re airtren to lone - I think the word you're looking for to replace "lack" in "lack of lift" is "insufficient". As a matter of fact that is how I interpreted lone's comment.

By the way, what does the water bottle tell you that the pitch display does not? So far as I know that, at least, was still working.

funfly, you can be falling at mach 20 and not feel it. All you can feel in your ears or your body is a CHANGE in velocity. And there is no known body that, in air, continues to accelerate all the way down from 38000'.

Yeah, I'm picky that way. Please excuse.

True Air Speed vs other air speeds
 

This graph does not show the velocity of the aircraft. It shows Corrected Air Speed (I think). True Air Speed would be a decent approximation for the velocity but CAS is not anywhere near at the altitudes involved here.

Can the meme that some hand of god is necessary to explain the zoom climb please go away. It has been demonstrated many times that there is about the right amount of energy available including an allowance for manuoevering losses.:ugh:

Ooh! Just been buzzed, well at 2,000ft, by the Dragon Rapide (from Duxford I believe). Way cool.

takata commented to A33Zab about the IR data.

Regardless of the IR data from ADIRU the ISIS data existed. And enough data was recorded that the BEA was able to follow altitude and attitude of the plane all the way down. What makes anybody think ISIS data was not presented in the cockpit?

If it wasn't ABI ought to be totally pilloried, if they did not make it available, or AF should be excoriated if they skipped over this as an "unnecessary frill option."

Mr Optimistic, "I though the 0.5*(v1^2-v2^2)=gh equation had been looked at earlier and found to be broadly consistent ?"

It was - with a speed at the apex of 215 kts, 240 kts maybe....

Mr O
Indeed - I am a night owl. And I thought I left room in there for cabin pressure sensing in the ears. But the inner ears don't feel even pretty extreme pressure changes unless you've had surgery that exposes the area by drilling through nice thick bone. All the inner ear senses is tilt and acceleration. And those can get mixed up very easily in a dark room.

I've said too much already but there is an observation I'd like to make.

Here is a simple sentence. "Our speed is 215 kts." This is in English. If I say it with flat or even feminine with the slight upward lilt at the end it means exactly what it says, the speed is in fact 215 kts. It's a statement of fact. If the pitch change at the end of that short sentence is made to sound like a question it is a combination question and statement of incredulity that the speed is 215 kts, "Our speed is 215 kts? (How in (censored) can that be?)" when the unstated part in parenthesis is included.

French adds handwaving to the picture. There's no way we're going to guess precisely what was said dissecting the words given us. And, as noted, even hearing the recordings won't necessarily help much.

Is there a better topic to be entertained about?

jimjim - accounted for - the energy loss work I did ran from the mach numbers translated back to speeds based on the speed of sound - an approximation. It appears to be about a factor of 2 give or take a bit for the correction.

There is no such thing as FPV ECAMs fault

That's not supported by the traces as posted by A33Zab, something else but what ?

takata, you don't seem interested to address your notion of normality ...
There is a clear internal conflict in the selected vertical speed as there is also one in the selected Mach ... What is it all about ?

Hi JD-EE,
Re: "Then the PF on AF447 was not a pilot?"

I think you missed the part where I said, "but since recent events have shown us such pilots do exist..."
Of course he was a pilot. Saying I can't imagine it isn't the same thing as saying it can't be.

I've said many times I think these poor folks were in a heck of an ugly situation. One might call it 'the perfect storm' to challenge his abilities... But he was a product of his training. Clearly, we're learning that many pilots don't know how their machine will behave when stalled. In my mind, that points to a serious deficiency in their training. I think it's akin to not knowing how the machine will behave with an engine out.

I suspect it's an inevitable result of the "cost effective risk management" biz... 'Creating a sim that can teach stall behaviour would cost too much and the aircraft are unlikely to stall anyway, so we won't bother.'

Which brings a question to mind... Somewhere I recall seeing a training aircraft (might have been a helicopter?) that had been designed with the ability to emulate the behaviour of multiple aircraft, depending how it was programmed.... Could such a system, in a small aircraft, be utilized to teach the stall behaviour of transport aircraft, I wonder?

I recall seeing the same, although I no longer remember what the aircraft type was.

Howver.... the problem is the same as the sim: if you don't have accurate data for the behaviour of an aircraft well into the stall, there is no way you can program either your sim or your 'training aircraft'.

Not A helicopter - a converted C131 by Arvin Calspan.

Calspan Retires USAF's Last C-131

Autotrim
 

Autotrim is useful in ensuring that the aircraft remains trimmed when in autopilot so that when the autopilot is disconnected, either by the flight control system or by the pilot, he is not dumped into an out-of-trim situation. However, as I have said several times before, when I am hand-flying, I don’t want the system changing the trim. I want to do that myself. Trimming is not an arduous task. In fact, it is a completely natural act and it is second nature to a properly trained pilot. It would be even easier if the AB side sticks were equipped with “coolie hat” switches. That is my personal opinion as a pilot. You have told us that you are not a pilot so I believe that you have little basis for an opinion as to how you would want to fly an airplane. Apparently you are qualified to offer opinions on how software should be written to meet certain criteria specified by the users (the pilots), but it is those users who are best qualified to set the criteria in the first place. You have stated that there are good and sufficient reasons for the design of the software in the hand-flying mode, but AFAIK you have not offered any reasons why that design is preferable to my reasons for disconnecting autotrim when hand-flying. As a user, I believe that my preferences should take precedence over yours. I am open to reasoned arguments on that subject.


That’s your opinion as a non-pilot. It seems to be the consensus on this forum that the pilots of AF447 were not taught properly. It is my opinion, as a pilot, that because the autotrim continued to follow the inexplicable nose-up inputs by the PF, stall recovery would have been made more difficult, had they ever attempted stall recovery.


I fully agree that the full nose-up trim situation was the direct result of the inexplicable nose-up inputs, but you need to understand the proper technique for hand-flying in turbulence, a technique which has stood the test of time over many decades. As I have previously posted, the technique for flying in turbulence is to first be properly trimmed before entering the turbulence and not to change the trim, allowing the aircraft’s designed positive longitudinal stability to keep you flying properly. That is essentially what the stated procedure is all about: “Fly pitch and power”. Presumably, AF447 was properly trimmed and the power properly set before the autopilot and autothrottle dropped out so they really didn’t need to do anything except take a deep breath and monitor what proper pitch and power was doing for them. If the dynamics of the weather take you off the desired altitude, you simply make small inputs to return to that altitude but you don’t change the trim because you want that proper trim setting to help you minimize excursions from the desired flight parameters. If, as a non-pilot, you think you have a better technique for flying in turbulence, please post that on the forum for the pilots here to consider.

Sometime back, someone here offered that the pilots of AF447 only needed to let go of the controls and the aircraft would have returned to normal flight on its own. While that is true with conventional flight control systems and a properly trimmed aircraft (for cruise), it was not true with AF447 because the autotrim had changed the pitch trim from a stable, level-flight setting. With a century of manned flight under our belts, the consensus of pilots is that aircraft should exhibit positive longitudinal stability. But the AirBus flight control system changes that, overrides the natural aerodynamic stability of the airframe and introduces neutral longitudinal stability when hand-flying. As a result, when a pilot moves the stick in pitch, the nose stays right there and will stay there even if the pilot lets go. It is my opinion as a pilot that an aircraft that exhibits neutral longitudinal stability is more difficult to fly properly than with positive longitudinal stability. If you have a different opinion, it will have to be as a non-pilot.

It is my opinion that the pilots of AF447 were so poorly trained that they really didn’t know what had happened to the trim. For AB pilots, trim seems to be out of their notice in any situation except takeoff where they set it and forget it. Actually I believe that even if the AF447 pilots had known what had happened to the pitch trim, they would not have understood the consequences. They clearly didn’t understand much about flying an aircraft.

Dozy, it you have relevant arguments on why autotrim should not drop out with the autopilot, I will be glad to consider them.

There are other subjects which would be appropriate for separate threads such as the lack of tactile feedback in the side sticks, and whether or not it is appropriate to use the autopilot in heavy turbulence. I did not bring these up at this point because I wanted only to address your opposition to having the autotrim drop out when the autopilot drops out.

A flying variable stability testbed for recent posts by 3HL & CJ ?
 

2011: Edwards AFB test pilot school has a variable stability F-16.

It is a one-of-a-kind VISTA (Variable stability In-flight Simulator Test Aircraft).

The VISTA can be configured to fly and behave like any aircraft, from a UAV to a C-17 Globemaster. It also has enhanced data recording capabilities.

Article at TPS's Test Management Program brings real-world projects to classroom

Well said, Smilin_Ed! Being a know-all is so endemic in the computer world that it's refreshing to hear the other side put the foot down.

curvedsky,
Many thanks for that very interesting link.

And no, it was not an F-16 I was remembering, more like a large twin jet. Might have been a DC-9, a 737, or a large business jet.

Slightly O/T, but IIRC NASA has a few T-38s that can be reconfigured to "fly like a space shuttle" and that the shuttle pilots used to "stay current" and practise the approach.

Maybe they're for sale now?

http://www.pprune.org/rumours-news/4...ml#post6623524
Know the aircraft you are flying ... it's help in some situations ....

Hi Smilin Ed
 

You are far too gracious. I won't belabor this, and won't stay, but this needs to be writtern.

Since the few days after the crash, a few PILOTS have noted the problem w/trim in Alternate Law.

Each time the THS moves, The airframe starts behaving like a different a/c. One reason I think the PILOT had problems with PITCH is at least because this ship did not want to lower her nose. Besides, when he did attempt it, He needed WAY MORE ND than he was comfortable with. WHY? because, as DOZY WANNABE has said... "The THS COMPENSATES for the elevator position". Go look up compensate, and think about if you would like to have a massive set of wings ON THE TAIL, "taking away" your elevators..... AUTOMATICALLY, and without any prompt on the Flight Deck.......

English BEA #3, Page 111, t>=02:11:00

Locate the 4 lines conveniently next to each other.
brick read, purple, cyan and green.

(brick-red line) look at PF nose downs (+ve above zero),
(purple) elevator max deflection down (forcing nose up)
(cyan) because the THS is auto trimming.
(green) the pitch stays nose up,

Example
t=02:12:17
stick 2/3 (10/16) forward deflection.
elevator -30 deg
THS -13 deg
pitch +4 deg.

My point is that the a/c sometimes did the opposite of inputs (pitch up with stick forward and pitch down with stick back). This was because a/c was dancing around edge of the stall from the outside of the flight envelope.
I stated this because someone said that you could just fly it by behaviour. The behaviour was terrible i.e. inconsistent and at times contrary to stick inputs. A/c needed to be flown by pitch and power with manual THS trim not by its behaviour.
Another point to make is that the instruments were impared, e.g. IAS, altitude etc. The true air speed and true altitude could have been different as noted by the QF72 incidents CPT.

Fair enough, that's your opinion - but have you ever actually flown a FBW Airbus? Plenty that have state that the autotrim is completely unobtrusive when hand-flying and that the aircraft as a whole handles rather well.

In fact I did, but it's several threads back - one of the reasons was the ability to have hands on throttle and stick in a pilot incapacitation scenario.

And it is my opinion that had the pilots been taught how to use the manual trim wheel then they would have had an option for correcting the position it ended up in due to the overcontrolling that occurred just after FMC disconnect. Of course, more fundamentally than that had they been taught how to handle the aircraft properly manually at cruise flight even that knowledge would have been a mere "nice to have".

And for the record, while I am a non-pilot and have never flown solo, I have been at the controls of gliders and trainers in my youth. I'm not just some techie trying to dictate the way you should fly, I'm just saying that there are valid reasons why the design is the way it is.

And had they let go of the controls then the elevator demands would have ceased and the trim would have returned to neutral. In addition, the trim wheel is available to move the THS back to a neutral position far quicker than the autotrim would have. There were plenty of ways to recover, but the overriding problem is that the crew failed to recognise the situation they were in and the reason they were in that situation (overcontrolling at altitude). The reason they overcontrolled was because their training was lacking, which is the fault of the airline and the industry.

Not helpful -the only one showing a dismissive and arrogant attitude is you.

Hi DozyWannabe,

If only that were true.

Once the aircraft was climbing with fixed thrust, and with the stick pitch neutral, the FBW computers would maintain 1 g, and continue to trim the aircraft in pitch as the speed washed off.

In your glider, if you don't move the trim wheel, it will feel heavier in pitch the slower you fly - that feed back is missing with AB FBW.

When Normal Law is working it feels progressively heavy in pitch as speed reduces below alpha Protect, and impossibly heavy if you attempt to fly beyond alpha Max. ALT LAW has no such "protection" (Limits), nor any feel.

Could we get some confirmation from PJ2 or A33Zab?

(@RRR - I don't know about "belief" - I'm asking for some confirmation. Either way it doesn't alter the fact that without overcontrolling, the THS wouldn't have ended up in that position, or that it was possible to set the THS position either by maintaining nose-down inputs or moving the trim wheel. RWA seems to be under the misconception that autotrim commands a THS angle and holds it there regardless of input, when in fact it's just following elevator demand - a mistake I made when I first started looking into this)

Hi DW,

You can't believe it either can you?

It appears that rudderrat is correct.
If only Normal law had been preserved.



ALT law took out the following protections:

• pitch attitude
• low energy
• alpha floor
• high speed
• turbulence damping

Low speed stability protection becomes active. Near stall this brings up a black and red barber pole (oblique stripes?) on the PFD speed. However a black and red ladder (horizontal stripes) is the overspeed!!!
This is surely a trap for mis-interpretation. Why on earth do they use the same colors for overspeed ladder as stall ladder in ALT law! Remember in Normal Law the stall ladder is amber.

Anyone else confirm this?

Bold text as written, and [bracketed] text as I believe was intended.

The French version of this statement on page 78 is more verbose, but has arguably led to a misrepresentation when subject to translation. However the French version is the work of reference, and I've changed the NU inputs to ND inputs in my English copy.

Cockpit Confusion
 

Smiling Ed and Rudderrudderrat – you are patient and well spoken. I like your style.

I am a pilot, though just VFR, and wouldn’t presume to compare my piloting skills with yours or most of the contributors on this site. I do, however, know a thing or two about IT and implementing automated systems. I am not anti-Airbus, anti-Boeing, or anti-anything else. I am pro-arrival-at-my-destination. IT has taught me that thoroughly tested software can – and does – go wrong, and that just because something can be automated doesn’t mean it should be. Critical systems should, IMO, allow human beings to interrupt the automation when appropriate; i.e., “Give me the speed even if it is below your threshold!” or “Give me the AoA even if it is unreliable!” Perhaps that would have helped on AF447.
My hope is that the authorities will consider how decisions made years ago led to some of the confusion in the cockpit. There apparently was a mindset years ago – later reconsidered - that stall was no longer an issue. Did that misplaced confidence in automation pervade the builders and operators? What (if any) other design features are based on the assumption that automation will prevent bad situations? Several people have commented on design and training issues in which pilots lost to IT or bean counters (or perhaps other pilots). These include the stick issues including simulated feel, the lack of AoA indicator, visibility of pilot actions, etc. Dissecting how the old decisions were made, and whether they were good or bad, would be a good lesson in organizational dynamics. I also wonder:

1. What led to the decision to disable SW and displays below certain angles and speed thresholds? Several have said the AoA vanes work fine down to a light breeze. Were 30 deg and 60 knots (IIRC) chosen as limits because out-of-range values are unreliable or because the software would “protect” them from that situation?

2. Why no audible auto-trim? That seems quite an oversight to this novice. A lot of training emphasis was placed on avoiding manual trim. Did the designers think trim – like stall – was a non-issue? Maybe someone felt an audio feedback would just encourage pilots to be more aware of trim, and that was presumably a bad thing. The software, after all, would make that a non-issue.

3. What led to all the laws? The mixed-mode operations and varied levels of degradation seem confusing and counter-intuitive. I read it in the comfort of my chair with tequila at hand. How would it feel to be handed this situation at altitude, mid-Atlantic, 200 souls on board, improperly trained, for the first time?

IMO, too much false confidence in a number of areas led to the disaster. Designers were confident of “protections” that didn’t cover all the bases. AB failed to appreciate the significance of the pitot failures and the risk of simultaneous loss. AF was unable/unwilling/unaware re training issues. The gentlemen flying the aircraft were handed a basket of snakes. I’m not qualified to say anything about their actions, and hope never to be handed a situation like that.
Pardonne-moi pour le poste de longue.

Baro-inertial Vertical Speed
 

Hi Blujet,
Welcome back, sir.
Did you check 34-14-00?
In fact, the Vertical Speed displayed is either "baro-inertial" (not only inertial) or "barometric". My first guess, from graph, was that no inertial V/S data was displayed passed -10,000 ft/mn. But it is not correct. The word range is +/- 32,768 ft for baro-inertial v/s, and only +/-20,000 ft for barometric V/S.

So, in fact, the reason should be simply because all ADRs were rejected by they respective IRs (this 0211 FLR ACARS discussed previously). It will become NCD and replaced by ADR source V/S on PFDs.

- Inertial vertical speed (365) and inertial altitude (361) computation:
The IR software contains a baro-inertial loop to compute the Inertial Vertical Speed and Inertial Altitude. This loop permits to take advantage of the different qualities of the inertial and air data systems. The IR brings its better behaviour in dynamic maneuvers while the ADR brings its stability in time (no drift of the outputs like in IR).

The ADR source to be used is selected according to the configuration of the discretes described previously. When no ADR source is available, Inertial Altitude and Inertial Vertical Speed are sent with their status matrix coded NCD (No Computed Data).

The principle of the baro-inertial loop is given here:
http://takata1940.free.fr/baro_inertial_vs.jpg

Arrogance is to assume that anyone who really flies worries about V_office-chair.

ALT law took out the following protections:
pitch attitude
low energy
alpha floor
high speed
turbulence damping

I'm curious why the pilot pulled up with no overspeed warning. Since the CVR had no such warning why did he pull up? Inexperience or trapped pitot presure with his climb causing static pressure to indicate an overspeed with no warning.

The initial pull up immediately after AP disconnect IMHO was because pitch was 0 deg, altitude descending. For some reason his 2/3 deflection pull up maintained a level altitude for a number of seconds (downdraft?).

Subsequent pull ups IMHO were because he saw the red and black barber stripes (low speed stability protections for stall only showing in ALT/DIR LAW) on his speed and mis-interpreted as the red and back horizontal striped ladder of overspeed. The actual speed showing as being low - but he understood speed had failed. In normal law the low speed bar is amber.

Happy if someone can debunk/support my speculations.

32,768
 

Just a number to many people. It is in takata's post a bit above, #1698. But it has a special significance in computer programming. It is half of a "64K" space, sometimes called a page space. In the simple program "Notepad" it was the maximum number of characters in any note you wished to jot down, for example (at an earlier time). Usually adequate for that, but if not, too bad.

Here it is the number of possible ft/min, up or down, that can be displayed, for vertical speed. I don't want to argue here whether it is an adequate number, but simply to point out the way in which the binary computer efficiency considerations can influence the range of "instrument" displays.

The numbers in this 64K space require 15 binary bits (ie 0 or 1) to represent them, plus a 16th to represent the sign. Computer words are commonly multiples of 8 bits in length these days.

Actually, in one version of implementation of this numbering, 32767 positive values are available, 32767 negative values, and two zero values. That's right, there are two zero values in the most simple arrangement-- plus zero, and minus zero. That wouldn't be so bad if level flight didn't require a zero value. I'm not being facetious here-- this one issue alone required a lot of attention in many computer applications over the years.

The point here is that there are many things in control by computer program that are subtly different from the way we are trained to think, and may occasionally lead to unanticipated results in service. This is going to be particularly true in computers pushed to the maximum in speed with a minimum of size, weight, and power consumption; using software written by people in organizations under similar pressures, to some extent.

The views of pilots as to how such software is working in practice therefore deserve some respect. Unfortunately, once the aircraft is sold, the rewriting of software doesn't contribute anything to the making of that sale.

Illusion, deceleration, and weather.
- Illusion because altitude recorded is "indicated", then partially false at UAS point.
- Deceleration, because autothrust started to reduce N1 by 16% seven seconds before UAS event.
- Weather because there was an up/down/up.

Easy, there is no low/high speed stability in Alternate Law 2b, No red and black striped "barber/ladder".
I already mentioned that many times: SPEED LIMIT FLAG ON PFDs (both).
Neither did the speed "fail" at this point; they "failed" (NCD) when sensed under 30 kt during the stall sequence, much later.

Bea int rep 3 - p76 en - p78 fr
 

You're absolutely correct.

Hi DozyWannabe,
I disagree.
According to the description given in FCOM the aircraft will attempt to maintain pitch and 1g. Even stick free, whilst climbing and decelerating - it will trim more nose up. At the apogee, as it started to fall, provided the sensed g was greater than g/2, then it would trim even more nose up in an attempt to hold 1g.

Perhaps you wouldn't find any of that confusing because it behaved as it was designed, but with a lifetime of conventional aircraft handling qualities behind me - I would most definitely find it confusing.

Normally, when the automatics don't do as we want - we take manual control (as a simple starting base) and then add the automatics gradually.
This crew never had a simple manual control starting base.

I usually only read and don't post here, but...
 

Been a systems engineer for almost 30 years now, and I've never heard of a signed 16-bit implementation different from the traditional -32768 to 32767 that has exactly one representation for zero (what you call "minus zero" actually being -32768). Any reference to this particular implementation you're mentioning?

Old engineer as well.

On a speed base, the IRs decide to reject the ADRs, but still prefer to be replaced by them on a V/S base ... it is getting complex again ...

Now, how to qualify the AF447 event ... ?

Anyway, thanks for your research takata, that's interesting documentation.

3holelover - indeed it was a perfect storm. It was as if the events were tailored to send that specific pilot to the briny deep.

My imagination stretches farther than yours, I guess. I remember me when I got out of college. I surprised many of my new peers with my understanding of electronics. I still needed some pointers. Then I learned why I surprised them. I saw some other raw graduates who'd never fallen in love with their chosen profession and learned, avidly, everything they could. They knew the bare minimum to hold their grades. They were good. But, faced with something outside their specific schooling left them in shock until somebody older poked them the right way. (I think I alienated a lot of fellows when I'd tinker in the corner and finish the project they were working on while I was also tinkering with the project I had at hand. Thankfully nobody ever asked me to build something into neat little boxes. We had some very good lab technicians for that, thank God! I'm not quite helpless when faced with tools and scratch building. (sigh))

He was schooled. He knew what he was doing. But the precise sequence of events threw his schooling right out the window and, it seems, "I want UP" screamed through his system as logic left.

Smilin Ed, out of curiosity what is the rate of change for the THR in manual control mode? How fast can it move 13 degrees? If 0.65 degrees per second is as good as it gets does that adjust your distaste for the auto-trim in any way, especially if that magic number and the actual time it takes to go from neutral to stop in both directions are taught very clearly in training?

If 0.65degrees/second is as fast as it gets and the pilots know this instinctively them holding the elevator is a one control option for controlling the elevator and spinning the trim wheel. You get the same effect.

I've been wondering if there is some place on that panel to put a cartoon of the plane that shows the control surface positions as reported by the feedback position sensors. It could be ignored until a pilot wonders if something is wrong or stuck. (Or perhaps if the PF was mucking it up.)

And, please, I am just asking. Knowing is better than guessing, not that I expect to ever be writing such software. Maybe somebody else who will be designing such software will read it and consider it fully.

alainthailande, as an engineer practicing for even more years than that I have heard of the double zero implementation. Most of the old vacuum tube er empty state electronics computers used it. Sign magnitude is not particularly uncommon until the last 30 years or so. (Gawd - 1980 is THAT long ago! Maybe more like 40 years?)

(Honest, I still have some black hairs..... I'm not all the way white! Suddenly, though, I feel staggeringly old! Um, and when I was a kid the age I am now was considered to be quite old, too.)

Marketing and performance
 

Old Engineer #1701 wrote:
" Once the aircraft is sold rewriting of software doesn't contribute anything to the making of that sale." True enough, if that is the only sale that you as a Salesman hope to make with that Purchaser...
The Marketing Department would wish from more sales from a satisfied and profitable Customer.
I have mentioned earlier that one manufacturer, B., sent me an overnight Telex on how to load their, our, aircraft. Another manufacturer, also called B. whose aircraft we operated, could not, or did not wish to do so... and did not...
Guess which manufacturer was successful in further orders...