soaringadi
Posts: 452
Joined: Fri Apr 30, 2004 4:56 pm

Fly-by-wire... Blessing Or A Curse?

Mon Dec 27, 2004 9:59 pm

Is technology starting to cross the line between helpful and dangerous ? Is it good or bad to have too much tecnology on our hands.

As we all know that fly-by-wire systems eliminate the "natural feel" of the controls and give you that "fake feeling" I know many will opose me on my idead but try this thing: If you are in a car that has a power boosted steering (for example a Lexus or Toyota) and you drive it. Now if you drive a Bmw (which has a minimal power steering and it gives you that natural feel which puts you "in contact" with the road) you will notice the increase in your confidence levels in driving the car and you will be swapping lanes like a pro.
(plz. no offense intended to any car companies or anyone who drives them).

So coming back to the topic the joystick that Airbus' have or the controls in the T7. Don't these give a fake feel opposed to the natural ? So do you think this is kind of dangerous or is it a blessing to have this kind of technology.

Ps: I haven't flown any of these so I don't exactly know how each airplane feels.

I'm interested about what you guys think

l / out..
 Smile





If it ain't Boeing, I'm not going !
 
pilotpip
Posts: 2838
Joined: Fri Sep 19, 2003 3:26 pm

RE: Fly-by-wire... Blessing Or A Curse?

Mon Dec 27, 2004 10:38 pm

Aircraft have had hydraulically boosted controls for years. Those don't have any "feel" as you mention so most use a system that compensates and changes the pressures the pilot will feel on the yoke and pedals respectively. The 777 has this as well. Talking about the systems on the Airbus system versus the Boeing system is apples to oranges as they use different philosophies and design logic in their aproaches. Both have their pros and cons, but I think the records of the current FBW aircraft are proof that they are safe systems. Also, consider that nearly every new aircraft currently being designed will encorporate digital interfaces.

Airliners are rarely flown by hand. An autopilot keeps the aircraft in a much more comfortable attitude during cruise, and is much more accurate in maintaining airspeeds and altitudes than any pilot ever could. Also, when you get in a plane that big, you fly by the numbers. You fly airspeeds, and by your instruments, not by the 'seat of your pants' like you would in a cessna. This is a very high workload environment and it's much safer for a pilot to be monitoring systems while handling radios, navigation, etc rather than doing this and hand flying. You'd be spilling your drink.
This was a problem that was faced by the early jet pilots and accounts for many early accidents in aircraft such as the 727.

Fly by wire systems have nearly 30 years under their belt now and their reliability has been proven. There are many built in redunancy systems and I think that as a result, a worst case scenario like UA 232 is completely elimnated as if a wire is severed, there are other routes for the information to travel and you don't have the risk of the ones and zeros draining from the system.
DMI
 
User avatar
HAWK21M
Posts: 30037
Joined: Fri Jan 05, 2001 10:05 pm

RE: Fly-by-wire... Blessing Or A Curse?

Mon Dec 27, 2004 11:15 pm

Isn't Artifical Feel provided in these Jets to eliminate the problem of overstressing the Control surfaces.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
User avatar
Starlionblue
Posts: 19170
Joined: Fri Feb 27, 2004 9:54 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 12:06 am

As we all know that fly-by-wire systems eliminate the "natural feel" of the controls and give you that "fake feeling"

As PilotPip says, they don't really. The "natural feel" you speak of was eliminated many decades before with all the power assistance, trim tabs and so on.

FBW is hardly new, and will continue to bring us safely to our destinations.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
garnetpalmetto
Posts: 5352
Joined: Tue Oct 21, 2003 1:38 am

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 12:41 am

If fly-by-wire wasn't the way to go, I doubt the US military would have stuck with it in their premiere combat aircraft since the late 1970s. I doubt anyone can argue that few need an absolute "feel" for their aircraft like pilots of high performance combat aircraft. Yet pilots of the F-16, F/A-18, F/A-22, F-117, B-1, B-2, and C-17 have successfully flown their aircraft and fought with them with, as far as I can see, few if any complaints.
South Carolina - too small to be its own country, too big to be a mental asylum.
 
User avatar
Starlionblue
Posts: 19170
Joined: Fri Feb 27, 2004 9:54 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 12:52 am

Garnetpalmetto, thanks for that. And while we are at it, let's throw in the Su-37, Typhoon and Gripen, also FBW fighter aircraft.

The proof is in the pudding. Does Airbus FBW make aircraft less safe? Considering that no FBW Airbus has ever had a fatal accident due to mechanical or design faults, I don't see how one can make that argument.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
A340Driver
Posts: 94
Joined: Tue Nov 23, 2004 5:40 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 1:12 am

When the worst thing happens on the worst day, you are not going to survive a downburst in a 747 that you would survive in an A340.

Ask the passengers and crew of the Virgin 340 that nearly went in to the sea on short finals to HKG.

 
AAR90
Posts: 3140
Joined: Fri Jan 21, 2000 11:51 am

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 1:15 am

Airliners are rarely flown by hand.

Hmmm... all my airliner flights must be pretty rare then since every takeoff, virtually all climbs, most approaches and every landing is hand flown.

An autopilot keeps the aircraft in a much more comfortable attitude during cruise,

Not sure what you're trying to say here, but cruise attitude is dependent upon speed, weight & altitude... autopilot use has no role. OTOH, autopilot use in cruise makes the pilots' job much easier (reduced workload).

...and is much more accurate in maintaining airspeeds and altitudes than any pilot ever could.

Obviously you've not been flying the 738.  Laugh out loud Autothrottle control is horrible! Under normal conditions the autopilot will control altitude quite well (+/- 20 feet) for long periods of time, but in rough weather (+/- 100 feet) or for short periods of time a human is usually much better...especially when using the HUD --which expands the displays making even small deviations visible to the human pilot long before the autopilot attempts to make any correction. Which explains why AA's 738's are certified to CAT-III using HUD, but are not certified below 1800RVR using autopilots.

Is technology starting to cross the line between helpful and dangerous ? Is it good or bad to have too much tecnology on our hands.

Technology is neither good nor bad, it simply... IS. "Too much technology" by definition (you used the words "too much") is..."bad," but the point at which technology becomes "too much" will always remain in dispute.

IMHO one must differentiate between "Fly-By-Wire" and "Fly-By-Computer." FBW is simply the change from cable-pully control to electrical control. "FBC" places a computer between the pilot and the controls and limits what can occur to whatever the computer programmer has programmed the computer to do/allow. Anybody know of a computer program that hasn't been released for distribution that did not contain "bugs"??? Not an A v. B argument as ALL aircraft manufacturers use multiple computers for design, production, flight control, navigation, etc., etc., etc.
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
User avatar
Starlionblue
Posts: 19170
Joined: Fri Feb 27, 2004 9:54 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 1:16 am

Ask the passengers and crew of the Virgin 340 that nearly went in to the sea on short finals to HKG.

Sounds interesting, but I can't find details of it. What can you tell us?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
RayChuang
Posts: 8132
Joined: Sat Jun 24, 2000 7:43 am

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 1:17 am

The problem with FBW in the early days of A320 operations was that it was a major unknown at how well pilots would get acclimated with FBW systems and how safe FBW operated. As such, there were a number of unfortunate A320 crashes until the FBW system was properly tuned and pilots learned how to fly the plane properly.
 
DfwRevolution
Posts: 9246
Joined: Sat Jan 09, 2010 7:31 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 1:21 am

Ask the passengers and crew of the Virgin 340 that nearly went in to the sea on short finals to HKG.

I think it was EK and I think it was in JAB

Is technology starting to cross the line between helpful and dangerous ? Is it good or bad to have too much tecnology on our hands.

FBW is simply wonderful. It reduces the crew workload, it reduces the weight of the airplane, it is easier to maintain, it saves fuel by keeping the aircraft perfectly level through flight, ect.

It's important to remember that there have been far more accidents (or near-accidents) from control cable failure than there have been FBW failures. FBW is totally safe, and one of the great innovations to have gone mainstream in the last 15-20 years.
I have a three post per topic limit. You're welcome to have the last word.
 
User avatar
Starlionblue
Posts: 19170
Joined: Fri Feb 27, 2004 9:54 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 1:23 am

The problem with FBW in the early days of A320 operations was that it was a major unknown at how well pilots would get acclimated with FBW systems and how safe FBW operated. As such, there were a number of unfortunate A320 crashes until the FBW system was properly tuned and pilots learned how to fly the plane properly.


There is no difference in "tuning". The system behaves the same now as it did in the early days.

As for pilot training, accidents occured not because of interaction problems, but because pilots made mistakes, mistakes that would have been just as bad in a Boeing. Just because an aircraft has flight envelope protection doesn't make it immune to the laws of physics.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
RayChuang
Posts: 8132
Joined: Sat Jun 24, 2000 7:43 am

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 1:28 am

There is no difference in "tuning". The system behaves the same now as it did in the early days.

That's actually not true. After that unfortunate crash at Mulhouse in France during that demonstration flight in 1988 they had to change some of the FBW parameters to prevent a repeat of that accident.
 
User avatar
Starlionblue
Posts: 19170
Joined: Fri Feb 27, 2004 9:54 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 1:31 am

There is no difference in "tuning". The system behaves the same now as it did in the early days.

That's actually not true. After that unfortunate crash at Mulhouse in France during that demonstration flight in 1988 they had to change some of the FBW parameters to prevent a repeat of that accident.


I don't believe so but I may be wrong. What parameters were changed? There was nothing wrong with the aircraft at the time. 100% pilot error.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
aviopic
Posts: 2423
Joined: Sat Mar 13, 2004 7:52 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 3:23 am

If fly-by-wire wasn't the way to go, I doubt the US military would have stuck with it in their premiere combat aircraft since the late 1970s. I doubt anyone can argue that few need an absolute "feel" for their aircraft like pilots of high performance combat aircraft. Yet pilots of the F-16, F/A-18, F/A-22, F-117, B-1, B-2, and C-17 have successfully flown their aircraft and fought with them with, as far as I can see, few if any complaints

Yes i can argue with this quite easily  Laugh out loud
There is absolute no feel in the side stick of a fighter infect there is not even movement(other then a tiny bit) in a fighter side stick.
The only thing you do is applying pressure and that's it.

Willem
The truth lives in one’s mind, it doesn’t really exist
 
User avatar
Starlionblue
Posts: 19170
Joined: Fri Feb 27, 2004 9:54 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 3:28 am

Willem, I see your point. But the airplane is no less manoeuvrable, precise or reliable because of FBW or the sidestick.

[Edited 2004-12-27 19:30:44]

[Edited 2004-12-27 19:31:02]
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
aviopic
Posts: 2423
Joined: Sat Mar 13, 2004 7:52 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 3:39 am

Willem, I see your point. But the airplane is no less manoeuvrable, precise or reliable because of FBW or the sidestick.

Oh for sure not ! it is not even flyable with anything other then FBW.
Modern fighters like the F16 are unstable and would fall from the sky if they had any direct human input.
They can only be flown by and not with the help off computers.
There for should fighter and pax fbw not be compared, they are a complete different ball game.

Willem
The truth lives in one’s mind, it doesn’t really exist
 
User avatar
Starlionblue
Posts: 19170
Joined: Fri Feb 27, 2004 9:54 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 4:00 am

Oh for sure not ! it is not even flyable with anything other then FBW.
Modern fighters like the F16 are unstable and would fall from the sky if they had any direct human input.
They can only be flown by and not with the help off computers.
There for should fighter and pax fbw not be compared, they are a complete different ball game.


Well, I don't know. If we can build unstable fighters and make them flyable with FBW, surely FBW and the sidestick don't make airliners unsafe?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
aviopic
Posts: 2423
Joined: Sat Mar 13, 2004 7:52 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 4:08 am

For sure not. That is not what i meant to say.
See also this topic https://www.airliners.net/discussions/general_aviation/read.main/1877800/

Willem


[Edited 2004-12-27 20:28:32]
The truth lives in one’s mind, it doesn’t really exist
 
User avatar
Starlionblue
Posts: 19170
Joined: Fri Feb 27, 2004 9:54 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 4:17 am

Ok I get it. And now I'm just waiting for someone to bring up the 320 crash at Mulhouse.  Wink/being sarcastic
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 4:25 am

Having flown both military (F-16) and civilian (A-320) FBW, I would say it is a blessing.

Granted the control laws for both applications (civilian v. military) are quite different, the operation is similar.

For me the work load is reduced by a tremendous amount. I agree with AAR90 in that all my takeoffs, most of my climbs and descents and 99.9% of my landings are hand flown, but FBW makes it much easier. You don't have to worry about trim, and it's almost like point and shoot. Just set the ballpark pitch on the PFD and then it's minor corrections.

For the approach phase, I'd take FBW any day. If you're flying a 3degree ILS, then when you intercept the G/S just lower the nose by 3 degrees and that's it. On a conventional flight control, you lower it the same but there is additional trim requirement due to the change in power (744). So, in terms of work load the FBW, for me, wins.
Fly fast, live slow
 
aviopic
Posts: 2423
Joined: Sat Mar 13, 2004 7:52 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 4:34 am

You mean a 744 does not provide auto trim Phil ?
Anyway if that is the case it has not much to do with FBW or not.
Auto trim can just as easy be implemented on a cable system.

Willem

The truth lives in one’s mind, it doesn’t really exist
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 4:37 am

When you are "hand flying" the aircraft, there is no auto trim. The trim is all pilot input.

Fly fast, live slow
 
aviopic
Posts: 2423
Joined: Sat Mar 13, 2004 7:52 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 4:44 am

ok as i expected.
So when you want to perform an autoland no trimming is required and basically your work load is the same as on any Airbus i suppose ?

The truth lives in one’s mind, it doesn’t really exist
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 4:55 am

Not quite as there is autoland on both aircraft.

Auto land is when the aircraft is controlled by the autopilot and, normally, the auto throttles. In that situation, when an auto land is accomplished on the 744 or A320, the work load is the same.

However, when you are doing a manual landing in both aircraft, and for argument's sake, the auto throttles are off, for me, the FBW is much easier. Rarely, is there an approach where you are not making small corrections to power settings. With aircraft that have pylon mounted engines on the wing, the application or reduction of power will produce a pitch up or pitch down moment. In the 744, you have to trim to neutralize the yoke forces, with the 320 you don't. Just one less thing to worry about.
Fly fast, live slow
 
aviopic
Posts: 2423
Joined: Sat Mar 13, 2004 7:52 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 5:34 am

However, when you are doing a manual landing in both aircraft, and for argument's sake, the auto throttles are off.
Do i understand you correctly when i say you fly a manual approach with AT engaged normally ? (which is quite common) and the work load would still be the same ? In other words under normal circumstances there is no difference in work load between both systems ?

Haha i must drive you crazy which is not my intention though.
My point from the beginning was that the difference between the 2 systems is far less as some people seem to think and there is no point to be in favor or against one or the other.
Some people seem to think that with an control column present you have cables connected straight to the control surfaces and therefore really can "feel" the aircraft which is far from the reality, not even a Lockheed Constellation from 1948 it is done like that.
To sum up my point.
Both systems sidestick or control column are flown by computers(if AP AT Trim YD and so on are engaged), both provide feel by dedicated electronics, both control laws are more or less the same or can be implemented in the same way regardless of the system used.
And the main difference is that one can be flown completely manual(not really as you still want to have hydraulic and electrical support) and the way redundancy is dealt with.
The truth lives in one’s mind, it doesn’t really exist
 
Leskova
Posts: 5547
Joined: Wed Oct 08, 2003 3:39 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 5:38 am

Starlionblue, as far as I know you're right - the FBW wasn't changed after Mulhouse, but the autopilot annunciator panel: what the pilot had wanted to do was set a descent angle of 3.3 degrees, but what he did was set a descent speed in feet/minute: 3300 ft/min.

The design was changed so that the difference between angles and vertical speeds was more obvious.


As for the A340 that nearly went into the sea? DfwRevolution, I suspect you meant the EK A340 incident at JNB (JAB is "Jabiru" in Australia, and I know that EK doesn't fly there) - but that aircraft hardly went "into the sea": there's no amount of water anywhere near JNB, the nearest coast is either some 700-800km to the west (Mocambique) or almost 1000km to the south (around Durban)...

What did happen there was that the crew was using the sidestick-position indicator on the artificial horizon in a way that it was not meant to be used... not to mention that they were using it in a way that was against their training: they were trying to align the horizontal indicator with the displayed horizon (if I recall correctly) and thus ended up actually pushing the plane back down while it could have left the ground, had the controls only been used correctly.

Regards,
Frank
Smile - it confuses people!
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 5:48 am

Aviopic,

Depends on the airline. Some airlines, if you are hand flying the aircraft, you hand fly the throttles, you turn the auto throttle off. Other airlines, it makes no difference.

As a personal preference, if I hand fly the aircraft, then the auto throttles are off. In this case, FBW is less work since you're not having to make pitch trim changes with each change of the throttles.

As far as commercial aircraft go, I have only flown Boeings, 320 and the DC-10. None of the "conventional" aircraft have the flight control system you describe. I really am not familiar with what you're talking about. Unless you're talking about CWS (control wheel steering) which is like power steering for flight controls.
Fly fast, live slow
 
aviopic
Posts: 2423
Joined: Sat Mar 13, 2004 7:52 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 6:06 am

As far as commercial aircraft go, I have only flown Boeings, 320 and the DC-10. None of the "conventional" aircraft have the flight control system you describe. I really am not familiar with what you're talking about. Unless you're talking about CWS (control wheel steering) which is like power steering for flight controls.

Haha.... i am talking about "your" system from which i am quite sure can be found in the 744 you have flown.
And yes..... you have power steering if you want to call it like that which to my knowledge is present on every commercial airliner since the 40-ties or so.
Never mind though, this discussion should be in the technical forum area anyway.
The truth lives in one’s mind, it doesn’t really exist
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 6:08 am

Aviopic,

I can assure you in the normal "hand flown" mode all the pitch trim is manual. If you want you can contact me via my email and I'd be happy to continue this discussion.
Fly fast, live slow
 
RightWayUp
Posts: 80
Joined: Wed Oct 10, 2001 5:40 am

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 6:32 am

The incident A340 driver alludes to was a Virgin A340. Doubt you will find anything official! However the recovery manoeuvre was a glowing testament to FBW. Just pull full backstick and you will get max performance.
 
aviopic
Posts: 2423
Joined: Sat Mar 13, 2004 7:52 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 6:43 am

I can assure you in the normal "hand flown" mode all the pitch trim is manual. If you want you can contact me via my email and I'd be happy to continue this discussion.

I know Phil and i was not trying to proof you wrong, in manual mode trim is also manual on a system as can be found on a 744(and most others) where auto trim is a function of the AP and on an A3x a fuction of the FBW(semi manual or AP).
Thanks for the offer.

Willem

The truth lives in one’s mind, it doesn’t really exist
 
User avatar
Starlionblue
Posts: 19170
Joined: Fri Feb 27, 2004 9:54 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 9:05 am

Starlionblue, as far as I know you're right - the FBW wasn't changed after Mulhouse, but the autopilot annunciator panel: what the pilot had wanted to do was set a descent angle of 3.3 degrees, but what he did was set a descent speed in feet/minute: 3300 ft/min.

Hey Leskova. I knew that the annunciator panel was changed. However this was after the Strasbourg accident (http://aviation-safety.net/database/1992/920120-0.htm). Actually the new design was already being retrofitted. The accident simply hurried everyone up.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
A340Driver
Posts: 94
Joined: Tue Nov 23, 2004 5:40 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 5:57 pm

The Mulhouse A320 was attemtping to demonstrate Alpha Floor protection but this is inhibited at low level for landing. By the time this was realised, full thrust was manually applied and the 8 second spool up delay took the aircraft in to the trees.

The Virgin A340 at HKG was NOTHING to do with the EK JNB incident which has been correctly described above and was due to a total lack of training on the A340. I know the difference between JNB and HKG!

At HKG, A Virgin 340 experienced a downburst on short finals and was very nearly lost. I do not have the exact figures but I understand the aircraft came within feet of the sea during the recovery. The point of my post was that I don't believe anybody could have survived if this had been a 747 as I know I wouldn't be able to maintain Alpha Max manually as the Airbus does automatically.



 
User avatar
jumbojim747
Posts: 2426
Joined: Sat Oct 16, 2004 8:05 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 6:23 pm

The point of my post was that I don't believe anybody could have survived if this had been a 747
You may be right but i don't think the queen of the skies due to her large size in comparison to the 340 would be placed in that situation .
But then again the saying goes if it can happen it might.
On a wing and a prayer
 
A340Driver
Posts: 94
Joined: Tue Nov 23, 2004 5:40 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 6:40 pm

Are you serious? Are you saying that 'The Queen of the skies' is so big that it isn't subject to Windshear Downburst?

That sort of attitude causes accidents. A 747 is no match for the energy created by these situations.

I'll stick with a FBW in that situation thanks, and that includes a 777, so it's not a Boeing/Airbus/Size thing as you seem to infer it may be.

 
User avatar
Starlionblue
Posts: 19170
Joined: Fri Feb 27, 2004 9:54 pm

RE: Fly-by-wire... Blessing Or A Curse?

Tue Dec 28, 2004 11:36 pm

The Mulhouse A320 was attemtping to demonstrate Alpha Floor protection but this is inhibited at low level for landing. By the time this was realised, full thrust was manually applied and the 8 second spool up delay took the aircraft in to the trees.

The pilot disabled alpha floor protection as you say. But he did so consciously. The accident was caused by:
- Unplanned very low flyby.
- Unplanned runway used.
- Flyby under the level of surrounding trees.
- Aircraft altitude not stabilized at time of flyby, and still descending.
- Speed close to stall and still decreasing. The envelope protection was compensating by raising the nose.
The plane did not stall but there were are only two ways to increase speed: descending or increasing thrust. One was out due to altitude, the second was out due to approaching the trees. The spool up delay is quite normal for the engine type, and the aircraft and engines performed up to, and beyond, specifications.

It has been said many times on this forum but is worth repeating: THIS ACCIDENT WOULD MOST PROBABLY HAVE HAPPENED WITH ANY OTHER AIRCRAFT GIVEN HOW THE PILOT WAS HANDLING THE PLANE. The pilot thought that the Airbus control systems would protect him, but he apparently forgot that the laws of physics still apply.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
A340Driver
Posts: 94
Joined: Tue Nov 23, 2004 5:40 pm

RE: Fly-by-wire... Blessing Or A Curse?

Wed Dec 29, 2004 8:00 am

I did not say he disconnected Alpha Floor, I said he was attempting to demonstrate this protection. I wasn't aware it was possible to 'disable' Alpha Floor

Speed close to stall and still decreasing. The envelope protection was compensating by raising the nose

It is not possible to Stall Airbus family aircraft in the normal law. In normal law, protection would not raise the nose to compensate but would LOWER the nose to compensate






 
2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

RE: Fly-by-wire... Blessing Or A Curse?

Wed Dec 29, 2004 8:22 am

"The fact is, the plane did exactly what it was supposed to do." - John Lauber, V.P. of safety and technical affairs for Airbus, in reference to the Mulhouse A320 crash.


I found this quote in an online article awhile ago. I would have liked to hear him elaborate on it.


2H4
Intentionally Left Blank
 
User avatar
Starlionblue
Posts: 19170
Joined: Fri Feb 27, 2004 9:54 pm

RE: Fly-by-wire... Blessing Or A Curse?

Wed Dec 29, 2004 8:31 am

I did not say he disconnected Alpha Floor, I said he was attempting to demonstrate this protection. I wasn't aware it was possible to 'disable' Alpha Floor

The captain did so, and relied on the copilot to apply power. If he had not disabled Alpha Floor, engine thrust would have automatically increased as Alpha reached 15 degrees.


Speed close to stall and still decreasing. The envelope protection was compensating by raising the nose

It is not possible to Stall Airbus family aircraft in the normal law. In normal law, protection would not raise the nose to compensate but would LOWER the nose to compensate


Good point. My mistake. If the pilot had pulled up like this with Alpha Floor enabled, engine thrust would have been applied automatically and the nose would have been lowered, also automatically.


The pilot disabled a safety feature, and then proceeded to disregard not only the design features of the aircraft (if you've inhibited Alpha Floor protection, it can't protect you) but the laws of physics. If the plane is low and going downwards slowly, it will take a while to get out of the situation.


BTW I'm getting most of this from "Air Disasters: Volume 3" by Macarthur Job
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
A340Driver
Posts: 94
Joined: Tue Nov 23, 2004 5:40 pm

RE: Fly-by-wire... Blessing Or A Curse?

Wed Dec 29, 2004 6:00 pm

Ok, interesting. I can't think of a way of disconnecting Alpha Floor. It is not actually a fly by wire protection as such, it is an Auto Thrust Function.

It's all getting very technical!  Smile
 
aviopic
Posts: 2423
Joined: Sat Mar 13, 2004 7:52 pm

RE: Fly-by-wire... Blessing Or A Curse?

Wed Dec 29, 2004 6:54 pm

Ok, interesting. I can't think of a way of disconnecting Alpha Floor. It is not actually a fly by wire protection as such, it is an Auto Thrust Function.

It's all getting very technical!

Yes finally it is getting interesting.  Laugh out loud
To my best knowledge Alpha floor is a Ground Proximity Warning(enhanced these days) function by which i don't mean you are wrong.
The recovery that should follow is indeed an Auto Thrust Function which by itself is an Autopilot function on non FBW aircrafts.
AT can be switched on/off anytime GPWC not...... or at least the crew is not allowed to do so therefore this is on of the inputs monitored by the Flight Data Acquisition Unit(FDAU).

Willem
The truth lives in one’s mind, it doesn’t really exist
 
A340Driver
Posts: 94
Joined: Tue Nov 23, 2004 5:40 pm

RE: Fly-by-wire... Blessing Or A Curse?

Wed Dec 29, 2004 7:30 pm

Alpha Floor is an Auto Thrust function but it does not rely on Autothrust being armed or active.

Alpha floor is absolutely nothing to do with the GPWS.

FCOM 1.22.30:

'Alpha Floor protection is triggered when the FMGC receives a signal elaborated by the PRIMs'

It is automatically inhibited below 100ft, hence the problem.

If you have a reference in FCOM where you can switch off Alpha Floor then please let me know as I wasn't aware you could do this.

 
User avatar
Starlionblue
Posts: 19170
Joined: Fri Feb 27, 2004 9:54 pm

RE: Fly-by-wire... Blessing Or A Curse?

Thu Dec 30, 2004 12:21 am

It is automatically inhibited below 100ft, hence the problem.

Maybe Air Disasters Vol 3 is just unclear. It clearly says the pilot inhibited Alpha Floor. However since you say it is inhibited automatically below 100ft, the effect is the same.

BTW in a way this sort of helps my case about protection being more good than bad. Flying without protection can end badly.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Leskova
Posts: 5547
Joined: Wed Oct 08, 2003 3:39 pm

RE: Fly-by-wire... Blessing Or A Curse?

Thu Dec 30, 2004 4:16 am

I found this rather interesting link with regard to the accident in Mulhouse (I hope this is the right one and not, as above, the wrong accident):

http://www.cs.york.ac.uk/hise/safety-critical-archive/2002/0466.html

It includes comments from the pilot, Michel Asseline, about what errors were made.

The one point I found interesting was the altimeter discrepancy: the crew actually thought they were at 100ft while, in fact, they were at 30ft. Also, they didn't notice the difference by visual cues, because they were used to larger airports than the one they were overflying, so the visual cues they were getting from the ground gave them the impression that they were higher - while in fact everything on the ground was simply smaller.

And, on the issue of Alpha Floor, the report mentions this:

It should be noted that there was an important reason for disconnecting autothrust on this flight. The intended fly-over height was 100ft AGL at maximum AOA. If A/THR was enabled, alpha-floor would be activated and spoil the demonstration.


There's a lot more information on that site...

Regards,
Frank
Smile - it confuses people!
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Fly-by-wire... Blessing Or A Curse?

Thu Dec 30, 2004 4:32 am

It has been several years aince I have flown the 320. However, if I remember correctly, you can't inhibit Alpha protection. Even with the auto throttles disconnected you still have Alpha protection. Again, I am not so sure the accident books everyone is referring to are all that correct.
Fly fast, live slow
 
User avatar
Starlionblue
Posts: 19170
Joined: Fri Feb 27, 2004 9:54 pm

RE: Fly-by-wire... Blessing Or A Curse?

Thu Dec 30, 2004 5:03 am

Much has been made and discussed about the Captain's statements after the incident, including some talk about missing FDR recordings. Not quite such a field day for conspiracy theorists as TWA800, but still.

My belief is that aircraft cannot fly outside the laws of physics. The plane was slowing down and descending at a very low altitude. 100 or 30 feet doesn't really make that much difference in this case given treetop height. And the fact that it was an Airbus lulled the crew into a false sense of security. Envelope protection or not, what they tried was not very bright.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
delta-flyer
Posts: 2631
Joined: Mon Jul 30, 2001 9:47 am

RE: Fly-by-wire... Blessing Or A Curse?

Thu Dec 30, 2004 6:56 am

Regardless of the precise technical factors, the FBW scheme was fairly new to pilots, and probably they did not have sufficient practice in such conditions, that represent the extremes of the operating envelope.

Despite statements to the contrary, my friend at Airbus confirms that many software improvements were made as a result of this accident, and others that followed. That's just a natural evolution - we always learn from accidents and always make things better.

Back to the original question - is FBW a positive advance? I say unequivocally! Adding the computer between the pilot and flight control system provides tremendous possibilities, whose surface we are just barely scratching.

Cheers,
Pete
"In God we trust, everyone else bring data"

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos