fyrefli

(is the bit immediately before...)

This was discussed in the first thread very shortly after the accident.

As was pointed out at the time, 20kt is only 10m/s. I say "only", as many glider pilots will be familiar with benign - if somewhat exciting under a paraglider! - climbs of this type at low levels. On a decent, post-cold frontal day in the UK - not exactly known for the relative strength of its thermals - it would be disappointing not to get climbs of 5m/s under small, perfectly benign, 10 minutes later they're gone, fluffy little white cumulus clouds. If "updrafts are usually strongest in the upper troposphere compared to lower levels", then 20 to 40kt seems quite a conservative estimate.

It would surprise me - and I suspect most glider pilots - if you could find any self-respecting cumulonimbus that *didn't* contain updrafts of at least 20kt.

EDIT: Note that I am *not* arguing that a strong updraft caused the zoom climb or had any other bearing on AF447, merely re-iterating, for the benefit of latecomers, comments made a long, long time ago on the above analysis.

HazelNuts39

There is evidence of turbulence - I think it caused the "stall warning twice in a row" shortly after 2:10:05. There is evidence of the absence of a strong, sustained updraft that "pushed" the airplane up to FL380 before 2:11:06 - see below.
Precisely. A strong, sustained updraft would have been evident as an increase of the total energy of the airplane. On the contrary, there was a slight decay of total energy up to the point where the airplane stalled. Another poster on this thread has correctly explained that decay as the result of thrust reducing with altitude and increased drag due to manoeuvering airloads.
Not so. The gain in altitude is entirely consistent with the loss in airspeed, except for the decay discussed above.
Agreed, and on the AoA trace, and also small-scale turbulence would appear as "grass" on those traces, provided the sampling rate is high enough. These can be separated from changes due to control inputs by looking at the traces of elevator and THS position, and sidestick positions.
If you are referring to my reply to BOAC, I didn't say that the FCS filters loads. I was referring to signal conditioning that suppresses high-frequency content of, e.g., the AoA signal, before it is passed on to the consumers.

Lonewolf_50

Thanks for your reply.

I wasn't referencing your reply to BOAC on the matter of filtering out the loads imposed on the airfoils by factors outside the flight control system (Turbulence, etectera).

I was more of less "thinking aloud" based on some of the block diagrams of the flight control system, and considering how the installed stability functions (In normal or alt laws) would first sense, and then account for inputs to the system from outside the aircraft, as opposed to adjusting for inputs from within the control system.

DJ77: thank you. Re-reading that got the point across.

Caveat: the assumption that the air mass data (airspeed/Mach) were not already beginning to degrade by that point, but it seems a safe assumption based on when alerts and miscompares show up on the record.

SDFlyer

HN39: "The other illogical element in my view is that alpha-prot law is not cancelled when AoA decreases below alpha-prot. Again I suspect that that choice has been made after intensive investigation of all the "what if"-s, but you have to ask the designers."

Perhaps it is a naive question, but why is there not more information available (public domain) about the choices made by the system designers, so that certain excellent questions raised by HN39 and others can be better addressed? I understand that there may be proprietary matters at stake but in other industries, such as my own, critical safety-related matters are fairly openly disclosed/discussed. The regulators enforce it, for one thing. Is there no technical journal in which such matters can be presented and discussed? If there is such a journal, is it serving this purpose to the full?

Anyway, I'd like to thank HN39 and others for so patiently and clearly explaining their thoughts on the matter - I speak for many who are learning a lot about Airbus detection and control systems in this thread.

Please carry on.

grity

"AAIB Bulletin No: 6/2001: Consequently, in turbulence the speed scale will probably be oscillating, the aircraft pitch angle could also be oscillating..."

if the bird flow for sume time nearly in a balistic curve, the AoA vane is in a stable normal position... no AoA protection will start working

AoA protection alone seems not very good for stable flight

the climb-input is interesting, after the stopp of the autopilot they moved the elevator up to +4 for ten sec. but in the following seconds the G falls to 0.5 and the pitch drops a little down (!) IMO this needs good downwind. then they hold the elevator between 0 and -3 and pushed the 4 engines this must be the climb-input, mayby together with the autotrim

ar you shure AoA reached alpha max? nighter the trim nor the AoA is shown in the diagram. the climb after the startinput could also happen with a lower AoA....

DozyWannabe

@SDFlyer - There are plenty of links in this thread and the previous ones to Airbus documents that describe the various systems and mode reversions, along with the logic that triggers the latter.

Am at work now, so can't hunt them down myself, but they're there. I think the one you're looking for would be called "Airbus Control Laws".

HarryMann

That whole statement seems to imply a much wider bandwidth and shorter time constant for a mechanical AoA sensor than ever likely. Also implies that anyone would be interested in small scale high frequency turbulence... that would be for a hot-wire anemometric device if we're into the business of looking at 'gustiness', which I'm pretty sure we aren't

infrequentflyer789

I don't think anyone is suggesting that.

Transient overspeed in turbulence prompted the crew to close the throttles.

As speed reduced, turbulence then caused transient increase of alpha to exceed alpha-prot (or the predicted trend to exceed it), this engaged the alpha flight mode such that the neutral sidestick would command alpha-prot (and fully back, alpha-max).

If this is activated by a transient high alpha value, then when that transient effect goes away, you will get a climb. Alpha-floor then probably kicks in to increase the thrust after the pitch up.

Ah, but under what circumstances ? Like all safety engineering, in some situations this feature will do the wrong thing (in others it can save you). Sometimes the only survivors are those thrown clear, sometimes it's only those who are belted in - so should we have seatbelts or not ?

Maybe this law should never activate in turbulence in cruise, but on the other hand if it had activated on 447 (which it didn't because normal law had been lost) then it would probably have avoided the stall. Or consider if the A340 crew in this case had been the ones to get "climb climb..." from TCAS

Graybeard

At the weekly Old Bold Pilots breakfast this morning, I asked the guy who was cognizant engineer on the stall warning computers for the DC-9 and MD-80. He was incredulous that the A330 Stall Warning would shut off below 60 knots airspeed. He said the AOA vanes on his planes would measure to about 50 degrees AOA.

I suspect the A330 vane mechanical limit is about 30 degrees, as I don't recall any greater AOA mentioned by BEA. Does anybody know?

henra

There is a much stronger argument against updraft and that is energy conservation.

Decreasing speed from 275kts to 215kts IAS at the apogee equals roughly 4100 feet altitude gain from an equal energy perspective.
Taking into account that there are some drag losses due to g load and roll the 3000 ft climb match excellently to the altitude gain to be expected by trading speed for energy based on the given data points.

Had there been an updraft the energy level at the apogee would have been higher.

BOAC

Ah well. You see what you see, I guess.

"If this is activated by a transient high alpha value, then when that transient effect goes away, you will get a climb. Alpha-floor then probably kicks in to increase the thrust after the pitch up." - That's really clever - when you inadvertently pitch too much, the system ensures you stay pitched too much. A climb no-one wants or needs - thanks AB!

God help us all.

Lonewolf_50

As noted above, it's a compelling argument providing the IAS information we are working with is accurate. Given "ordered" airspeed and "what it takes to stall" the measurement anomalies seem to wash out.

@BOAC, in re God help us all ...

Doesn't this take us back to why you must have humans on the flight deck and in command? The PIC must be in a position to override discrepant subsystems.

Systems will go squirrely.

That said, I agree with you that this particular feature might profit from some rethinking. Having read what you responded to, it makes no sense to me for this feature to be enabled at high altitude cruise. The feature appears to be primarily designed for flight regimes near to the ground.

galaxy flyer

Now, I am all in favor of FBW; it simplifies systems; saves weight, and increases efficiency. But, why did the engineers not just make it fly last the last 100 years of aviation. Speed stable (trim for a speed), back-driven so the pilots know what is happening with the stick and rudder, no obscure modes that are confusing in an emergency.

Oh, Boeing did that!

RR_NDB

GF, Hi






The "features" sometimes creates problems. Who will change that?

The "problems embedded in the features" could be eliminated?

It´s possible to identify it in the design? Could be testable?

A33Zab

- Operating Range 120º, limited by fixed stops.
- Balanced (= static it could take any position).
- Contains a dual purpose damping motor, damping the rotor in opposite direction of movement
created by Eddy Currents with a torque proportional to the speed of rotor movement, with a breakout force of 0.04 Nm.
- Damping motor can also be used on GND for test purposes (positions AOA sensor in a pre-determined test position)
- Internal heating element 115 VAC, 400 Hz; operating temp. 120ºC.


LINK

fantom

BOAC is a really good chap but, unfortunately, has not enjoyed an Airbus type rating course.

He will soon I'm sure but, in the meantime, let us forgive his neandethal mutterings.

sorry mate.

jcjeant

Hi,

It's no doubt (for pilots and general public) that the Airbus airliners are very sophisticated aircrafts stuffed with modern technology materials
Now .. the question is ..
Sophistication = simplification ?
If the answer is NO
Why it's seem's that many airlines have not very sophisticated programs of formations (schooling) and high training for their pilots ?
How it can be that a general opinion is that in general the training and formation are on the down slide .. and in the same time .. the aircrafts are on the up slide of sophistication ?
And what is the response of the officials bodies for this ? (regulators .. laws makers ... etc ..)
It is now the aircraft industry corporates and banks who are regulating the air transport ?

CONF iture

Sorry but, in that perspective, a type rating course won't teach much. Only regular, repetitive, and studious incident/accident report readings can help to realize that nothing is that simple in the Airbus world. Every report brings its part of discovery ...
This is not only true for the pilot, but probably also for the designer himself ...

Do you know how the 120 deg are distributed, is it +90 -30 ?

CogSim

Software Engineers will tell you its Abstraction. You don't need to know how the transmission works to drive to work everyday.

The bean counters will tell you its statistics. How many times have you trained for brakes in you car giving out at 60+ mph on the highway?

Ironically, "Simplicity is the ultimate sophistication" was an early slogan for Apple Computers.

DozyWannabe

Because at some point the training wheels have to come off. If everything was made to work "just like the old days" this board would be a complete pig to use!

Put another way, Boeing made the 777 to simulate a feel similar to that which Tex Johnson had in the Dash-38. Airbus made the A320 FBW series to feel similar to the equipment the Apollo astronauts used to land on the moon. The methods are *different*. Not better, not worse, but *different*.

I don't understand what's so confusing about "if in Normal Law rely on the protections, otherwise do not and apply more caution when making control inputs". We don't even know if all this round-the-houses about what does what in which law applies in this case anyway. We know the pilots were aware they were in Alternate Law and we know that the PF made some control inputs that on the face of it make no sense. All we don't know is why - but it seems a select group have already decided it must be the computers' fault, despite the fact that they have no more information than those who are advising "wait and see".

What has Software Engineering got to do with whether someone knows how the transmission/gearbox (for us Brits) on their car works? I guarantee you that the majority of drivers wouldn't have a clue (and I only know in general terms). Furthermore, abstraction is something that has happened in aviation ever since someone hooked a pitot up to a pneumatically-driven dial. That dial was abstracting the raw information from the pitot tube via a mechanism that translated that into human-readable form. Some of those mechanisms were very much better than others!

Aside from the fact that, as I've said countless times, the software that runs on aircraft is only a gnat's chuff comparable to what you and I use on our PCs every day, personally I've always considered Apple guilty of what the naysayers here are saying about Airbus - i.e. deliberately obfuscating the workings of the system - in their case to enforce dependency on their retail chain to fix problems.

The difference is that it takes a far lower grade of technician/systems administrator/software engineer (i.e. me) to understand what's going on in a PC or server (which - let's face it - these days is usually a PC) than it does a safety-critical real-time system like those plumbed into aircraft.