whats the main difference btwn airbus FBW and the 777 FBW

[matamisa]

anyone?
cheers

[XPMorten]

The short version,

"In Airbus aircraft, the computer always retains ultimate control and will not permit the pilot to fly outside the airplane's normal flight envelope. In a Boeing 777, the pilot can override the system, allowing the plane to be flown outside this envelope in emergencies."

This is not really true either since the Airbus pilot can override the computer
by switching off the augmentation computers and IRS's.

Cheers,

M

[Old Smokey]

XPMorten covered it nicely. Another significant difference is that the B777 has a real wire (a steel one) connected to pitch and roll control as a last ditch means of control if all else fails. That's my kind of fly by wire

Regards,

Old Smokey

[matamisa]

Originally Posted by Old Smokey

XPMorten covered it nicely. Another significant difference is that the B777 has a real wire (a steel one) connected to pitch and roll control as a last ditch means of control if all else fails. That's my kind of fly by wire
Regards,
Old Smokey

what about the airbus backup

[Shaka Zulu]

True as that may be Old Smokey the signal from the Yoke to the ACE's is still an electric one, even in Direct Mode.... (same goes for the alternate pitch trim).

At least that's how I read the system...

[FE Hoppy]

Airbus/Boeing??
Embraer:- Similar to 777

Direct Mode:- sensors(LVDT/RVDT) mounted on the control column send analogue electrical signals to the Actuator Control Electronic (ACE) this is an analogue circuit that controls the position of the PCU/control surface. all analogue, no software input.

Normal Mode:- As above but the ACE also receives input from the Flight Control Module(FCM) which it sums with the pilot input to give high level augmentation such as Airspeed gain schedule, mach trim(190) AoA limiting, Configuration trim, Elevator thrust compensation, Yaw damping and turn co-ordination and one day maybe thrust assimetry compensation.

same company makes the embraer and boeing systems.

[Check Airman]

Assuming we're staying in normal law, and not pulling any breakers:

Airbus computers limit the pilot's commands and have final authority.

Boeing computers TRY to limit the pilot's input, but can be overridden by applying excess force. This force is way beyond the normal forces required, so the pilot cannot inadvertently exceed limits. It must be a deliberate effort, possibly requiring both crewmembers.

IMHO the boeing system is safer overall. Look at this article. I'm not so sure the outcome would be as good on an airbus.

[Hand Solo]

I'm not so sure the outcome would be as good on an airbus

Its never happened on an Airbus, despite it being a much older FBW system with many more sectors accumulated over its life span than the 777. Perhaps Boeing need to take some lessons in how to design redundancy and automatic integrity monitoring into a FBW system.

[Check Airman]

Originally Posted by Hand Solo

Its never happened on an Airbus, despite it being a much older FBW system with many more sectors accumulated over its life span than the 777. Perhaps Boeing need to take some lessons in how to design redundancy and automatic integrity monitoring into a FBW system.

I see ur point that airbus has logged far more FBW hrs than boeing, but assuming it has indeed never happened. the boeing pilot would still be safer. We can't put too much faith in system redundancy, because enen the standby backups will fail.

[Old Smokey]

Originally Posted by Shaka Zulu

True as that may be Old Smokey the signal from the Yoke to the ACE's is still an electric one, even in Direct Mode.... (same goes for the alternate pitch trim).
At least that's how I read the system...

What you say, Shaka Zulu, is absolutely correct for the Direct Mode, but if you refer to the Boeing Vol 2 immediately following the description of Direct Mode, you will see....

Mechanical Backup

In the unlikely event of a complete electrical system shut-down, cables from the flight deck to the stabilizer and selected spoilers allow the pilot to fly straight and level until the electrical system is restarted. (End of quote).

No electrics required, just a good old steel cable to the hydraulic actuator/s. Hydraulics are, of course necessary.

Perhaps Shaka, we were reading from a different version of the Boeing manual (Prooners, that's not sarcasm, it's a private joke).

Does Airbus have a last ditch mechanical backup such as this? I don't know, it's an honest question.

Regards,

Old Smokey

[Hand Solo]

On the 320 the rudder and stabiliser have mechanical backup. Not easy to fly with it though!

[Shaka Zulu]

Originally Posted by Old Smokey

In the unlikely event of a complete electrical system shut-down, cables from the flight deck to the stabilizer and selected spoilers allow the pilot to fly straight and level until the electrical system is restarted. (End of quote).
No electrics required, just a good old steel cable to the hydraulic actuator/s. Hydraulics are, of course necessary.
Perhaps Shaka, we were reading from a different version of the Boeing manual (Prooners, that's not sarcasm, it's a private joke).
Does Airbus have a last ditch mechanical backup such as this? I don't know, it's an honest question.
Regards,
Old Smokey

Hmmm yes indeed it's a cable going to the Stab however the signal from the Yoke to the ACE's (where the cable is attached to so to speak) is still an analogue eletrical one. But now we are nitpicking

And no I think both of our Ops Manuals agree on that one, and thanks again, it has helped me getting through the course!

[gengis]

Also the 777 FBW is "speed" stable - in other words it maintains an in-trimmed speed. Whereas the Airbus FBW (i am given to understand) is "attitude" stable; it maintains the attitude at which the joystick was released.

There's a big difference in this.

[Bolty McBolt]

airbus 330/340 back up comes thru basic redundancy in the form of 5 flight control computers.3 priamary 2 secondary. All are capable of controling the plane but in a reduced capacity.
If a computer in charge fails next takes over with the loss of some surfaces eg Spoiler with no loss of aircraft stability/control.

Direct cable cable input to the stab trim and early models have direct cable input to rudder pca s.
Late model have a tiny back up control module in the form of a tiny hydraulic powered generator which supplys power to a backup RVDT on rudder pedals and power to the servovalve on the rudder PCP.

I like the boeing system better

[Jet II]

Originally Posted by Bolty McBolt

airbus 330/340 back up comes thru basic redundancy in the form of 5 flight control computers.3 priamary 2 secondary. All are capable of controling the plane but in a reduced capacity.

777 has 3 FCC's but each have 3 lanes - therefore total of 9 independant computers each capable of controlling aircraft on its own.

And I like the Boeing system better as well