Airbus ALTN LAW - FOR LDG USE FLAP 3

[bulfly]

A silly question for the A_Bus drivers!

Has anyone seen an Airbus written reference as to why when in ALTN LAW FOR LDG one has to USE FLAP 3 ?

I presume that the answer is in the fact that "...maneuver protections (pitch, bank) are lost..." (notes to same procedure), but I was unable to find any pertinent written reference!

I thank you!

[J.O.]

I don't have a written reference for it, but Flap 3 is used for landing with any abnormal operation which results in alternate law. I believe it is because Flap 3 provides for slightly better aircraft handling, particularly if there is turbulence or wind shear.

[Dream Land]

Flaps 3 is the configuration for Direct Law, when operating in Alternate law you will end up in Direct Law when landing gear goes down.

[Major Cleve Saville]

Furthermore FLight Control Laws are dependent on Flap Lever position. If you select anything other than Flap Lever position 3 for Alternate Law/Direct Law landing landing i.e. Flap Lever position Full the Flight Control laws will be incorrect for Alternate Law / Direct Law. The aircraft is difficult to control. I believe some people have nearly come adrift because of this.

[Don Coyote]

"Flight control laws are dependant on flap lever position" :bored: Never heard that before.

[bobrun]

when operating in Alternate law you will end up in Direct Law when landing gear goes down
I believe that the transition to Direct Law (should say Flare law really) with gear down selection happens with dual RA failed if autopilot is off, not when in alternate law.

[fmgc]

Guys, you are assuming that we are talking about 320 or 330, but they are different and the original question was about Airbuses.

Bobrun, on a 320 if you are in Alt law then you will go into Direct Law on gear down, always. You will go into direct law with a double rad alt failure on gear down too, direct from normal law.

Dreamland, that is not the case on the 330, you will stay in Alt Law in a lot of instances.

[Dream Land]

Yes I operate the small bus. :ouch:

[idg]

As I understand it MCS is correct when he talks of control 'law' switching with flap lever position.

We are NOT talking about Normal or Alternate Law but the response rate of the controls with relation to sidestick deflection. F3 will give more roll response (ie bigger rate) with the same sidestick input than will Ffull. This came to light after an incident on one of our minibusses many years ago.

The slats were not in the correct position and the flap handle was put to the full position. This resulted in an a/c very difficult to handle because the roll response was incorrectly scheduled.

Normally this rate change is transparent to the pilot and thus is not dicussed in the FCOMs. It is VERY important to use the correct Flap Handle position when there is any Flap or slay fault present.

A double rad alt failure will cause Alternate law then Direct law because the a/c cannot 'schedule' the change over to flare law as it nears the ground cos it doesn't know when it's approaching terra firma. It therefore leaves it up to the pilot!

B'run
Technically correct, but with the a'pilot off then Direct law will kick in with gear down. Better though to wait for F3 and Gear down cos then you wont have to trim it with the wheel!

[FlapsOne]

Bobrun

I'd have another read about Flare Law if I were you.

[Clandestino]

We are NOT talking about Normal or Alternate Law but the response rate of the controls with relation to sidestick deflection. F3 will give more roll response (ie bigger rate) with the same sidestick input than will Ffull. This came to light after an incident on one of our minibusses many years ago.

Erm... methinks that alternate/direct refers only to pitch law. If you get alternate law in pitch, your roll goes into direct, so no more roll rate demand and aileron deflection is (gaaaasp) directly proportional to sidestick deflection. So if you´re in altn/dir law no change to roll response when you switch configs. Well, on A320 anyway.

It seems there´s not much difference between config 3 and full on landing. But that is in sim. I still have zero hours on the real thing.

[Dream Land]

Small point, but a dual RA fault goes from Normal law straight to Direct law when gear selected (pretty sure at least:confused: ).

[CapedCrewsAider]

Only Major Cleve Saville and idg seem to know their stuff here. The 'fine tuning' of the Flight Control Laws, in this case (alternate law) the amount of aileron deflection commanded by a given sidestick deflection is determined by Flap Lever position (note: not the actual slat/flap config.)
I am somewhat astounded to see someone like clandestino who has not flown the aircraft have the confidence to a somewhat derisve post based on a few hours in a sim.
Clandestiono: the sidestick is not directly connected by cables to the ailerons, so has it not occurred to you that the ELACS still control the ailerons and you may not have full knowledge of how the ELACS have been programmed or how the stick deflection/aileron displacement ratio is altered by Flap Lever position.
Don Coyote: just because you have never heard it does not make it false. Looks like a case of don't confuse me with facts my mind is made up. I suggest you google: Dragonair A320 Incident Hong Kong 1994.
I have seen crews, in the sim, inadvertently select Flaps Full whilst attempting an Alternate-Direct law landing and can confirm that controlability is 'somewhat' impaired.
Why do we select Flaps 3 for abnormal configs (except flaps/slats 0) on the A320 - because Airbus tell us to and they have more knowledge of the way the A320 works than we do.
During dual rad alt failure the Flight Control Laws go directly to Direct Law at gear down because a radio altimeter input is required to programme flare law.
i.e Flare law is not available without rad alts.
'A little knowledge is a dangerous thing'. 'How does that system work? It works really well'.

[bobrun]

FlapsOne,
We must be talking about different types, as my book confirms what I said.
Dreamland,
Again, I'm not on the 320 and didn't realize some of the differences between types. On my type, what you say regarding a dual RA failure is true assuming the AP is off.

[Tree]

idg:

Config Full activates roll spoilers and ailerons immediately with any lateral movement of the sidestick. Config 3 activates ailerons first then roll spoilers beyond a certain lateral threshold movement of the sidestick. Config Full is prone to overcontrol and PIO. Config 3 is therefore recommended for gusty crosswind and icing conditions.
There is a factory FOT with the details.

[FlapsOne]

Dream Land is correct - Bobrun you have your wires crossed.

A dual RA fault will get you from Normal Law to Direct Law with the gear down because, wihtout RA, there can be no Flare Law.

Dct Law with the gear down following certain failures has absloutely nothing whatsoever to do with flare law.

Flare law is the thing that gets you from Normal law Flight Mode to Normal law Ground mode and allows you to land the airbus with conventional 'feel'.

[Right Way Up]

There is a lot of strong discussion about this subject, but unfortunately between pilots who are on quite different variants of the airbus fleet. Can I suggest when quoting FCOMs that you state the airbus type to stop confusion. To put my two pennyworth in I would have thought having flap 3 for approach (A319) when ALTN Law will change to DCT Law will make the go-around slightly easier. With only manual pitch trim the change from flap 3 to flap 2 should be easier than flap full to flap 3.

[Wingswinger]

Just to be pedantic - on minibuses it's Flare Mode of Normal Law and Flare Mode of Alternate Law which happens to be Pitch Direct/Roll Direct.

[hetfield]

My airbus neither has Alternate law nor Flap3:)

[FlapsOne]

Correct wingswinger.

Indeed the 'Flare mode' of Alt law isn't really a flare mode at all. It just gives Dct Law because it is unable to give a proper flare made at landing and AI never wanted anyone to land the thing in 'normal law'.

[Right Way Up]

Can someone give me a reference to "flare mode" of altn law? I have never seen this teminology used on the minibus. My understanding is that with gear down in altn law the logic changes to good old "direct law". (Unless you have had an abnormal attitude but that would be another thread):zzz: :zzz:

[Wingswinger]

FCOM 1.27.30. Alternate Law. Diagram on pitch control.

[Right Way Up]

Thanks for the reference wingswinger. Thats probably why I dislike the FCOM on computer, very easy to miss some of these diagrams.

[Clandestino]

Clandestiono: the sidestick is not directly connected by cables to the ailerons, so has it not occurred to you that the ELACS still control the ailerons and you may not have full knowledge of how the ELACS have been programmed or how the stick deflection/aileron displacement ratio is altered by Flap Lever position.


:O Indeed I´ve posted it wrongly: in direct law there´s switch in ELAC bias as slats extend from zero, but that´s as much as my FCOM would let me know. Did you get your data from maintenance manual?

[FlightDetent]

Older thread here (http://www.pprune.org/forums/showthread.php?t=245735&page=2&highlight=direct+alternate+law).

FD
(the un-real)

[bobrun]

FlapsOne,
If you are correct, then my manual will have to be amended......here's the quote (straight from the book) regarding a dual RA failure (A330/A340):

(...) mode switching is as follows:
· At take-off, normal law becomes active when the MLG is no longer
compressed and pitch attitude becomes greater than 8°.
· On approach, the flare law becomes active in manual flight when the L/G is extended. If the AP is engaged when the L/G is extended, flare law becomes active at AP disconnect. As and when flare law activates, manual pitch trim is required and “USE MAN PITCH TRIM” is displayed on the PFD.
(...)
:hmm:

[FlapsOne]

Maybe it's different for the 320 series 'cos I cannot find that.

As I have always understood it (since TLS) is that, without RA data, the system cannot give flare mode (the trim adjustment to give flare 'feel') and thus the only course of action is to give DCT LAW (where we all learnt to fly!).