CABLE vs FBW

[DC-ATE]

Cable vs Fly-by-wire

Under Rumours & News in the Plane Down in Hudson River - NYC and Airbus crash/training threads there is much talk about the good and bad with FBW. Every time an accident/incident happens with a FBW aircraft, this discussion always comes up. Perhaps a seperate thread dealing with "Cable vs FBW" might be in order.

Myself, I'm a "cable guy". I've always like the idea of being "connected" to whatever it is I'm doing, whether it be flying airplanes, driving a car, truck, or boat. The idea of electric signals being sent to some computer that has to think about what it is I'm trying to accomplish, and then sending that signal to some other computer to actuate some other device, to me seems absurd. Granted this can all be done in a split second supposedly, but it still isn't a mechanical link. I dread the day that FBW gets into the automotive, or maritime industry. If someone will prove to me that FBW is safer than cable, perhaps I'll "come of age".

OK, I've started this thing. Does anyone care to continue it?:)

[NigelOnDraft]

Which is the most recent true "cable" (large) airliner built? 757/767 was not... ;)

NoD

[Centreline747]

I understand your thinking, but this could turn into yet another Boeing/ Airbus slagging match!! :ugh::ugh:

Rgds

CL747

[airfoilmod]

Historically, FBW was developed for military a/c where instability was part of the control regime. A/C were too demanding of human control input, and many a/c could only be flown by computer. Military requirements are light years away from low and slow, there are dozens of missions, not just one. It will remain a discussion for years, I think. AB have proved the mission consistency of the concept, but no format is accident proof. When an argument is sliced as fine as FBW vs. (sic) Cable, it becomes merely preference, and that having developed through time. To a proud pilot, FBW seems arrogant, to another it seems preferable.

The bottom line? How proficient is the Captain and FO on either format?

AF

[18-Wheeler]

I dread the day that FBW gets into the automotive ....

It has been for over a decade.
Drive-by-wire throttle has been in some Toyotas (and no doubt many other cars) since at least 1998 that I know of. I have one of those engines transplanted into one of my cars.
The braking system is also being dabbled with, Mercedes for example have or at least had a system that varied the pressure to the calipers based on how quickly the pedal was pushed; In a panic stop it'd sense you stomping on the pedal and so direct a lot more pressure than normal into the system.
Electric steering is also being looked at and has been tested on company tracks. By electric, I mean there is no mechanical steering rack, etc.

It's here already.

[DC-ATE]

"Which is the most recent true "cable" (large) airliner built? 757/767 was not... "

Ah.....three guesses. The DC-ATE.

[DC-ATE]

18-Wheeler (http://www.pprune.org/members/35140-18-wheeler) -

I was not aware of the things you listed. I won't be buying or riding in any of those.

[Clandestino]

DC-ATE

For young folks: he means Boeing MD-80.

For not so young folks: he means McDonnel Douglas DC-9 Super 80.

FBW or not, I don't care. If the aroplane has proper type certification and is properly maintained, what intersts me are: size of the paycheck, days off and stability of the roster. Both fly-by-cable and fly-by-wire aeroplanes never failed to return me safely to ground. I have no reason to believe that fly-by-hydraulics will be different.

[stepwilk]

Automotive fly-by-wire is inevitable, because the autonomous automobile is inevitable--i.e. a vehicle that does the driving for us. I've written about this, and yes, I've heard all the pry-my-car-out-of-my-cold-dead-hands outrage, but you're wasting your time resisting it.

We live in an age where driving skill is rapidly declining and where distractions are rapidly increasing. Sure, there are Michael Schumachers here and there, but the vast majority of motorists have no idea how wide their vehicle is, which is why you see them driving down the middle of the two-lane road, and are as talented at skid control as they are at playing the twelve-string guitar (which, incidentally, is why a considerable number of new models have FBW stability-control and anti-rollover platforms).

So in a decade or two we will have a nation of drivers (at least in the U. S., unlike Germany, say) who have only enough driving talent to back the car out of the garage and put it into drive, and who have bought their car specifically because it offers Internet connectivity, video, and a variety of voice and other comm systems. They will _require_ an autonomous car.

The interesting thing is that all of the hardware to make this work--yaw sensors and other accelerometers, cruise-control radar, GPS, telematics and all the rest--are already on the shelf. We need some software, but DARPA has already shown that totally autonomous vehicles, without even a driver aboard, are eminently possible.

So if you won't buy or even ride in FBW cars, you're eventually gonna be walking.

Stephan Wilkinson

[DC-ATE]

Centreline747 -
"I understand your thinking, but this could turn into yet another Boeing/ Airbus slagging match!! "

That was NOT my intent as Boeing already has some FBW technology installed in newer models.

Merely trying to determine the merits of one over the other.

So far no one has shown one being 'safer' than the other.

[dixi188]

The Airbus A300 is a proper cable controlled aircraft, assuming cables to power flying control units is considered cable controlled.

If not and we mean non powered control aircraft we probably need to think about DC-7 or Lockheed 1649 Starliner as the last large aircraft with cable controls. (I stand to be corrected)

Even the afore mentioned DC-8 had some powered controls, Ailerons I think.

The Lockheed Electra has boosted controls which when de-boosted are just cable controlled.

I'll duck now while people shoot me down!

[Centreline747]

DC-ATE
Like I said I understand, I was just implying that we keep this a civilised thread, amongst the professionals out there, in what could be a very interesting discussion of the pros and cons of what is, and will become, the future in civil aviation and in the long term will affect all of us. :):)
I look forward to the replies.

Rgds

CL747

[DC-ATE]

Yes, the DC-8 had powered controls. In fact they were all boosted. But in the event of loss of hydraulic power, there were cables for backup if only operating tabs. You could still fly the airplane. It just took a little more muscle!

Other than cost, I'm just wondering why we gave that up.

[Jofm5]

All,

Firstly I am not a pilot so please be gentle with the beatings......

However, from my limited understanding mainly gained by reading threads on here and researching both boeing and airbus use FBW on their later series and indeed earlier models of the former were servo assisted as the strength required to counter the pressures involved is immense.

As an observation I think alot of the preference of direct input comes from the reassurance that computers can and do fail so the direct connection does indeed leave the PIC with direct inputs to control the plane.

I can see advantages in aircraft design in using the FBW approach as cables will require unobstructed pathways down the length of the aircraft and these will require more maintenance as correct tensions and lifecycles need to be observed. I would envisage it be easier to route multiple redundent wire looms than cables.

The major issue I believe with the FBW approach is the involvement of the computer and how much this takes away from the PIC. There are also the issues of computer failure (multiple redundancy should prevent this being an issue). I cannot answer whether the above does indeed take any feeling away from the PIC but you guys would be able to answer that better than me.

Interestingly I think the whole boeing vs airbus argument is more related to sidestick vs yoke than fbw - my personal opinion is the sidestick seems to be less natural but I guess it is more what your used to.

[Storminnorm]

DC-ATE. Could weight and cost have any influence on it?
Blooming great heavy wire cables against fairly light
electricery wires, and who needs to check cable runs
with a TENSIOMETER any more?

[DC-ATE]

Storminnorm -
"Could weight and cost have any influence on it?"

As I have said a few times.....YES! I've always been more concerned with safety than cost. That's why I was critizised a few times for carrying a lot of fuel.

[Storminnorm]

As we used to say. The only time you have too much fuel
is when the flames are licking round your *rse.

[DC-ATE]

Centreline747 -
".....I was just implying that we keep this a civilised thread, amongst the professionals out there, in what could be a very interesting discussion of the pros and cons of what is, and will become, the future in civil aviation and in the long term will affect all of us."

While I am highly biased (and admit it) because of my age perhaps, I hope as well to keep it "civilised". I'm never too old to learn I hope even though I doubt I'll ever be in control of any FBW aircraft.....except perhaps in a sim!

I just want input on the safety issues.

[NigelOnDraft]

I just want input on the safety issuesOK.. a more serious reply than my 1 above ;)

Has FBW yet caused a fataility? The only accidents I can recall that seem the FBW was a "signficant factor" are QF72 (likely) and the Iberia A320 at BIO... neither of which had fatalities?

Has FBW saved any lives? Hard to say... but I guess it could be argued that at Habschiem (sp?) the FBW did save lives :D BA38 might be interesting to see if the FBW made things easier / gentler?

NoD

[DC-ATE]

NigelOnDraft -
"Has FBW yet caused a fataility? The only accidents I can recall that seem the FBW was a "signficant factor" are QF72 (likely) and the Iberia A320 at BIO... neither of which had fatalities?

Has FBW saved any lives? Hard to say... but I guess it could be argued that at Habschiem (sp?) the FBW did save lives BA38 might be interesting to see if the FBW made things easier / gentler?"


Valid points. Guess I should not only include FBW as far as flight controls, but engine inputs as well.

As can be no doubt be determined; I'm against computers controling just about anything where a human is ultimately responsible for the final outcome. Oh, sure, we've come a long way. But everytime I see an "upgrade" with some computer file or program, there seems to always be a de-bugging period before it settles down. It keeps untold thousands of people employed though.

Guess I'm just from the 'old school' of K.I.S.S.

And.....if it ain't broke, don't fix it!

[ChristiaanJ]

DC-ATE,

With the title being "CABLE vs FBW" I have the impression you're barking up the wrong tree.

Most of the issues being discussed in Rumour & News have nothing to do with the way control surface deflection commands are transmitted from the pointy end to the left-and-right flappy bits and the blunt end, and everything with what the various computers do between the pilot's control inputs, either via a joystick, or a yoke, and the commands to the control surfaces.

I'll stay a moment with the "cable vs fly-by-wire", i.e., the transmission mode.

Cable isn't all that great. They rub and chafe (and can break...). They need a lot of rigging and regular adjustment. In a long aircraft, they tend to be affected by the simple fact that an aircraft isn't rigid (DC-8 comes to mind).
Not to mention that, more often than not, they are moved by a relay jack up front, and in turn they move servo valves on hydraulic power controls at the other end.... so there's no direct manual connection anyway.

Fly-by-wire as such, or "electrical signalling" as us oldies called it, is not exactly new, and neither is it rocket science.
The Vulcan used it, and so did Concorde, so we're talking 40 years plus....

Concorde had dual monitored signalling channels AND a mechanical back-up with cables, PLUS a control wheel steering mode (strain gauges) in case something jammed the cockpit controls.
While those modes were regularly trained for, I can't remember anybody describing a reversion to mechanical or to CWS on Concorde in normal service... a few reversions from 'blue' to 'green', yes, but that was about it.

So Concorde already pretty well settled the "cable vs electrical signalling" issue. On the A320 etc. the redundancy issue is settled by four separate "electrical signalling" channels, IIRC. No more mechanical back-up, but still a few tricks up the PIC's sleeve, just in case...


I readily admit to being an ancient, and not properly conversant with the control laws and logic on the A320 or on the B737NG (which usually lead to the A/B wars :) ). But I think the "cable vs FBW" notion as such is a non-issue. I would say that 'FBW' is mostly used as a misnomer for the various computer control modes used in the Airbus family.

Over to you.

CJ

[FE Hoppy]

FBW on the E-jets has two modes. An analogue "direct mode" with no software processing and an augmented "normal mode" where pilots inputs are summed with processed inputs from the flight control modules. Direct mode is nothing more than a multi channel replacement for cables where the pilot has full authority over the control surface. In this mode the only FBW v Cable argument can be weight and serviceability. FBW wins hands down in both.

[Cyclone733]

Given the choice between cables and pullies or electronically signalled flight controls I'd take the latter.

Cables can fall off pullies and be easily jammed by loose objects.

Fly by wire or fly by light can seem to be an over complication, but in the case of civil aircraft the number of backup systems and modes covers the majority of eventualities.

Both control types on modern aircraft tend to have an artificial feel unit for powered control surfaces, so there is no improvement in the pilots feedback from the controls in the case of cables. In the case of more modern cable controlled powered control surfaces the cable only operates the hydraulic servos and offers no manual control of the surface in the event of a total hydraulics failure. Although there is often an electric trim tab

Of more interest to me is the processing of control inputs between the flght deck and the controls. The FBW systems can account for a higher number of variables than an arrangement of pulleys. This will hopefully lead to damage tollerant aircraft which can adapt to damage or failure of flight control systems. It also allows for a greater intigration of the automatics into the aircraft.

[DC-ATE]

ChristiaanJ -
As I stated in another post, perhaps the "computer controlled" engines need to bne grouped in this discussion as well.

As to:
"(DC-8 comes to mind).
Not to mention that, more often than not, they are moved by a relay jack up front, and in turn they move servo valves on hydraulic power controls at the other end.... so there's no direct manual connection anyway."

That's not all true. The tabs are directly connect by cable. Read one of my previous posts.

And as to:
"Cable isn't all that great. They rub and chafe (and can break...). They need a lot of rigging and regular adjustment. In a long aircraft, they tend to be affected by the simple fact that an aircraft isn't rigid..."

Quite true. That's why there's periodic inspections.
And, I'm not interested in which aircraft are FBW/Computer controlled now or in the past. I'm trying to get some input on WHY folks think its SAFER.

And your:
"On the A320 etc. the redundancy issue is settled by four separate "electrical signalling" channels, IIRC. No more mechanical back-up, but still a few tricks up the PIC's sleeve, just in case..."

...points out the fact that they're not quite sure of themselves if they have to have that many back-ups.

On the DC-8.....CABLES were the back-up! Otherwise it was hydraulic power.

Your last:
"I would say that 'FBW' is mostly used as a misnomer for the various computer control modes used in the Airbus family."

I don't think it's a misnomer at all. It describes the system exactly: electric, read wire.

Gee...isn't this fun?!

[Lemurian]

The title, and therefore the whole argument of this thread is too -and by far - simplistic.
It should be about whether or not automation is necessary in our flight decks...and that's going very far back in time.
The main gripe of those arguing about FBW is the "out-of-the-loop" pilot discussion, but it is not a new one : with the big jets era, we've seen a lot of automated systems that were quite acceptable although they took a lot away from the guy in the nose ; to cite a few :

Anti skid brakes
Yaw dampers
Air / Ground sensors allowing a config generated permission for brakes, steering, reversers...etc...
Electronic auto-pilots and CWS modes allowing easier handling (the DC-10 uses it a lot)

.......
As for the engines, may I just remind the younger ones that the original 747 engine was so sensitive to throttle variations that they needed to be restrained in flight ?
All these systems, as I said have been quite welcomed by the pilot profession : A Mach trim acts without any pilot intervention but it was pretty important...so was the yaw damper...and no one questioned the usefulness of an antiskid although one could have one's foot to the pedal stop with not a single psi going to the brake cylinder ...
Were these protections a necessity ?
Well, just have a look at the AC DC-8 in Toronto when the crew thought wise to deploy the [b]ground spoilers/b] on landing....109 fatalities...
A quick research on the various accident data bases will show that cables and pullies were not that safe.
Now came the 320 and its followers along and aviation became another proposal altogether and the opponents became a lot more vocal (That thing is going to take away our skills...we're now truly out of the loop...)
Yeah ! Sure !
But people have a rather short memories : the so-called "hard limits" they were so against would have saved quite a few lives ; just two instances :

EAL DC-8 on a degraded stability in turbulence just after take-off...58 fatalities (25/2/64)
JAL DC-8 in Moscow, with a "supercritical AoA" ... 61 fatalities (28/11/72)

One of the arguments for FBW is weight and cost. Can't disagree, really. But we've come to a point were the control of most our equipment is so fine, with so few tolerances that a mechanical solution is totally out . I still remember studying the fuel system of a DC-4 engine : valves here, valves there, a baro tube pushing a membrane which in turn pushes a rod that actuates the opening of yet another valve...and what did the "poppet valve do ?". They were brilliant pieces of engineering (just have a look of how the constant speed of a propeller was achieved !), but may I just remind you that not one of these marvels could qualify for the shortest ETOPS performance (If I remember well, the most beautiful of these machines, the Connie was also called "the best Trimotor over the Atlantic").
FBW C* laws are here to stay and I for one welcome them. Mind you, there could still be some gremlins hanging about in those softwares : One which is well known, and therefore designed into every system is about discrepancies between pilot inputs and response speeds from the controls....studied at length at Airbus Industries but they couldn't envisage the coupling that they got on the Bilbao incident (problem now solved).
On the other hand, I can't help but feel a bit sad that an accident that would have been avoided on a FBW equipped airliner happened on an MD-80 on August 16, 2005 with the loss of all aboard.

Just my two euro cents.

[Centreline747]

Just to add a little log to the fire, the 747 classic (and I suspect the -400) is all cable and pulleys from the control column to the hydraulic actuators, but if you lose all hydraulics, which is highly unlikely with 4 systems, you do not have any 'manual' back-up. You cannot move the controls by conventional cable link.
Does that mean it is fly by (cable) wire??? ;)

Rgds

CL747

[repariit]

It seems to me that Cables vs FBW misses something. There needs to be a third category. Some of the discussion here is treating "cables" as aircraft capable of a manual reversion where you can fly by actual cables attached to tabs that will move surfaces aerodynamically. And, on the other end meaning the Airbus FBW system.

In the Boeing line the 727's and 737's fit the "cable" definition, but the 747 does not. If all of the redundant hydraulic systems are drained, there is nothing tying pilot to surfaces, yet it is not FBW either.

There may be similar trust in cables and hydraulics, and less trust in computers and electrons by some in this discussion.

[DC-ATE]

Lemurian =
"Well, just have a look at the AC DC-8 in Toronto when the crew thought wise to deploy the [b]ground spoilers/b] on landing....109 fatalities...
A quick research on the various accident data bases will show that cables and pullies were not that safe.
Now came the 320 and its followers along and aviation became another proposal altogether and the opponents became a lot more vocal (That thing is going to take away our skills...we're now truly out of the loop...)
Yeah ! Sure !
But people have a rather short memories : the so-called "hard limits" they were so against would have saved quite a few lives ; just two instances :
EAL DC-8 on a degraded stability in turbulence just after take-off...58 fatalities (25/2/64)
JAL DC-8 in Moscow, with a "supercritical AoA" ... 61 fatalities (28/11/72) "
-----
Toronto: nothing to do with the fact that it was cable operated.
Lake Pontchartrain: same thing.
Moscow: Don't have a report.
-----
".....DC-4 engine : valves here, valves there, a baro tube pushing a membrane which in turn pushes a rod that actuates the opening of yet another valve...and what did the "poppet valve do ?". They were brilliant pieces of engineering (just have a look of how the constant speed of a propeller was achieved !), but may I just remind you that not one of these marvels could qualify for the shortest ETOPS performance (If I remember well, the most beautiful of these machines, the Connie was also called "the best Trimotor over the Atlantic")."
-----
Ah.....brings tears to me eyes! Speeder spring and poppet valve. How 'bout the A, B, C, and D chambers?

The fact that the Connie MIGHT have been referred to as you say had nothing to do with the fact that it was cable operated.
-----
"On the other hand, I can't help but feel a bit sad that an accident that would have been avoided on a FBW equipped airliner happened on an MD-80 on August 16, 2005 with the loss of all aboard."
-----
If you're referring to West Caribbean Airways MD-82, I don't see where being cable operated had anything to do with that. They lost both engines. And, I'm not familiar with the MD-82 and whether it is controlled the same as the DC-8.

[DC-ATE]

Centreline747 -
"Just to add a little log to the fire, the 747 classic (and I suspect the -400) is all cable and pulleys from the control column to the hydraulic actuators, but if you lose all hydraulics, which is highly unlikely with 4 systems, you do not have any 'manual' back-up. You cannot move the controls by conventional cable link.
Does that mean it is fly by (cable) wire??? "

That being the case (I'm not qualified on the 747), it's not cable operated in the same manner as the DC-8 is, is it?

[Lemurian]

DC-ATE
Toronto: nothing to do with the fact that it was cable operated.
Lake Pontchartrain: same thing.
Moscow: Don't have a report.
Are you a bit dishonest ? because if that's the case, there is no point at all in this discussion.
You advocate purely mechanical links between the pilot and the flight controls (plus or minus a hydraulic servo) and claim it was safer ("if it ain't broke, don't change it").
The three instances happened with unprotected flight controls, i.e. not FBW.
As for the MD-80, the flight controls of which are basicaly trim tabs, the crew couldn't manage a clean best glide angle, and speed, which could have helped a lot their relight attempts, and I'm not even talking about the characteristics of that airflow over the wing and it's influence on the engines'intakes....and they went down to crash on a series of consecutive stalls... It wouldn't have happened on an FBW airplane.
On th same subject, just imagine another unprotected airliner during the descent and ditching of USAir 1549...just 5 knots over stall speed but still under absolute control on all axises... If anything, that instance would make me a believer of the advantages of an FBW airplane.

[ChristiaanJ]

....and they went down to crash on a series of consecutive stalls... It wouldn't have happened on an FBW airplane.Again.... !
Fundamental confusion between FBW - fly-by-wire - as a concept, and what has been added since.

FBW as such has nothing to do with stall protection, etc.

In the olden days, we had fly-by-wire (see my earlier post), which just replaced less reliable and heavier wires.

In those days we had stick shakers, stick pushers and suchlike, as stall protection. Which you could ignore at your own discretion.... if you knew what you were doing.

Then came Alpha-Floor and all that, and if you didn't understand that, and didn't understand either that an engine needed time to spool up, and that you didn't do an "air show" below limits with a full load of passengers at an airfield you'd never been to before, yes.... you'd end up with something like Habsheim.

CJ

[DC-ATE]

Lemurian -

The Toronto accident was pilot error. The F/O actuated the spoilers 60' above ground on a DC-8.....strickly a NO, NO!

Lake Pontchartrain was an apparent failure of the PTC.

And, as I said, I don't have the info on the Moscow accident.

I won't discuss the MD82, because I know nothing about the DC-9 series A/C.

And as to:
"Are you a bit dishonest ? "

Would you care to elaborate on that remark?

[Lemurian]

DC-ATE :
The Toronto accident was pilot error. The F/O actuated the spoilers 60' above ground on a DC-8.....strickly a NO, NO!
On a 'Bus ( for instance), the ground spoilers would not deploy in an in-flight configuration, and in an alpha prot situation, the spoilers would have been retracted.
And btw, the co-pilot was only arming the ground spoilers, not extending them.
Lake Pontchartrain was an apparent failure of the PTC.
Wrong : the PTC had been MELed and was inoperative on that flight. The elevator position was from crew action (manual wheel).

The JAL DC-8 crashed in Moscow because of -another- spoiler extension just after takeoff, causing the AoA to increase beyond stall.

As to my remark, or my question, rather, it still stands : Are these accidents related to flight controls or not ?

Christiaanj
Fundamental confusion between FBW - fly-by-wire - as a concept, and what has been added since.

FBW as such has nothing to do with stall protection, etc.

Sorry, Christiaanj, you can't dissociate the concept of FBW and the safety aspects it brought to our industry because they are at the heart of this discussion, some claiming their distrust of the concept, others with a different agenda. As a matter of fact, the protection concept appeared right at the beginning of the A300 test bed electrical signalling study : they were the natural inherent progression of the initial design. That Boeing chose a different path for its projects belongs to another discussion.
I have been flying the 'Bus for thirteen years now, after some experience on classic hydraulic-boosted flight controls - and some cable-and-pulleys- types and I've found the electrically signalled flight controls to be far superior, in terms of comfort, ease of flying, accuracy and safety.
This term of safety needs to be elaborated on a bit further : People only think of safety through the envelope protection of the different FBW realisations...OK, but the qualities I've eluded at also participate : flying with an always in-trim aircraft, with exactly the same perceived respone whatever the configuration or the speed takes a lot out of one's mind, making one quite a bit more available for the main task of flight management.
Please note that on my previous post I was already disputing the title of the thread, which should be more about flight deck automation -and its ultimate realisation : the FBW, envelope-protected airliner- rather than just replacing mechanical links with a bundle of electrical wires.
In those days we had stick shakers, stick pushers and suchlike, as stall protection. Which you could ignore at your own discretion.... if you knew what you were doing.

The problem goes far beyond that as there are moments when the task at hand exceeds one's capabilities : think of all the instances of windshear-caused accidents. Are they pilot errors ? Now compare the last instants of these cockpits with a "WINDSHEAR TOGA" maneuver in a 'Bus...didn't we make some real progress here by providing the guy in charge with an easier/safer tool which gives him the full maneuvering capability of the FBW system ?
All that said, I'm not naive enough to think for one second that FBW is the ultimate panacea and that it did not introduce a few traps in flying...Most of them are human factors-related : what confidence in the system, what about trust, what about complacency, and human-machine integration ?
I for one don't take anything for granted. I'm certainly not the only one around.
Onthat aspect, this study deserves some careful reading as it goes a lot beyond the "if it's not a DC-3, I won't take it"- type of argument :
Perceived Human Factor Problems In Flight-Deck Automation (http://www.flightdeckautomation.com/phase1/phase1report.aspx)

[Dan Winterland]

I found the title of the thread quite unambiguous. it was really just questioning how the flying controls received their signals and was it relevant to the Hudson river incident.

Well, it was relevant in that the crew would have had the flying controls degraded two steps from Normal Law, through Alternate Law to Direct Law. This means that the controls move proportionally in realtion to the stick movement. Just like they would in a cable controlled aircraft such as an older Boeing design. The crew would have also lost a lot of the protections such as V alpha Max which would initiate an auto go around - if they still had engines!

So there is a difference, but it's no big deal and not of huge relevance. It just downgraded itself down to a 737!

[DC-ATE]

Lemurian -
"And btw, the co-pilot was only arming the ground spoilers, not extending them."

Ah...you yourself stated in #25:
"the crew thought wise to deploy the [b]ground spoilers/b] on landing...."

The F/O did not "arm" them; he EXTENDED them.
Are you being a bit dishonest?

Without reading the reports on the other two, I won't comment. I do recall something about the PTC being deferred. But so what? Stuff happens.

[Lemurian]

DC-ATE
I do recall something about the PTC being deferred. But so what? Stuff happens.
So, stuff happens on a cable-and-pullies airplane and you find it acceptable and you refuse to consider any of the progress made through FBW...
To say the least, strange attitude !

OK, I'm out of here.
Technical discussions are alright, but this is turning to a dialogue of the deafs...my fault, I suppose.

Bye.

[DC-ATE]

Lemurian -

Two of the accidents you listed were the (apparent) result of PILOT ERROR. The fact that the spoilers are 'mechanical' really did not matter.

05 July 1970
Air Canada
Toronto, Ontario, Canada
60 feet above the ground during landing, the speedbrakes were inadvertantly deployed by the First Officer, which resulted in an excessive sink rate. The no.4 engine struck the runway, and a go-around was initiated. The aircraft proceeded to climb out normally, but while on a downwind for a second landing attempt, the aircraft exploded. Ruptured fuel line during the first hard landing.

28 November 1972
Japan Airlines
Moscow, Russia
The aircraft crashed on takeoff after the accidental deployment of the spoilers by the Flight Engineer.

"OK, I'm out of here.
Technical discussions are alright, but this is turning to a dialogue of the deafs...my fault, I suppose."

OK.....have a good day.

[FlightDetent]

the accidents you listed were the (apparent) result of PILOT ERROR. The fact that the spoilers are 'mechanical' really did not matter. I like (so far) the tone of the thread. My opinion is that it DID matter. Rods/pulleys have no check valves or sort. FBW may, as per individual design. Pilot error forcing A/C to go out of certified envelope is mitigable on FBW w/ protections.
Could Cali CFIT had been avoided through last-stop measure of some SW logic auto-retracting speedbrakes when TO/GA thrust is set?

FD (the un-real)

[ChristiaanJ]

Lemurian,
Thanks for the link.

CJ

[DC-ATE]

ChristiaanJ -

"Lemurian,
Thanks for the link."

I read through that and it looks like there's more cases against automation than for it.

[DC-ATE]

FlightDetent -

"I like (so far) the tone of the thread. My opinion is that it DID matter. Rods/pulleys have no check valves or sort. FBW may, as per individual design. Pilot error forcing A/C to go out of certified envelope is mitigable on FBW w/ protections.
Could Cali CFIT had been avoided through last-stop measure of some SW logic auto-retracting speedbrakes when TO/GA thrust is set?"


Indirectly, you are correct. But I suspect a pilot could make a mistake on a FBW aircraft as well with the same results. I don't have the Cali report.

[Dani]

Lemurian, of course automation is a biggy, and I agree with you about whatever you say. But the topic is not about automation, and you are wrong in the - not mentioned - assumption that all electrically wired aircraft are heavily automated.

As others said, the Embraer E-Jets are not "fly-by-wired" like the Airbusses. Also the Saab 2000 is not. Also the 777 is not. Also most aircraft with Fadec and power-by-wire are not. In fact, the only aircraft that is - in your sense - heavily automated is the Bus itself. And it is a good thing. I like it.

But the topic starter was arguing about missing mechanical links between the controls and the actuators. But also this has been identified as not accurate, not safer and not better anymore.

So I guess all has been said and done?

Dani

[Lemurian]

Dani
One could define automation as the existence of a computer between the pilot's command and the control, be it flight controls or engine or navigation...etc...
That definition -which is by no means complete - therefore includes everything that has been included in an aircraft cockpit or systems and takes the pilots away from a "direct" link to the desired information or command.
As for the FBW, whether one could define different levels of protection or not, and through what means, the fact is that a demand by the crew goes through a set of computing steps before the result goes to the concerned system. (forget the loops, for simplicity's sake)
The old A-vs-B argument only lies on definitions of "soft" vs "hard" protection, but it becomes more and more a dispute on semantics ( See the tail strike protection of the T7 for instance ).
Another dispute is about moving/not moving T/Ls. To that one I'd just comment that the BA T7 which managed a glide into Heathrow had both throttles firewalled, which somehow proves that were not indicative of the engines'output...
I'm not familiar with the architecture of the Embraer products but the Airbus philosophy has been adopted by Dassault and now by Bombardier on their C series...and studied closely by the Russians. (Could mean something...).
All the above tell me that the level of automation reached by the modern airliners seems quite wide-spread and a simple quick look at the incident/accident statistics will show that the level of safety the air transport industry has achieved through automation is on another planet altogether compared with the pre-jet era.
Another quick look at the accident statistics of jet airliners also show that the last of the classically flight-controlled airplanes, the DC-9/MD8xxx has a safety record that can't compare with the more modern ones in the same period...(Might say something, too...)
To illustrate my point and although I don't agree with all the arguments presented, this is a paper from the USAF about cockpit automation and its "costs"
Identifying And Mitigating The Risks Of Cockpit Automation (http://www.au.af.mil/au/aul/aupress/Wright_Flyers/Text/wf14.pdf)

[Dani]

Completly agree, Lemurian, I'm the wrong guy to be beaten up.

I just want to tell you that there isn't an imperative incorporation of FBW and automation. To the contrary, "soft-fly-by-wired" aircraft are following a more traditional approach of control technology: Although there is no mechanical linkage, the design is still very similar to "old" cockpit technology: a yaw damper or a stick shaker or a speed limiter is a stand-alone box somewhere alongside the signal stream, and does only interfere when its time has come. It's still not system integration like in modern military solution or like in the Airbus product.

I also agree that only Airbus' way is the way to go - and the longer Boeing is waiting to do something really innovative (I'm no insider of the 787), the more they lag behind.

I'm merely putting down what the topic starter asked or feared. If we can lift the anxiety of some more traditional Aviators we finally get where we want to go: More safety, at lower costs and more environmentally friendly.

Dani

[yowdude]

i've flown the dc9 and now i fly the bus. building time on the 9 was the best experience i got on how to fly the wing. it seems that i can only reminisce on my flights while flying the bus coz there nothing much to do after you set it up:)

[johnnyDB]

there are several recent airliners around with cable operated tabs which directly move controlsurfaces, no computer, no hydraulics.
I'm on about 100-150 passenger jets.

[FlightDetent]

But I suspect a pilot could make a mistake on a FBW aircraft as well with the same results. I don't have the Cali report. Same mistake - yes, but with different, non-tragic results achieved through possibilities provided by FBW design.

My recollection on Cali is that after what is today a textbook CFIT scenario they hit treetops just by a few feet on a ridge during the escape manoeuvre, lost flaps during this intial impact but remained airborne. Only then succumbed down to ground on the other side of a valley. The speedbrakes were left extended throughout the manoeuvre.

On FBW a simple algorithm can be provided: IF ([any]THR LVR >= MCT/CON): SPDBRK := 0. I am not saying a mechanical system with similar effect is impossible to engineer.

Also on FBW with protections (yet another category), you can have the pilot pull full back on pitch control and go to ALPHA(max) which can be set quite close to ALPHA(crit). Without protections, fbw or not (!), a StickShakeLimit becomes the pilots' ALPHA(max) and needs to be set further away from A(crit) to maintain margin for human performance.

Entry to the climb phase is significantly faster with protections and the performance available from the wing is utilized more effectively.

I suspect that comparison of contemporary FWB functions against the Little Rock scenario could also provide some credit to the argument.

Yours,
FD (the un-real)

[DC-ATE]

OK...thanks for that info.

re. "stick-shaker"; what is the stall warning indication on the A-320-type aircraft?

2nd question: Do the A-320 types have tail de-ice?

[NigelOnDraft]

what is the stall warning indication on the A-320-type aircraft?
In "Normal Law" there isn't one, because the FBW makes it hard to get near the stall, and "impossible" to stall...

In other laws i.e. when degraded, it shouts "Stall Stall" at you :ooh:

Do the A-320 types have tail de-ice? No...

HTH
NoD

[FE Hoppy]

Just to add the E-jet.

In both Normal and Direct mode we have a stick shaker at 1.05Vs-1g.
In normal mode when it's firing you can pull back to the stop but the fly by wire will limit the aircraft to Cl max. This is called AOA limiting so like the bus you cannot stall the wing. However, there is no automatic thrust increase at this point so unless you help out you can "stall" the aeroplane. i.e not enough V^2 for lift to equal weight.

In direct mode its just like a cable system and you can screw up as much as you like.


also no anti ice on the empennage.

[Lemurian]

FlightDetent
on FBW with protections (yet another category), you can have the pilot pull full back on pitch control and go to ALPHA(max) which can be set quite close to ALPHA(crit). Without protections, fbw or not (!), a StickShakeLimit becomes the pilots' ALPHA(max) and needs to be set further away from A(crit) to maintain margin for human performance.

Entry to the climb phase is significantly faster with protections and the performance available from the wing is utilized more effectively.

I suspect that comparison of contemporary FWB functions against the Little Rock scenario could also provide some credit to the argument.

Article by ALPA with NASA's help . Excerpts :
GPWS pull-up warnings require immediate crew action. Because most transport airplanes in CFIT accidents have hit within 200 feet of the top of the terrain, maximizing airplane performance at the beginning of the pull-up is crucial. The American Airlines B-757 that crashed on a ridge near Cali, Colombia, hit 100 feet below the ridge line--100 feet was the performance difference between survival and disaster.

A CFIT escape maneuver, a procedure usually performed in response to a GPWS warning, is designed to expediently remove an airplane from an impending collision with terrain. This maneuver is designed around the use of maximum or near-maximum aerodynamic performance. Typically, the airplane is in a descent. A CFIT escape maneuver can be started anywhere from a clean cruise descent (250 to 300 KIAS) to flying with full flaps and gear down at approach speed.

We looked at three cases: airplanes with conventional flight controls, FBW airplanes with "hard" protection features, and FBW airplanes with "soft" protection features.

Conventional flight controls

For an aircraft with conventional flight controls, the typical CFIT escape maneuver requires the pilot to apply maximum thrust and rotate at a smooth rate of 3 degrees per second to a pitch attitude of 15 to 20 degrees nose-up. This pitch attitude is maintained until the stickshaker activates or terrain clearance is ensured. The 3-degree-per-second rate was selected as a target pitch rate to avoid overstressing the airframe in the high-energy case and to avoid stalling in low-energy escape maneuvers.

An industry task force recommended this procedure, and it is the basis for most current CFIT escape maneuver procedures. Also, some operators had airplanes whose stickshaker may be activated by sensing AOA acceleration, and they believed a low-pitch rate was necessary to avoid activating the stickshaker. An operator selects for itself its CFIT escape maneuver procedure, and currently that may not be what the manufacturer recommends. Airlines often want to have a fleet-common procedure, regardless of aircraft type, for cross-training and standardization.

FBW flight controls

For the purpose of this investigation, we chose two airplanes that represent different FBW flight control design philosophies: the B-777 and the A330. We conducted test flights of the B-777 from Boeing Field in Seattle, Wash., and test flights of the A330 at the Airbus facilities in Toulouse, France. A company test pilot occupied the right seat in each case, and evaluation pilots took turns flying from the left seat. We operated both airplanes at a mid-CG with a takeoff weight that would permit the approach-configuration CFIT-avoidance maneuvers to be performed near the airplane's maximum (worst case) landing weight.

In preparing for the flight evaluations, we used the manufacturer's engineering flight simulator to work up a test card and to validate the profile. Simulator data allowed us to evaluate various maneuvers, determine the maneuvers with the best potential for optimal recovery, and practice the selected maneuvers.

Hard limits

Airbus, in the design of its FBW flight control system, incorporates "hard" limits, which prevent the pilot from exceeding a predetermined flight envelope. The FBW flight control system used in the Airbus design maintains an AOA margin to prevent the pilot from stalling the airplane. The aircraft cannot be commanded to exceed +2.5 gs or –1 g clean (regardless of gross weight). The pitch attitude is limited to the range between 30 degrees nose-up and 15 degrees nose-low. The bank angle is limited to 67 degrees. No approved or readily discernable method allows the pilot to override the flight envelope protections.

The A330-200's maximum takeoff weight is 507,100 pounds. For our flight, we weighed 402,600 pounds, just above the maximum landing weight of 396,800 pounds. Our fuel load was 134,000 pounds, with a maximum fuel capacity of 250,000 pounds. The A330-200's two P&W4168 engines are rated at 68,000 pounds of thrust each.

The procedure for Airbus's recommended CFIT escape maneuver in the A330 is for the pilot to pull full back on the stick, apply maximum thrust, and recover when terrain clearance is ensured. The speed brakes, if extended, will retract automatically. Control laws either stabilize the AOA at an optimum value or adjust pitch rate to obtain maximum allowed g.

Soft limits

Boeing, in the design of its FBW flight control system, incorporates "soft" limits, which warn the pilot when a limit is being approached, using such methods as increased stick forces and aural and visual warnings.

With soft limits, after the warning, the pilot is allowed to override and achieve maximum aerodynamic capability of the airplane; you could stall, overbank, overstress, or overspeed the airplane, if necessary or desired. The keyword for FBW soft limits is "overrideable."

The maximum takeoff weight of the B-777–300 is 660,000 pounds, and the maximum landing weight is 524,000 pounds. For our flight, the airplane weighed 501,000 pounds, of which 163,500 pounds was fuel. Two Rolls-Royce Trent 892 engines, each rated at 90,000 pounds of thrust, powered the airplane.

In a CFIT escape maneuver for the B-777, Boeing recommends that the pilot immediately select maximum thrust, rotate aggressively to 20 degrees of pitch, and retract the speed brakes (they do not automatically retract as do Airbus speed brakes), and recover when terrain clearance is ensured.

Flying the escape maneuvers

We flew simulated CFIT escape maneuvers near the maximum landing weight and at an approach speed of Vref +5 knots, with the gear down and flaps at maximum landing setting, at a descent rate of 1,500 fpm. We also flew simulated CFIT escape maneuvers at typical enroute descent speeds (250 and 300 KIAS as permissible), in the clean configuration, at a descent rate of 1,500 fpm. Splitting the task force's recommended 15–20-degree range for target pitch, we flew the maneuvers with a smooth pitch rate (target 3 degrees per second) to a pitch attitude of 17.5 degrees.

We then repeated these maneuvers with an aggressive pull-up (soft protections) or with full back stick (FBS) application (hard protections).

The benefit of the FBS maneuver for the A330-200 was quite apparent. Using full back stick resulted in an altitude loss of 40 feet, as opposed to 68 feet for the 3-degree-per-second recovery (see Chart 1). The evaluation team felt that time below entry altitude was as important a recovery parameter as total altitude lost. The time below the entry altitude was 3.4 seconds for the FBS versus 5.7 seconds for the aggressive pull-up. And finally, the FBS airplane was 172 feet above the 3-degree-per-second airplane, which was just getting back up to the entry altitude. Remember, most aircraft hit the ground within 200 feet from the top of terrain.

In the approach configuration, altitude loss during the FBS recovery was 35 feet, as opposed to 75 feet. The time below the entry altitude was 5.3 seconds versus 7.8 seconds (see Chart 2). And finally, the FBS airplane was 115 feet above the 3-degree-per-second airplane as the latter was just getting back up to the entry altitude.

As expected, data for the B-777 CFIT escape from an enroute descent showed that a rapid rotation method resulted in less altitude loss than did a slow rotation. Typical data showed about a one-third greater altitude loss with the 3-degree-per-second rotation. The test point showed 80 feet lost for 3 degrees per second (see Chart 4) versus 60 feet for the aggressive pull-up. The time below the entry altitude was also less, 3.1 seconds versus 4.7 seconds. The airplane with the rapid rotation rate was 180 feet above the slow-rotation-rate airplane as the latter passed through the entry altitude. Remember that in the Cali accident, 100 feet was the difference between clearing and not clearing the ridge.

The data for the B-777 configured for a power-on approach were interesting. The flight data showed a greater altitude loss for a rapid-rotation versus the slow-rotation maneuver--67 feet versus 50 feet shown (see Chart 3). Our simulator data predicted the opposite. While the data possibly have some scatter, the difference was attributed to the effects of the slow engine acceleration, which we first encountered while evaluating the airplane's stall characteristics.

The Trent engines demonstrated noticeably slow acceleration from low power settings, followed by a perceptible increase in engine noise and thrust surge as the engines "kicked in." After practicing, I could finesse the AOA rate of change during stall recovery to maintain optimum AOA during engine wind-up (I should mention, the test airplane had no dedicated AOA indicator).

In the low-speed CFIT escape maneuvers, however, the B-777's control laws apparently allowed overshoot of optimum AOA during this engine acceleration period, causing a "mush" effect that resulted in energy bleed and greater altitude loss. The 3-degree-per-second pitch-up was slow enough to allow thrust to catch up before the AOA increased to the same relative value.

We felt the Airbus pitch control laws prevented a similar AOA overshoot, even though the Pratt & Whitney engine acceleration times were similar. We did not see this effect in the high-speed escape maneuvers because enough energy remained so that AOA stayed low in both cases.

On the plus side, the B-777 rapid-rotation escape maneuver resulted in less exposure time below entry altitude than did the slow-rotation procedure (4.8 seconds versus 5.7 seconds), even though the altitude loss was greater. Passing through entry altitude, the rapid-rotation airplane was 50 feet above the airplane flown with the 3-degree-per-second rotation rate. On the line, different escape maneuver procedures might appear to be warranted for the high- and low-energy cases, with possibly a low-energy procedure addressing the Trent's slow spool-ups. As mentioned earlier, however, airlines tend to prefer "one size fits all" procedures. In addition, having an AOA indicator in the cockpit might help.

As in any flight evaluation, pilot comments are as important as the hard data. One of our most significant findings is that although we could achieve more consistent and repeatable performance with the "hard limit" design, this evaluation team philosophically preferred the flight envelope limiting features ("soft limits") of the B-777 design to the "hard limit" A330-200 design. This was a subjective judgment based on other handling quality evaluations that we performed and the premise that some situations might arise that the designers had not foreseen and for which the pilot might need to achieve full aerodynamic capability as opposed to being limited by software/control laws.

From our flight test work, we arrived at a number of conclusions and recommendations. First, the A330 full back stick CFIT escape maneuver gave better and more consistent performance than a 3-degree-per-second pull, without any increase in risk of exceeding flight envelope parameters. No additional or specific pilot training was necessary to perform the full back stick recovery technique because the FBW design provides excellent pitch rate and g control as well as excellent envelope protection for stall, overstress, or overspeed.

As a result, we recommend that Airbus FBW operators use the manufacturer's recommended full back stick CFIT recovery procedure. As I previously said, this may seem obvious; but until this report, none of the U.S. operators were following the Airbus-recommended procedure, and none felt that doing so was prudent. In addition, the ease of training and maneuver repeatability, in our opinion, outweigh the advantages of fleet-standardizing an airline's CFIT escape maneuvers for all airplane types.

In the case of the B-777, flight test results indicated that an aggressive pull-up as Boeing recommends yielded better CFIT avoidance performance than the 3-degree-per-second recovery procedure in all categories except total altitude lost in the case of the low-speed, low-power-setting situation. As a result, we recommend that B-777 operators follow the manufacturer's recommended CFIT escape maneuver procedure but consider modifying the procedure in the case of the low-speed, low-power-setting scenario.

As a final recommendation, based upon all of our previous conclusions, recommendations, and pilot comments, we feel that future FBW designs should consider protected flight-envelope limits with envelope-protection override.

I have flown all of the Airbus FBW airplanes and have been able to aggressively maneuver each airplane without worrying about overstressing the airframe. To pull the stick full back in an airplane that weighs half a million pounds and pull right to 2.5 gs is impressive (especially to the chief pilot if the airplane is loaded with passengers!). However, to be presented with a windscreen full of rocks and only a 2.5 g capability when more g is aerodynamically available is not comforting. This is when the capability to pull to the aerodynamic or structural limits of the airplane--as can be done in the B-777--is important. The B-777, however, does not have the carefree maneuvering capability of Airbus FBW airplanes. A combination of the best points from both these designs would be desirable.
Whole article "CFIT AVOIDANCE AND FBW", Here (http://cf.alpa.org/internet/alp/1999/septcfit.htm)


NB : Article written in 1999...Ten years ago !

[DC-ATE]

Quote:
what is the stall warning indication on the A-320-type aircraft?
In "Normal Law" there isn't one, because the FBW makes it hard to get near the stall, and "impossible" to stall...

In other laws i.e. when degraded, it shouts "Stall Stall" at you http://static.pprune.org/images/smilies/icon25.gif


Quote:
Do the A-320 types have tail de-ice?
No...



Therefore, w/o tail anti-ice, the tail could stall before the wing and you would have no warning. I assume that in "other laws" the warning is based on some computer info from some source. But...same problem; tail stalling first.

[NigelOnDraft]

DC-ATE Therefore, w/o tail anti-ice, the tail could stall before the wing and you would have no warningSorry - please expand :suspect:

A320 etc. do not have tail anti-ice because they have been designed not to need it / have been certified as not requring it i.e. either the tail does not ice up (significantly) [in fact I know it does / can], or the design is such that it does not significantly affect the overall flying characteristics when iced.

Anyway, a tailplane typically produces a downforce, is at a lower alpha than the mainplane, has a different - in fact inverse - section, so if it did "stall" surely it would reduce the downforce, letting the nose drop...?

FEH However, there is no automatic thrust increase at this point so unless you help out you can "stall" the aeroplaneSorry - I do not understand why you need thrust to prevent a stall? If this is so:In normal mode when it's firing you can pull back to the stop but the fly by wire will limit the aircraft to Cl max. then so long as the FBW limits you to CL Max, you will not stall, power or no power? Might lower the nose a lot / lose a lot of height, but surely no stall?

NoD

[Lemurian]

NoD
A320 etc. do not have tail anti-ice because they have been designed not to need it / have been certified as not requring it i.e. either the tail does not ice up (significantly) [in fact I know it does / can], or the design is such that it does not significantly affect the overall flying characteristics when iced.

None of the "moving tailplane" equipped airliners needs it to be de-iced, as the authority of that big surface - covered or not with ice - on the control of the airplane is immense ( as witnessed by the "manual back-up" on the 320 : pitch control via the trim wheel necessitates absolutely minuscule corrections ).
See FAR 25 / 1419 and appendix C

FEHoppy
not enough V^2 for lift to equal weight.
That will cause only a descent. It certainly doesn't mean "stall" as you would be always below alpha max.

[DC-ATE]

NigelOnDraft & Lemurian -

Are you telling me that the A-320 cannot get ice on the tail plane? You can't be serious. Boeing said the same thing about the 737 and were wrong. If the wing can ice up, the tail can certainly ice up.

[FE Hoppy]

CS25

Vsr may not be less than the 1g stall speed.

Therefor if I'm at a speed lower than that required to maintain 1g flight I am by definition stalling.

There is also a reference somewhere that refers to the fact that if the control is on the rear stop the aircraft is stalled. I will print it when I find it.

I used the term Wing stalled to reference alpha above that which first achieves Clmax and Aircraft stalled when at Clmax weight is greater than Lift.

I understand the Airbus has Alpha floor which increases thrust to ensure that when Clmax is achieved V^2 is always high enough to arrest descent.

Sorry for the confusion.

Nigel. After flow analysis was complete your Airbus was flight tested with false leading edges on the empennage to simulate the maximum ice build up. the handling characteristics met all requirements so no anti ice system is required.

From CS 25.201 Stall Demonstration.
......
The aeroplane is considered stalled when
the behaviour of the aeroplane gives the pilot a clear
and distinctive indication of an acceptable nature that
the aeroplane is stalled. (See AMC 25.201 (d).)
Acceptable indications of a stall, occurring either
individually or in combination, are –
(1) A nose-down pitch that cannot be
readily arrested;
(2) Buffeting, of a magnitude and severity
that is a strong and effective deterrent to further
speed reduction; or
(3) The pitch control reaches the aft stop
and no further increase in pitch attitude occurs
when the control is held full aft for a short time
before recovery is initiated. (See AMC
25.201(d)(3).)
.....

So when AOA limiting is in effect the control is at the aft stop but the aircraft will no longer pitch up. This indicates the aircraft is stalled.

[Lemurian]

FE Hoppy
So when AOA limiting is in effect the control is at the aft stop but the aircraft will no longer pitch up. This indicates the aircraft is stalled.

Hmmmmm !That's the quickest syllogism I've ever read in aviation !
No, "stall" refers to a completely disturbed airflow state over an airfoil and as such an alpha that's past alpha max, and not to the effect of a device that would prevent the aerodynamics phenomenon to happen.

[FE Hoppy]

No, "stall" refers to a completely disturbed airflow state over an airfoil and as such an alpha that's past alpha max, and not to the effect of a device that would prevent the aerodynamics phenomenon to happen.

Hmmm...... not according to the regulation by which all modern aircraft are certified.

I know exactly what you mean by the classic definition but we now have FBW systems which prevent it happening. Even before FBW if an aeroplane had stall characteristics which were no deemed appropriate a stick pusher was used to prevent the aircraft from reaching the classical "stall".

[DC-ATE]

Even before FBW if an aeroplane had stall characteristics which were no deemed appropriate a stick pusher was used to prevent the aircraft from reaching the classical "stall".

And just what would those "characteristics" be? The 737 did not have a stick pusher and yet could stall.

[Lemurian]

FE Hoppy
Therefore if I'm at a speed lower than that required to maintain 1g flight I am by definition stalling.
That definition applies to a straight and level flight.
By definition, in the descent equation, weight is higher than the produced lift, at a reduced Cl, meaning a smaller α.

not according to the regulation by which all modern aircraft are certified.

I know exactly what you mean by the classic definition but we now have FBW systems which prevent it happening. Even before FBW if an aeroplane had stall characteristics which were no deemed appropriate a stick pusher was used to prevent the aircraft from reaching the classical "stall".

There is a difference between ”aerodynamic stall” and “stall recognition” and even more with "stall protection", of which the stick pusher is one.
3.3.2 DEFINITION OF STALL SPEED
“The stalling speed, if obtainable, or the minimum steady speed, in knots (CAS), at
which the airplane is controllable with.... (the words that follow describe the required
configuration).”
- FAR Part 23.45

“The stall speed (equivalent airspeed) at 1 g normal to the flight path is the highest
of the following:
1. The speed for steady straight flight at CLmax (the first local maximum of lift
coefficient versus which occurs as CL is increased from zero).
2. The speed at which uncommanded pitching, rolling, or yawing occurs.
3. The speed at which intolerable buffet or structural vibration is encountered.”
- MIL-STD-1797A

From a test pilot’s perspective, the task is to investigate how much lift potential can
be exploited for operational use, without compromising aircraft control in the process. The
definition of stall speed comes from that investigation.
The discussion of minimum speed includes the notion of maximum lift coefficient
(CLmax). To maintain lift in a controlled deceleration at 1 g, the lift coefficient (CL)
increases as the dynamic pressure decreases (as a function of velocity squared). This
increase in lift coefficient is provided by the steadily increasing during the deceleration.
At some point in the deceleration the airflow over the wing separates, causing a reduction
of lift. The lift coefficient is a maximum at this point, and the corresponding speed at these
conditions represents the minimum flying speed.
The speed corresponding to CLmax may not be a reasonable limit. Any other
potential limitations may prescribe a minimum useable speed which
is higher than the speed corresponding to CLmax. The higher speed may be appropriate due
to high sink rate, undesirable motions, flying qualities, or control effectiveness limits.
Influence of the separated flow on the empennage may cause instabilities, loss of control,
or intolerable buffeting. Any of these factors could present a practical minimum airspeed
limit at a lift coefficient less than the CLmax potential of the airplane. In this case, the classic
stall is not reached and a minimum useable speed is defined by another factor.

[FE Hoppy]

cs25-201, 203 and 207.

an unacceptable characteristic might be for example a tendency to pitch up.

A stick pusher is not required if the aeroplane meets all the requirements as quoted above.

[FE Hoppy]

“The stall speed (equivalent airspeed) at 1 g normal to the flight path is the highest
of the following:
1. The speed for steady straight flight at CLmax

Your quote.

Isn't this where i came in?

[fergineer]

G'day Hoppy.......mixing it with the two winged master race whatever next........keep at it my son dont let them wear you down.
Regards from the Kiwi land

[Lemurian]

FE Hoppy
You can take whatever definition of "stalling speed" you can, from any certification authority, you still cannot decide all by yourself that it describes the actual phenomenon called "stall" which is caused by complete airflow separation over the upper wing surface, i.e past the Clmax alpha, and is the start of uncontrolled flight.
For FBW airliners, the stall cannot be demonstrated, therefore the definition for stalling speed is taken from a spread of speeds, on a level flight (1 g) and during a descent (n< 1g).
The difference between certification definition and real life can be described with the example of that MD-82 that crashed uncontrolled in South America.
For a pilot, the recovery techniques from an actual aerodynamic full stall and an FBW airplane in "alpha prot" situation are very different, by some order of magnitude.
But I guess this discussion is about two different perspectives.

A stick pusher is not required if the aeroplane meets all the requirements as quoted above.
Tell that to Boeing and the UK CAA about the 727 certification (which ,in a slanted way proves my point about certification and handling perspectives).

[FE Hoppy]

For a pilot, the recovery techniques from an actual aerodynamic full stall and an FBW airplane in "alpha prot" situation are very different, by some order of magnitude.
But I guess this discussion is about two different perspectives.

I agree. The point is that for the pilot there must be a clear definition in both protected and unprotected modes of what is considered a stall and what the apropriate recovery technique is for each. The authorities require both in any training program for an aircraft with protections.

[flyingflatfour]

By no means a "large" airliner, but the good old BAe-146 and AVRO RJ (last one produced in 2002) have unpowered, cable-controlled ailerons and elevators (using servo tabs) together with hydraulically powered roll spoilers and rudder.

You actually feel that you're moving the tab in the first half of the wheel deflection and then the whole tab + control surface in the second half (much heavier).

If you order too sharp a roll order you can even feel the downwing aileron tab being stalled for a second, a little bit like a car when you oversteer it ;-)

Now flying the A320 series, I do appreciate the full back stick procedure - it's simple and it works. And with EGPWS I guess you would never need more than 2,5G, would you ?

[DC-ATE]

Not sure how one is supposed to "end" one of these topics, but according to one, Lemurian, I didn't have the "nerve" to do so.

So, Mr/Mrs Lemurian, consider this ended.:bored: