I have a bit of a unique question, and can't seem to find the answer anywhere else. Stumbled across this forum, and was hoping some of you would know.

As I'm sure you're aware, with the two largest airliner manufactures, Boeing and Airbus, there seems to be a disagreement on the philosophy of automation - whether the flight computers or the pilot should have final say in aircraft inputs. Boeing tends to allow pilots this final say, and the computers will not prevent pilot inputs beyond certain parameters, while Airbus's aircraft have systems in place to prevent the pilot from making erroneous inputs.

My question is, what is the philosophy with some of the smaller jet aircraft, including private and regional, such as Honda, Embraer, Bombardier, etc. Do they err on the side of computer > pilot or visa versa?

Interesting question to me as this seems to be a big argument with the A vs B people, but I'd like to know how the other manufacturers compare. Thanks in advance!

CaptnSnow71 wrote:

I have a bit of a unique question, and can't seem to find the answer anywhere else. Stumbled across this forum, and was hoping some of you would know.

As I'm sure you're aware, with the two largest airliner manufactures, Boeing and Airbus, there seems to be a disagreement on the philosophy of automation - whether the flight computers or the pilot should have final say in aircraft inputs. Boeing tends to allow pilots this final say, and the computers will not prevent pilot inputs beyond certain parameters, while Airbus's aircraft have systems in place to prevent the pilot from making erroneous inputs.

My question is, what is the philosophy with some of the smaller jet aircraft, including private and regional, such as Honda, Embraer, Bombardier, etc. Do they err on the side of computer > pilot or visa versa?

Interesting question to me as this seems to be a big argument with the A vs B people, but I'd like to know how the other manufacturers compare. Thanks in advance!

I loved asking this questionon of the manufacturers at NBAA shows. most seemed to fall in between the two, being more restrictive than Boeing but not as restrictive as Airbus. A Gulfstream engineer I spoke to during the G650's introduction did openly favor Boeing. When I asked him about the plane's FBW (without mentioning either of the big 2), on his own he described it as the "Boeing system".

here are some articles with more info:

http://www.flyingmag.com/aircraft/jets/ ... ion#page-8
http://www.propilotmag.com/archives/201 ... pe_p1.html

With the exception of the C series, most are like Boeing.

Thanks for the replies! That second article was some good stuff. I honestly would have figured it would be the opposite.

CaptnSnow71 wrote:

I have a bit of a unique question, and can't seem to find the answer anywhere else. Stumbled across this forum, and was hoping some of you would know.

As I'm sure you're aware, with the two largest airliner manufactures, Boeing and Airbus, there seems to be a disagreement on the philosophy of automation - whether the flight computers or the pilot should have final say in aircraft inputs. Boeing tends to allow pilots this final say, and the computers will not prevent pilot inputs beyond certain parameters, while Airbus's aircraft have systems in place to prevent the pilot from making erroneous inputs.

You're making the same mistake as many who confuse fly by wire ( and control laws that potentially come with it) and automation (how a pilot chooses to fly the aircraft).

Boeing aircraft are every bit as automated as airbus aircraft.

Where control laws are concerned, the general trend is towards a more protected aircraft envelope. Both airbus and boeing allow you to remove those protections if need be.

CaptnSnow71 wrote:

I have a bit of a unique question, and can't seem to find the answer anywhere else. Stumbled across this forum, and was hoping some of you would know.

As I'm sure you're aware, with the two largest airliner manufactures, Boeing and Airbus, there seems to be a disagreement on the philosophy of automation - whether the flight computers or the pilot should have final say in aircraft inputs. Boeing tends to allow pilots this final say, and the computers will not prevent pilot inputs beyond certain parameters, while Airbus's aircraft have systems in place to prevent the pilot from making erroneous inputs.

My question is, what is the philosophy with some of the smaller jet aircraft, including private and regional, such as Honda, Embraer, Bombardier, etc. Do they err on the side of computer > pilot or visa versa?

Interesting question to me as this seems to be a big argument with the A vs B people, but I'd like to know how the other manufacturers compare. Thanks in advance!

It's a big argument among fans and some pilots, but I don't think the operators care that much. The majority of airline pilots care about pay, rosters and lifestyle much more than which plane they fly.

The old cliche that Boeing allows the pilots the final say and Airbus allows the computers the final say seems to me a massive oversimplification of the complexities involved. No, Airbus pilots don't "argue with the computers" and no, Boeing pilots don't "handle things manually". In both aircraft pilots work with the systems to solve problems and manage emergencies. The systems support the pilots. They don't either "take over" or "get out of the way". Airbus and Boeing systems differ in quite a few nuances, but they both achieve safe and efficient flying if managed by well trained and knowledgeable pilots.

IMHO, given modern aircraft flight controls perhaps the discussion is becoming a bit academic. Assume an upset, say excessive bank angle. By the time you get to the point where the Airbus flight control system would prevent further inputs (67 degrees bank), in a Boeing you'd be fighting the aircraft pretty hard. It won't stop you but it will make further inputs much harder. Hint hint, says the Boeing. You shouldn't be doing this. There isn't a "hard stop" but the message to the pilot is the same. Either way, if you get to that point the pilots have most likely done something wrong quite a while back.

Chaostheory wrote:

Where control laws are concerned, the general trend is towards a more protected aircraft envelope. Both airbus and boeing allow you to remove those protections if need be.

Semantics, perhaps, but Airbus doesn't really "allow" you to remove those protections, as in give you permission. You can do it by disabling some computers, but it is in no way an approved or recommended procedure in line flying. The only situation where I can think of it being approved is in the simulator for training with degraded flight control laws.

Starlionblue wrote:

CaptnSnow71 wrote:

I have a bit of a unique question, and can't seem to find the answer anywhere else. Stumbled across this forum, and was hoping some of you would know.

As I'm sure you're aware, with the two largest airliner manufactures, Boeing and Airbus, there seems to be a disagreement on the philosophy of automation - whether the flight computers or the pilot should have final say in aircraft inputs. Boeing tends to allow pilots this final say, and the computers will not prevent pilot inputs beyond certain parameters, while Airbus's aircraft have systems in place to prevent the pilot from making erroneous inputs.

My question is, what is the philosophy with some of the smaller jet aircraft, including private and regional, such as Honda, Embraer, Bombardier, etc. Do they err on the side of computer > pilot or visa versa?

Interesting question to me as this seems to be a big argument with the A vs B people, but I'd like to know how the other manufacturers compare. Thanks in advance!

It's a big argument among fans and some pilots, but I don't think the operators care that much. The majority of airline pilots care about pay, rosters and lifestyle much more than which plane they fly.

The old cliche that Boeing allows the pilots the final say and Airbus allows the computers the final say seems to me a massive oversimplification of the complexities involved. No, Airbus pilots don't "argue with the computers" and no, Boeing pilots don't "handle things manually". In both aircraft pilots work with the systems to solve problems and manage emergencies. The systems support the pilots. They don't either "take over" or "get out of the way". Airbus and Boeing systems differ in quite a few nuances, but they both achieve safe and efficient flying if managed by well trained and knowledgeable pilots.

IMHO, given modern aircraft flight controls perhaps the discussion is becoming a bit academic. Assume an upset, say excessive bank angle. By the time you get to the point where the Airbus flight control system would prevent further inputs (67 degrees bank), in a Boeing you'd be fighting the aircraft pretty hard. It won't stop you but it will make further inputs much harder. Hint hint, says the Boeing. You shouldn't be doing this. There isn't a "hard stop" but the message to the pilot is the same. Either way, if you get to that point the pilots have most likely done something wrong quite a while back.

Chaostheory wrote:

Where control laws are concerned, the general trend is towards a more protected aircraft envelope. Both airbus and boeing allow you to remove those protections if need be.

Semantics, perhaps, but Airbus doesn't really "allow" you to remove those protections, as in give you permission. You can do it by disabling some computers, but it is in no way an approved or recommended procedure in line flying. The only situation where I can think of it being approved is in the simulator for training with degraded flight control laws.

The point is the ability to degrade the laws and remove the limits is there if need be even if it requires button pushing unlike the Boeings. There have been a number of instances where airbus crews have done just that when the protections have activated when unwanted. I doubt anyone would disagree with the unapproved actions (at the time) of the Lufthansa crew (A330/A340?) who were required to do so.

In my question, I simplified the Boeing vs Airbus example to get the point across, as my question was really regarding the flight envelope protection on smaller aircraft. I'm aware that both Boeing and Airbus aircraft of similar era are equally automated, and I know that Boeing's aircraft make control input much more difficult beyond certain parameters.

Let's take your 67 degrees of bank example - as you said, the Boeing's flight controls will stiffen up, but in the Airbus you are not allowed this sort of input at all. Albeit very, very rare, there may be circumstances where this sort of input may be necessary. There have been cases that show the value of both systems.

Wasn't intending this to turn into a A vs B thread, I was just genuinely curious about how other manufacturers handle this philosophical disagreement. Regardless of the level of automation, there is no arguing that they are two very different systems.

As I mentioned above, I don't think this is a philosophical disagreement. I think the disagreement is much more alive in the minds of the fans than in the minds of the designers. As Airbus and Boeing have both stated, they "don't compete on safety."

Chaostheory and CaptnSnow71. You both mention cases in which the protections were better off deactivated. I'm happy to be proven wrong, but please state specific examples.

Which LH crew do you speak of, Chaostheory?

Starlionblue, I think Chaosteory means this one:
http://avherald.com/h?article=47d74074
A321 with 2 switched off ADIRS's to bring it into alternate law, as one of the protections was active due to 2 blocked AoA sensors.

Starlion, the two major examples would be China Air 006 and US Air 1549. 006 Would not have been able to recover if the crew had not been able to recover from the dive by stressing the aircraft beyond it's design limitations (and therefore far beyond the standard flight envelope). 1549 may have stalled on "final" over the Hudson without alpha max protection and may have lead to a very different result.

On the 777 and 787, where Boeing does implement "soft limit" envelope protection, I guess I would agree that it's not a *major* disagreement on philosophy, and I'm certainly not saying either one is compromising on safety. Just different theories. I suppose where I think the major differences lay is in the overall design of the flight deck - independently moving sidesticks vs yokes, autothrottle does or does not move the physical throttle, etc. We're getting off topic here, but I guess I was taking more into account than just flight envelope protection when I said "philosophical differences".

Where did you find that term "soft limit" in a Boeing FCOM, FCTM or CSID?

My only objection to 'hard limits' is from an engineering standpoint there are always tolerances to be considered. All the sensors that are used to determine stall speed, for instance, have manufacturing tolerances, tolerances when installed on the airplane, aging, temperature drift, etc. I doubt very seriously if a manufacturer would set a stall limit at 120 mph if that was the reality for a given set of plane configurations. A margin above that would be added considering tolerances and other things. Using a few mph of that margin could be useful in extreme conditions. Every time I see that Airbus flying into the tops of the trees, I wonder if another small increase in pitch angle would have allowed him to clear them.

I remember reading that a study was done regards the Delta L-1011 that crashed in Dallas after flying into the windshear. It basically said if they had overridden the stick shaker/pusher they would have cleared the road because of the stall margin built into the protection.

I fully agree that protections are very beneficial even though they should never be activated in normal flight. It would be interesting to know if any record is maintained of protection activation in the absence of an accident.

airtechy wrote:

My only objection to 'hard limits' is from an engineering standpoint there are always tolerances to be considered. All the sensors that are used to determine stall speed, for instance, have manufacturing tolerances, tolerances when installed on the airplane, aging, temperature drift, etc. I doubt very seriously if a manufacturer would set a stall limit at 120 mph if that was the reality for a given set of plane configurations. A margin above that would be added considering tolerances and other things. Using a few mph of that margin could be useful in extreme conditions. Every time I see that Airbus flying into the tops of the trees, I wonder if another small increase in pitch angle would have allowed him to clear them.

I remember reading that a study was done regards the Delta L-1011 that crashed in Dallas after flying into the windshear. It basically said if they had overridden the stick shaker/pusher they would have cleared the road because of the stall margin built into the protection.

I fully agree that protections are very beneficial even though they should never be activated in normal flight. It would be interesting to know if any record is maintained of protection activation in the absence of an accident.

There isn't.

I wonder if their activation is recorded on the QAR's?

airtechy wrote:

I wonder if their activation is recorded on the QAR's?

Yes they would be recorded. But it would be up to the operator on how this information is handled. Some Asian and ME carriers have a very robust oversight programs as witnessed in the recent EK, 777 accident.

I don't know that much about Boeing protections, but I think in the cases below modern Boeings would have handled the situation similarly to modern Airbuses (assuming the flight crews operate in accordance with proper procedures). The purpose of the protections in the same. Would be interested to hear from Boeing pilots about this.

TOGA10 wrote:

Starlionblue, I think Chaosteory means this one:
http://avherald.com/h?article=47d74074
A321 with 2 switched off ADIRS's to bring it into alternate law, as one of the protections was active due to 2 blocked AoA sensors.

Thanks for the reference. First off, that is an approved procedure. Secondly, the purpose of the exercise isn't so much to degrade the flight control law as to remove spurious inputs. Degradation to Alternate Law is a side effect.

CaptnSnow71 wrote:

Starlion, the two major examples would be China Air 006 and US Air 1549. 006 Would not have been able to recover if the crew had not been able to recover from the dive by stressing the aircraft beyond it's design limitations (and therefore far beyond the standard flight envelope). 1549 may have stalled on "final" over the Hudson without alpha max protection and may have lead to a very different result.

On the 777 and 787, where Boeing does implement "soft limit" envelope protection, I guess I would agree that it's not a *major* disagreement on philosophy, and I'm certainly not saying either one is compromising on safety. Just different theories. I suppose where I think the major differences lay is in the overall design of the flight deck - independently moving sidesticks vs yokes, autothrottle does or does not move the physical throttle, etc. We're getting off topic here, but I guess I was taking more into account than just flight envelope protection when I said "philosophical differences".

Air China 006. You could argue that on an Airbus, the upset might not have happened. However assuming it did, you'd have been in Abnormal Alternate Law, which has only load factor protection in pitch and direct control of roll. Ideal for recovering from an upset as you will be able to apply any control input up to the maximum G limits of the aircraft. Yes, Flight 006 overstressed the airframe, but that means risking breakup. Aerodynamicall, going beyond the G limits in an airliner probably means you're stalling control surfaces, meaning the recovery is less than optimal.

US Air 1549. As you say Alpha Max protected the crew from a stall. Thus they were able to ditch wings level. Similar to the Mulhouse crash.

airtechy wrote:

My only objection to 'hard limits' is from an engineering standpoint there are always tolerances to be considered. All the sensors that are used to determine stall speed, for instance, have manufacturing tolerances, tolerances when installed on the airplane, aging, temperature drift, etc. I doubt very seriously if a manufacturer would set a stall limit at 120 mph if that was the reality for a given set of plane configurations. A margin above that would be added considering tolerances and other things. Using a few mph of that margin could be useful in extreme conditions. Every time I see that Airbus flying into the tops of the trees, I wonder if another small increase in pitch angle would have allowed him to clear them.

I remember reading that a study was done regards the Delta L-1011 that crashed in Dallas after flying into the windshear. It basically said if they had overridden the stick shaker/pusher they would have cleared the road because of the stall margin built into the protection.

I fully agree that protections are very beneficial even though they should never be activated in normal flight. It would be interesting to know if any record is maintained of protection activation in the absence of an accident.

You have a point in that tolerances mean there might be some slim performance buffer to be used. However in that performance buffer any upset including gusts which the crew has no control over may lead to stall etc. Realistically, leaving the performance buffer in is more likely to protect the passengers if you count the total number of incidents when the crew operates close to the performance limits. One example is windshear. If you're holding full backstick to climb out of windshear, would you rather be 5 knots above the actual limit, or at the actual limit where any slight sideways gust might lead you to drop a wing dramatically?

Regarding tops of trees, low speed protection meant the plane crashed into them wings level and in controlled flight. With a smaller margin, the crash might have been with a bank angle, resulting in cartwheeling and a higher death toll.

Protections do activate in normal operations from time to time. An example is low speed protections when encountering mountain waves in the cruise.

Starlionblue wrote:

Air China 006. You could argue that on an Airbus, the upset might not have happened. However assuming it did, you'd have been in Abnormal Alternate Law, which has only load factor protection in pitch and direct control of roll. Ideal for recovering from an upset as you will be able to apply any control input up to the maximum G limits of the aircraft. Yes, Flight 006 overstressed the airframe, but that means risking breakup. Aerodynamicall, going beyond the G limits in an airliner probably means you're stalling control surfaces, meaning the recovery is less than optimal.

US Air 1549. As you say Alpha Max protected the crew from a stall. Thus they were able to ditch wings level. Similar to the Mulhouse crash.

Well I'm certainly not an expert, and may not fully understand the nuances in the Airbus system and will have to do more research on that. That being said, regardless of the danger, what other choice did flight 006 have? Risk breaking up, or certainly slam into the ground. A long shot is better than nothing, and in this case, it worked out best case scenario. Not to say that would always be the case.

Capt. Snow please tell us where you found this reference as otherwise this is all Voodoo stuff. I cannot find any reference to this term I'n any MBF document becauseI don't think any such term exists?

Where did you find that term "soft limit" in a Boeing FCOM, FCTM or CSID?

CaptnSnow71 wrote:

Starlionblue wrote:

Air China 006. You could argue that on an Airbus, the upset might not have happened. However assuming it did, you'd have been in Abnormal Alternate Law, which has only load factor protection in pitch and direct control of roll. Ideal for recovering from an upset as you will be able to apply any control input up to the maximum G limits of the aircraft. Yes, Flight 006 overstressed the airframe, but that means risking breakup. Aerodynamicall, going beyond the G limits in an airliner probably means you're stalling control surfaces, meaning the recovery is less than optimal.

US Air 1549. As you say Alpha Max protected the crew from a stall. Thus they were able to ditch wings level. Similar to the Mulhouse crash.

Well I'm certainly not an expert, and may not fully understand the nuances in the Airbus system and will have to do more research on that. That being said, regardless of the danger, what other choice did flight 006 have? Risk breaking up, or certainly slam into the ground. A long shot is better than nothing, and in this case, it worked out best case scenario. Not to say that would always be the case.

While the crew of China Airlines 006 saved the aircraft, perhaps with load limit protection the recovery could have been done more efficiently and rapidly, since the crew would know the structure would not potentially fail regardless of their actions. One less thing to worry about.

The philosophy is that protections are there to assist the crew, not hinder them from safely operating or recovering.

(Correction to earlier post. It was China Airlines, not Air China.)

BravoOne wrote:

Capt. Snow please tell us where you found this reference as otherwise this is all Voodoo stuff. I cannot find any reference to this term I'n any MBF document becauseI don't think any such term exists?

Where did you find that term "soft limit" in a Boeing FCOM, FCTM or CSID?

Soft limits is a term pretty widely used to describe a system of flight envelope protection that does provide 'limitations' to the aircraft, but does not outright prohibit the pilot from overriding these limits. For example, in the FBW Boeing aircraft, the bank and pitch angle are limited to a certain point that the controls become much stiffer to discourage pilots from making these inputs unless "necessary" (which is what the debate is about), where the pilot is physically capable of pushing the aircraft outside of it's normal limits without having to disable any on board systems. In the Airbus, the limits are "hard", as regardless of how much the pilot wants to bank the aircraft beyond 67 degrees, it simply wont let it. At least that's my understanding. As previously stated, I'm not an expert and don't claim to be.

I have no doubt you haven't found the term in any official document because it's not an official term. It still gets the point across. I think this article explains it pretty well https://www.skybrary.aero/index.php/Fly-By-Wire (skip down a bit).

" One example is windshear. If you're holding full backstick to climb out of windshear, would you rather be 5 knots above the actual limit, or at the actual limit where any slight sideways gust might lead you to drop a wing dramatically?"

The example I gave..the Delta flight...was an actual example of windshear. If a crash was inevitable, I would certainly want to use the 5 knots...especially off airport near the ground. I really doubt the margin is as low as 5 knots on any airplane....either Boeing or Airbus. Seems way too close.

Also, how much is the bank angle limited as the stall speed is approached on an Airbus? Are you saying it tapers down to zero degrees? Interesting...

airtechy wrote:

" One example is windshear. If you're holding full backstick to climb out of windshear, would you rather be 5 knots above the actual limit, or at the actual limit where any slight sideways gust might lead you to drop a wing dramatically?"

The example I gave..the Delta flight...was an actual example of windshear. If a crash was inevitable, I would certainly want to use the 5 knots...especially off airport near the ground. I really doubt the margin is as low as 5 knots on any airplane....either Boeing or Airbus. Seems way too close.

Also, how much is the bank angle limited as the stall speed is approached on an Airbus? Are you saying it tapers down to zero degrees? Interesting...

The bank angle limit remains the same, except in high speed protection. However increased wing loading leads to an increase in ALPHAmax, as shown by the barberpole moving up the speedtape. If you bank more, you get increased wing loading, so if you're at the limit, the limit moves up and the nose goes down to maintain the higher ALPHAmax AoA.

Somewhat similar to the Boeing "soft limits" is that if you let go of the stick at 0-33 degrees angle of bank, the angle is maintained. If you go beyond 33 degrees, you must hold the stick or the bank will decrease to 33 degrees and stay there.

Regarding a case such as Delta, it is a tricky one. You'd want to use the 5 knots, but what if there was a gust which led to a loss of control (or in the case of Airbus, hitting the AoA limit and not being able to climb). Rather hit the ground in control or potentially climb out?

CaptnSnow71 wrote:

BravoOne wrote:

Capt. Snow please tell us where you found this reference as otherwise this is all Voodoo stuff. I cannot find any reference to this term I'n any MBF document becauseI don't think any such term exists?

Where did you find that term "soft limit" in a Boeing FCOM, FCTM or CSID?

Soft limits is a term pretty widely used to describe a system of flight envelope protection that does provide 'limitations' to the aircraft, but does not outright prohibit the pilot from overriding these limits. For example, in the FBW Boeing aircraft, the bank and pitch angle are limited to a certain point that the controls become much stiffer to discourage pilots from making these inputs unless "necessary" (which is what the debate is about), where the pilot is physically capable of pushing the aircraft outside of it's normal limits without having to disable any on board systems. In the Airbus, the limits are "hard", as regardless of how much the pilot wants to bank the aircraft beyond 67 degrees, it simply wont let it. At least that's my understanding. As previously stated, I'm not an expert and don't claim to be.

I have no doubt you haven't found the term in any official document because it's not an official term. It still gets the point across. I think this article explains it pretty well https://www.skybrary.aero/index.php/Fly-By-Wire (skip down a bit).

Thats pretty much what I figured. I am very familiar with Boeing FBW technology and design concepts, not so much AB. I have never heard anyone at The Boeing Company use that term so when someone starts tossing these terms around. the waters get murky real fast and as Boeing has learned can have consequences as in "auto throttle wakeup". Skybray.sero?

Just to followup there's a secondary link from the original page I posted, it goes far more in depth on the differences between the two systems. https://www.skybrary.aero/index.php/Flight_Control_Laws

Starlionblue wrote:

US Air 1549. As you say Alpha Max protected the crew from a stall. Thus they were able to ditch wings level. Similar to the Mulhouse crash.

Can I ask a question about that alpha protection thing? Maybe somebody here knows.

The US Air 1549 airplane didn't achieve max alpha because the airplane attenuated nose-up pitch commands after dropping below alpha protection speed into alpha-protection mode (he was full back stick, but the airplane wasn't giving him max alpha), and additionally there was an anti-phugoid thing in the software also attenuating the full-back-stick command. The net effect was splashdown angle of attack about 4 degrees below alpha max, even though he was full back stick.

Is this pitch command attenuation incorporated in order to avoid accidentally exceeding critical angle of attack because of rapid pitch changes and inertia, so you don't blow past max alpha in rapid maneuvering?

Very good question. I don't know. However it would make sense.

However there is a pitch down bias introduced just prior to touchdown. Don't know if that happens when you ditch with the gear up, though.