Airbus Flight control laws
Airbus say :
weight saving is considerable, the system is cheaper, safer (!) and allows the handling characteristics of all types (A319-A340/A380) to be closely matched to allow common type ratings and MFF.
weight saving is considerable, the system is cheaper, safer (!) and allows the handling characteristics of all types (A319-A340/A380) to be closely matched to allow common type ratings and MFF.
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Not aware of 'Take off law' or 'Landing law' - not in any Airbus documents I have.
There is NORMAL LAW - which has Ground mode, Flight mode and Flare mode; ALTERNATE LAW - which is a slightly degraded form of normal law offering certain reduced protections and DIRECT LAW - which is the same law 'used' by everything at your local flying club.
Don't know why Airbus chose this route but it's nowhere near as complicated as certain explanations try to make it sound. Having said that, it's harder to write down (type) than to explain verbally or actually operate. It takes approx 10 mins to get used to and 15 mins to totally enjoy.
Bottom line, the aircraft fly very well indeed and have to suffer several (big) failures before they end up in DIRECT LAW - which is where we all all learnt to fly!
There is NORMAL LAW - which has Ground mode, Flight mode and Flare mode; ALTERNATE LAW - which is a slightly degraded form of normal law offering certain reduced protections and DIRECT LAW - which is the same law 'used' by everything at your local flying club.
Don't know why Airbus chose this route but it's nowhere near as complicated as certain explanations try to make it sound. Having said that, it's harder to write down (type) than to explain verbally or actually operate. It takes approx 10 mins to get used to and 15 mins to totally enjoy.
Bottom line, the aircraft fly very well indeed and have to suffer several (big) failures before they end up in DIRECT LAW - which is where we all all learnt to fly!
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I understand that FBW is lighter, cheaper to maintain, "safer" etc. buut why this method of controlling. As I said, the 777 is FBW but totally conventionally controlled. What drove Airbus down the path they went on? I suppose the commonality point is a good one, but couldn't you engineer any FBW system to give pre-programmed feedback to the pilot?
Flapsone - Good point, I suppose most things in flying are a heck of a lot easier to do than to describe!
Flapsone - Good point, I suppose most things in flying are a heck of a lot easier to do than to describe!
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Not aware of 'Take off law' or 'Landing law' - not in any Airbus documents I have.
There is NORMAL LAW - which has Ground mode, Flight mode and Flare mode; ALTERNATE LAW - which is a slightly degraded form of normal law offering certain reduced protections and DIRECT LAW - which is the same law 'used' by everything at your local flying club.
Don't know why Airbus chose this route but it's nowhere near as complicated as certain explanations try to make it sound. Having said that, it's harder to write down (type) than to explain verbally or actually operate. It takes approx 10 mins to get used to and 15 mins to totally enjoy.
Bottom line, the aircraft fly very well indeed and have to suffer several (big) failures before they end up in DIRECT LAW - which is where we all all learnt to fly!
There is NORMAL LAW - which has Ground mode, Flight mode and Flare mode; ALTERNATE LAW - which is a slightly degraded form of normal law offering certain reduced protections and DIRECT LAW - which is the same law 'used' by everything at your local flying club.
Don't know why Airbus chose this route but it's nowhere near as complicated as certain explanations try to make it sound. Having said that, it's harder to write down (type) than to explain verbally or actually operate. It takes approx 10 mins to get used to and 15 mins to totally enjoy.
Bottom line, the aircraft fly very well indeed and have to suffer several (big) failures before they end up in DIRECT LAW - which is where we all all learnt to fly!
Only half a speed-brake
This must be the thread with most correct answers ever. 
Apart from the "normal law" the FBW provides for some "reconfiguration laws". These are:
All are correctly described in the post above. Perhaps except for the mechanical back-up that enables the pilot to control the aircraft during temporary complete loss of electrical power. Pitch is controlled manually by setting the trimmable horizontal stabiliser and lateral control is provided conventionally via rudder and pedals. Airbus claims that aircraft were succesfully landed in mech. backup, however such manuoevre is not part of the training curriculum.
FD
(the un-real)
Apart from the "normal law" the FBW provides for some "reconfiguration laws". These are:
- Alternate law (with reduced protections)
- Alternate law (w/o reduced protections)
- Direct Law
- Mechanical back-up
All are correctly described in the post above. Perhaps except for the mechanical back-up that enables the pilot to control the aircraft during temporary complete loss of electrical power. Pitch is controlled manually by setting the trimmable horizontal stabiliser and lateral control is provided conventionally via rudder and pedals. Airbus claims that aircraft were succesfully landed in mech. backup, however such manuoevre is not part of the training curriculum.
FD
(the un-real)
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MECH BACKUP i.e. only ths and rudder is encountered only at ridculously high level of multiple failure eg : all comp failure-
SEC 1+2+3+ELAC1+2+FAC1+2 phew!!.
once in a while we try it on the sims freeplay.( sim is set up calm cavok ). fool around on the down wind to come to grips with the trim (tremendous amount of control lag) use rudder sparingly, wait for the secondary effect of yaw
well after a while 
we actually landed it
SEC 1+2+3+ELAC1+2+FAC1+2 phew!!.
once in a while we try it on the sims freeplay.( sim is set up calm cavok ). fool around on the down wind to come to grips with the trim (tremendous amount of control lag) use rudder sparingly, wait for the secondary effect of yaw well after a while we actually landed it
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Just to ad up another law no one talked about: ABNORMAL law!
Let's say we are flying into extreme weather, aircraft flips over due to very strong turbulences, it will leave the protected envellop, normal laws will be exceeded and abnormal law becomes active.
This is a safety feature to ensure that the flight control computers will never prevent the pilots from recovering from abnormal attitude.
I may be wrong: got my type rating last december , sent 50 resumes, was invited to one single interview...and still on the ground...
Let's say we are flying into extreme weather, aircraft flips over due to very strong turbulences, it will leave the protected envellop, normal laws will be exceeded and abnormal law becomes active.
This is a safety feature to ensure that the flight control computers will never prevent the pilots from recovering from abnormal attitude.
I may be wrong: got my type rating last december , sent 50 resumes, was invited to one single interview...and still on the ground...
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So much for user-friendly
i fly the 330. that what i get paid to do. given the choice, Boeing ANYTIME.
anybody remember KISS ? just look at the disaster airbus has gone and done on the 380. some
guys sound like nerd geeks, not pilots.
anybody remember KISS ? just look at the disaster airbus has gone and done on the 380. some
guys sound like nerd geeks, not pilots.
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Well,
He gets off the wheel and puts his little parachute on and.....
Just kidding. it deploys automaticly in an serious electrical failure or is deployed manually for a hydraulic failure or various combinations thereof.
Depending on which failure the sim guy is throwing at you. You'll follow the ECAM procedure and ftfp. Okay? Have at it techno geeks!
RDG
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I must add respect to the test pilot who managed to land the thing in mechanical back up! Tried it in the sim when I was doing my initial A330 endorsement and the results were "none to pleasing"......................and that is being generous from the sim instructor!
Go Airbus!!!!!
Go Airbus!!!!!
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I wonder if the PF ( RIP ) on AA 587 an Airbus A300-600 (A NON FBW airbus from1984 re-design of earlier A300 ) which crashed at Belle Harbour in 2001 wished he had FBW protection against his excessive aggressive rudder movement which snapped off the Vert Stab according to NTSB?
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I wonder if the PF ( RIP ) on AA 587 an Airbus A300-600 (A NON FBW airbus from1984 re-design of earlier A300 ) which crashed at Belle Harbour in 2001 wished he had FBW protection against his excessive aggressive rudder movement which snapped off the Vert Stab according to NTSB?
Anyone?
palgia
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I found this on www.airbusdrivers.net, I am not claiming that I wrote it, and the name of the author is not published on the website.
Normal operating configuration of the system. Failure of any single computer does not affect normal law.
Covers 3-axis control, flight envelope protection, and load alleviation. Has 3 modes according to phase of flight.
Ground Mode
• Active when aircraft is on the ground.
• Direct proportional relationship between the sidestick deflection and deflection of the flight controls.
• Is active until shortly after liftoff.
• After touchdown, ground mode is reactivated and resets the stabilizer trim to zero.
Flight Mode
• Becomes active shortly after takeoff and remains active until shortly before touchdown.
• Sidestick deflection and load factor imposed on the aircraft are directly proportional, regardless of airspeed.
• With sidestick neutral and wings level, system maintains a 1 g load in pitch.
• No requirement to change pitch trim for changes in airspeed, configuration, or bank up to 33 degrees.
• At full aft/fwd sidestick deflection system maintains maximum load factor for flap position.
• Sidestick roll input commands a roll rate request.
• Roll rate is independent of airspeed.
• A given sidestick deflection always results in the same roll rate response.
• Turn coordination and yaw damping are computed by the ELACs and transmitted to the FACs.
• No rudder pedal feedback for the yaw damping and turn coordination functions.
Flare Mode
• Transition to flare mode occurs at 50' RA during landing.
• System memorizes pitch attitude at 50' and begins to progressively reduce pitch, forcing pilot to flare the aircraft
• In the event of a go-around, transition to flight mode occurs again at 50' RA.
Protections Load factor Limitation
• Prevents pilot from overstressing the aircraft even if full sidestick deflections are applied.
Attitude Protection
• Pitch limited to 30 deg up, 15 deg down, and 67 deg of bank.
• These limits are indicated by green = signs on the PFD.
• Bank angles in excess of 33 deg require constant sidestick input.
• If input is released the aircraft returns to and maintains 33 deg of bank.
High Angle of Attack Protection (alpha):
• When alpha exceeds alpha prot, elevator control switches to alpha protection mode in which angle of attack is proportional to sidestick deflection.
• Alpha max will not be exceeded even if the pilot applies full aft deflection
High Speed Protection:
• Prevents exceeding VMO or MMO by introducing a
pitch up load factor demand.
• The pilot can NOT override the pitch up command.
Low Energy Warning:
• Available in CONF 2,3, or FULL between 100' and 2,000' RA when TOGA not selected.
• Produces aural "SPEED SPEED SPEED" when change in flight path alone is insufficient to regain a positive flight path (Thrust must be increased).
ALTERNATE LAW
If Multiple Failures of Redundant Systems occur, the flight controls revert to Alternate Law.
The ECAM displays the message: ALTN LAW: PROT LOST
Ground
Mode The ground mode is identical to Normal Law.
Flight Mode
• In pitch alternate law the flight mode is a load factor demand law similar to the Normal Law flight mode, with reduced protections.
• Pitch alternate law degrades to pitch direct law when the landing gear is extended to provide feel for flare and landing, since there is no flare mode when pitch normal law is lost.
• Automatic pitch trim and yaw damping (with limited authority) is available.
• Turn coordination is lost.
• When pitch law degrades from normal law, roll degrades to Direct Law - roll rate depends on airspeed.
Protections
• All protections except for load factor maneuvering protection are lost.
• The load factor limitation is similar to to that under Normal Law.
• Amber XX's replace the green = attitude limits on the PFD.
• A low speed stability function replaces the normal angle-of-attack protection
o System introduces a progressive nose down command which attempts to prevent the speed from decaying further.
o This command CAN be overridden by sidestick input.
o The airplane CAN be stalled in Alternate Law.
o An audio stall warning consisting of "crickets" and a "STALL" aural message is activated.
o The Alpha Floor function is inoperative.
• The PFD airspeed scale is modified:
o VLS remains displayed
o VALPHA PROT and VALPHA MAX are removed
o They are replaced by a red and black barber pole, the top indicating the stall warning speed VSW
• A nose up command is introduced any time the airplane exceeds VMO/MMO to keep the speed from increasing further, which CAN be overridden by the sidestick.
• Bank angle protection is lost.
• Certain failures cause the system to revert to Alternate Law without speed stability.
• Yaw damping is lost if the fault is a triple ADR failure.
ABNORMAL ALTERNATE LAW
Abnormal Alternate Law is activated if the airplane enters an unusual attitude, allowing recovery from the unusual attitude.
• Pitch law becomes Alternate (without autotrim or protection other than Load Factor protection).
• Roll law becomes Direct law with mechanical yaw control.
• After recovery from the unusual attitude, the following laws are active for the remainder of the flight:
o Pitch: Alternate law without protections and with autotrim.
o Roll: Direct law
o Yaw: Alternate law
• There is no reversion to Direct law when the landing gear is extended.
DIRECT LAW
Direct law is the lowest level of computer flight control and occurs with certain multiple failures.
• Pilot control inputs are transmitted unmodified to the control surfaces, providing a direct relationship between sidestick and control surface.
• Control sensitivity depends on airspeed and NO autotrimming is available.
• An amber message USE MAN PITCH TRIM appears on the PFD.
• If the flight controls degrade to Alternate Law, Direct Law automatically becomes active when the landing gear is extended if no autopilots are engaged. If an autopilot is engaged, the airplane will remain in Alternate Law until the autopilot is disconnected.
• There are no protections provided in Direct Law, however overspeed and stall aural warnings are provided.
• The PFD airspeed scale remains the same as in Alternate Law.
MECHANICAL BACKUP
In case of a complete loss of electrical flight control signals, the aircraft can be temporarily controlled by mechanical mode.
• Pitch control is achieved through the horizontal stabilizer by using the manual trim wheel.
• Lateral control is accomplished using the rudder pedals.
• Both controls require hydraulic power.
• A red MAN PITCH TRIM ONLY warning appears on the PFD.
AIRBUS FLIGHT CONTROL LAWS
NORMAL LAWNormal operating configuration of the system. Failure of any single computer does not affect normal law.
Covers 3-axis control, flight envelope protection, and load alleviation. Has 3 modes according to phase of flight.
Ground Mode
• Active when aircraft is on the ground.
• Direct proportional relationship between the sidestick deflection and deflection of the flight controls.
• Is active until shortly after liftoff.
• After touchdown, ground mode is reactivated and resets the stabilizer trim to zero.
Flight Mode
• Becomes active shortly after takeoff and remains active until shortly before touchdown.
• Sidestick deflection and load factor imposed on the aircraft are directly proportional, regardless of airspeed.
• With sidestick neutral and wings level, system maintains a 1 g load in pitch.
• No requirement to change pitch trim for changes in airspeed, configuration, or bank up to 33 degrees.
• At full aft/fwd sidestick deflection system maintains maximum load factor for flap position.
• Sidestick roll input commands a roll rate request.
• Roll rate is independent of airspeed.
• A given sidestick deflection always results in the same roll rate response.
• Turn coordination and yaw damping are computed by the ELACs and transmitted to the FACs.
• No rudder pedal feedback for the yaw damping and turn coordination functions.
Flare Mode
• Transition to flare mode occurs at 50' RA during landing.
• System memorizes pitch attitude at 50' and begins to progressively reduce pitch, forcing pilot to flare the aircraft
• In the event of a go-around, transition to flight mode occurs again at 50' RA.
Protections Load factor Limitation
• Prevents pilot from overstressing the aircraft even if full sidestick deflections are applied.
Attitude Protection
• Pitch limited to 30 deg up, 15 deg down, and 67 deg of bank.
• These limits are indicated by green = signs on the PFD.
• Bank angles in excess of 33 deg require constant sidestick input.
• If input is released the aircraft returns to and maintains 33 deg of bank.
High Angle of Attack Protection (alpha):
• When alpha exceeds alpha prot, elevator control switches to alpha protection mode in which angle of attack is proportional to sidestick deflection.
• Alpha max will not be exceeded even if the pilot applies full aft deflection
High Speed Protection:
• Prevents exceeding VMO or MMO by introducing a
pitch up load factor demand.
• The pilot can NOT override the pitch up command.
Low Energy Warning:
• Available in CONF 2,3, or FULL between 100' and 2,000' RA when TOGA not selected.
• Produces aural "SPEED SPEED SPEED" when change in flight path alone is insufficient to regain a positive flight path (Thrust must be increased).
ALTERNATE LAW
If Multiple Failures of Redundant Systems occur, the flight controls revert to Alternate Law.
The ECAM displays the message: ALTN LAW: PROT LOST
Ground
Mode The ground mode is identical to Normal Law.
Flight Mode
• In pitch alternate law the flight mode is a load factor demand law similar to the Normal Law flight mode, with reduced protections.
• Pitch alternate law degrades to pitch direct law when the landing gear is extended to provide feel for flare and landing, since there is no flare mode when pitch normal law is lost.
• Automatic pitch trim and yaw damping (with limited authority) is available.
• Turn coordination is lost.
• When pitch law degrades from normal law, roll degrades to Direct Law - roll rate depends on airspeed.
Protections
• All protections except for load factor maneuvering protection are lost.
• The load factor limitation is similar to to that under Normal Law.
• Amber XX's replace the green = attitude limits on the PFD.
• A low speed stability function replaces the normal angle-of-attack protection
o System introduces a progressive nose down command which attempts to prevent the speed from decaying further.
o This command CAN be overridden by sidestick input.
o The airplane CAN be stalled in Alternate Law.
o An audio stall warning consisting of "crickets" and a "STALL" aural message is activated.
o The Alpha Floor function is inoperative.
• The PFD airspeed scale is modified:
o VLS remains displayed
o VALPHA PROT and VALPHA MAX are removed
o They are replaced by a red and black barber pole, the top indicating the stall warning speed VSW
• A nose up command is introduced any time the airplane exceeds VMO/MMO to keep the speed from increasing further, which CAN be overridden by the sidestick.
• Bank angle protection is lost.
• Certain failures cause the system to revert to Alternate Law without speed stability.
• Yaw damping is lost if the fault is a triple ADR failure.
ABNORMAL ALTERNATE LAW
Abnormal Alternate Law is activated if the airplane enters an unusual attitude, allowing recovery from the unusual attitude.
• Pitch law becomes Alternate (without autotrim or protection other than Load Factor protection).
• Roll law becomes Direct law with mechanical yaw control.
• After recovery from the unusual attitude, the following laws are active for the remainder of the flight:
o Pitch: Alternate law without protections and with autotrim.
o Roll: Direct law
o Yaw: Alternate law
• There is no reversion to Direct law when the landing gear is extended.
DIRECT LAW
Direct law is the lowest level of computer flight control and occurs with certain multiple failures.
• Pilot control inputs are transmitted unmodified to the control surfaces, providing a direct relationship between sidestick and control surface.
• Control sensitivity depends on airspeed and NO autotrimming is available.
• An amber message USE MAN PITCH TRIM appears on the PFD.
• If the flight controls degrade to Alternate Law, Direct Law automatically becomes active when the landing gear is extended if no autopilots are engaged. If an autopilot is engaged, the airplane will remain in Alternate Law until the autopilot is disconnected.
• There are no protections provided in Direct Law, however overspeed and stall aural warnings are provided.
• The PFD airspeed scale remains the same as in Alternate Law.
MECHANICAL BACKUP
In case of a complete loss of electrical flight control signals, the aircraft can be temporarily controlled by mechanical mode.
• Pitch control is achieved through the horizontal stabilizer by using the manual trim wheel.
• Lateral control is accomplished using the rudder pedals.
• Both controls require hydraulic power.
• A red MAN PITCH TRIM ONLY warning appears on the PFD.
