of Gretchenfrage's points were on the nose but you forget one thing;those planes crashed and Im afraid the pilots didnt really know why they were crashing.THEY DIDNT UNDERSTAND WHAT THEY HAD/HADNT DONE.If a design is ambiguous,then it is deficient.

Do you have anything to say about the stall warning inhibit?Id love to hear your thoughts on this one.Over to you ace.:mad:

Hi,

In alternate law with auto-throttle off :confused:(read BEA note !)

Hi,

A little of topic but an interesting table ....
By the ACARS ... the BEA ?? .. and many people of this forum had concluded that the plane was falling rapidly (a stall or spin condition)
So (I already commented) I still puzzled with the management of the researches by the BEA (almost two years spend in thin air ..)

http://i.imgur.com/BI6Ml.png

It used to be said that the only really silly question is the one you don't ask.

I'm wondering WHY the autotrim 'decided,' in both accidents, to go to 'THS full up' in the first place? And then STAY there, even though both pilots were in the end pushing the stick forward? Anyone know what the 'system logic' that could cause that reaction is?

The BEA gives us no guidance at all on the point. For the Perpignan accident - even though it's the final report - the BEA just says:-

In the case of AF447, it says even less - it just tells us 'what' happened, and doesn't even tell us when it happened (i.e. which minute):-

No mention of 'why?' in either case.

So here's my 'silly question.' Despite the fact that the autopilot and autothrust had 'signed off' on AF447, and the pilot at Perpignan was most certainly seeking to get the nose down all the time, and the AF447 one much of the time - is it possible that the autotrim in both cases was still trying to regain the previously-commanded altitude?

Never flown anything with autotrim (in fact, I've only flown anything with an autopilot twice in my life). But as far as I know, that (keeping the aeroplane exactly to a given altitude) is the main 'everyday' function of an autotrim?

Flying Basics, straight and level:
Pitch attitude controls altitude
thrust controls airspeed
This for prop, jet, rocket any type of propulsion in fixed wing aircraft, but only on the front, right side of the thrust versus speed curve.

Left side of the curve- opposite. This because of negative speed stability, where a given power setting doesn't have one but two correct speeds, and the aircraft would always fly away from the desired speed on the left side..

BEA published facts found, not conclusions, that is why no reason given for AF447.

So why no reason for the 2008 A320 accident at Perpignan either, opherben?

In the final report?

GYS

Disagree... ;) If you can show me a training manual clearly stating the opposite, please post it here, but for now I will extract from the Student Guide to my first Jet:

http://www.aghsoftware.com/PrecApp.jpg (This is actually for the PAR, but the same technique used for an ILS).

In practice either technique works to an extent, but the 2 are intertwined.

NoD

Keep it simple:

Pitch attitude IS speed control: :8
On a glider you adjust your speed with your pitch attitude.
On a 747 without any thrust you have a veeery big glider:O. Again you adjust your speed with your pitch attitude.:ok: (Altitude is "just" a time factor:sad:)

The bonus by power/thrust: You are now able to maintain your altitude - even climb (in most situations:}) So power/thrust IS altitude control!!!:ok:

By the way - ain't we just a little of topic??:\

complexman:complexman:
We have a saying in my country, that goes like this:
"Presunção e água benta, cada um toma a que quer..."
(Presumption and holy water, each one takes whatever...)

What I find really scary is the way engineers are designing flying machines that are so complex that even made them think that they have created an aircraft "against pilot's mistakes".
Man/machine interface was relegated to a status of "get used to it". Adapt yourself to your new role: flight management.
Fortunately for us, things are not all black and white. Engineers are not perfect, nor are we pilots...
But one thing is for sure, pilots are open to debate, open to new ideas, open to other professional classe's meddling and scrutinizing opinions.
In favor of flight safety, we do need to continue to open ourselves to our own scrutiny and open ourselves to other's opinions. I have learned a lot in this forum. There are a lot of great professionals with whom I love to exchange ideas and comments.
What we don't need is that sort of sleaze and arrogance, especially when coming from someone who should behave as an invited guest and therefore adopt more urban manners.

Quote, "With the greatest respect to some: On Approach,

1) light aircraft use pitch for speed

2) Heavy Jets use thrust for speed

Too many light aircraft pilots here who obviously have no experience in heavy aircraft operations "


By George,
I beg to differ. Since you are on the thrust curve backside, adding thrust will not necessarily regain target airspeed, but lowering attitude will. No different from light aircraft.

The differentiation of light from heavy aircraft flying technique is an error in understanding aircraft flight mechanics and resulting handling qualities, even if the chief flight instructor taught this way. What matters are design parameters like wing loading, thrust over weight, lift over drag, and the CL vs Alpha and thrust vs airpseed curves. The B747 at any landing weight isn't substantially different in approach handling qualities from a Cessna 206, even though the Boeing wing is swept, and has more tires and Lbs. Their greatest handling qualities differences are in the flight control system mechanical characteristics, irrelevant to the above quoted issue.
The writer served as chief experimental test pilot since the 70's.

Hi,

Pitch and attitude ....

For those questioning the auto-trim on the airbus - this is a function of the FBW system.

On a conventional aeroplane (PA28 or 737) the pilot pitches up using the control column and manually trims the pressure off using the trim wheel or electric trim switch (same thing).

On the airbus this happens automatically. The pilot pitches the aeroplane up with sidestick inputs and the computer trims off the resulting "pressure" (you can still see the trim wheel rotating back during this process).

If the pilot applies sufficient back stick for a sufficient amount of time then the trim will wind fully back to the stop. This is what happened during the deceleration phase of the Perpignan Accident and almost certainly what happened during the Air France 447 tragedy.

In some conditions the auto-trim disconnects (abnormal attitude and direct law) and the trim setting and therefore wheel and stabiliser will remain in that final position until either

a) auto-trim is restored

or

b) the pilot moves the trim wheel manually!