G + B Hydraulic Failure A320
 

In G + B Hydraulic failure in A320 it is not required to extend L/G at 200kts if Slats are extended. Can someone please explain why so when slats are extended. Thanks.

As I understand it, it relates to optimum pitch control which is better in Direct rather Alternate Law, under certain circumstances.

If you do not have slats extended (G+B lost) and have lost 1 elevator (left G lost) the book get you to select L/G down forcing you into Direct Law where the pitch control is better than in Alternate Law without Slats.

FCOM PRO-ABN-29

Extend the landing gear at 200 kt to revert sooner in direct law. This provides, below 200 kt , a better pitch control than in alternate law with one elevator lost and all slats lost.

I assume that pitch control with Slats extended is better than without Slats at 200kts so no need to force the aircraft into Direct Law yet.

Sorry but where is written that when slats are extended you dont have to extend the gear at 200 knots?

Am I missing something here?

I can only refer to QRH dual Hyd!

FCOM is clear,

If slats are extended, the L/G grav ext will not appear, so there is no reason to extend it.

So you can but not required.

FCOM PRO-ABN-29: Q
Attachment 1357

Who can explain why if slats are at 1, then ECAM says that approach speed is Vref + 10 and not + 25, but it does not mention this in the FCOM?

Because to determine the inflight landing distance, you have to use the matrix with the longest ref distance.
In this case is Direct law and dictates deltaVref is +10.

Although there is no direct answer I will try to explain it using available info and logic. With G+B fail you loose left elevator and slats. With only half elevator to create the required aerodynamic force it has to move double the amount it would move with both sides working. Besides being on one side of longitudinal axis it causes rotary motion like an aileron which needs to be resisted causing torsion on the fuselage. So elevator handling needs to be gentle and only to the required amount. In normal/alternate law fore and aft side stick movement is linear load factor demand which flight control computer gives by moving the elevator. So there is a possibility of elevator hitting the stops causing damage so the aircraft automatically restricts the maximum movement. At high speed because of V square it is not a problem but at lower speed a certain G demand may move the elevators to extremes. This also aggravates torsion. This can be prevented by inducing direct law and moving the stick/elevator to required amount and also being gentle. Harsh stick inputs cause false stall warnings which pilot doesn't know as false. Therefore first gear down at two hundred kts. Now why not with slats? Because to get slats you would be in normal law may be with single hydraulic failure and your speed would be closer towards S which is correct speed till now. So if double failure occurs now you are already there and can continue to flap2 and gear down(gravity extension) and flap3.

Holymoley
With slats 1 you only missing one step of slats as flaps are available. So why would it be Vref+25. FCOM directs you to slat/flam jam procedure which will give the delta Vref.

You have to ask yourself why is direct law required at 200 kts only when slats are retracted.
My ancient FCOM circa 2000 "G+B SYS LO PR Summary" recommended only lowering the gear when in Landing CONF and at VAPP even when the slats were retracted.

The significant change since 2003 was the introduction of A318 with a 6m shorter fuselage - hence shorter moment arm at the tail.

Probably the most difficult part of performing the G+B procedure is handling the aircraft whilst running the flaps from zero to F2 in one move at just below the F2 speed limit of 200 kts but above the "Stall Stall" warning. It is easy to trigger a momentary stall warning in the simulator by pulling some delta g as the flaps run out. In real life you would "feel" this delta g and respond instinctively by lowering the nose. There is no delta g sensation in the simulator so the pilot often lags behind the simulator and can unintentionally activate the stall warning.

Better pitch control is achieved in direct law with manual thrust and manual pitch trim - ask any Boeing pilot.

Didn't check the FCOM because in these failures usually I refer directly to the QRH, thanks by the way I wasn't aware of this.

I believe because slats when extended move the center of pressure forward, there is less effort of the remaining elevator.

Golden
Are you sure you are not talking about G+Y where you configure to landing conf? Even 2001 Instructor Support says following:
In the event of loss of G + B, the speed has to be increased to 200 kt during gravity extension to provide a good pitch control until stabilized.
The flight controls revert to direct law.
You cannot do this in conf3.

villas,
I'm very confident it was for G+B HYD Loss.
G+B.pdf

That's not what's on your picture. Irrelevant to the discussion about 200 kt L/G down, I know.

For standardization you fly 200 gear down. That's what I learned today!

When document clearly states to provide good pitch control it is not definitely not for standardisation. And it is there at least from year 2001. Standardise with what? The standard way of configuration is 1+2 GD and 3. There are only two exceptions G+Y fail where it is 1+2+3 then at Vapp GD and G+B where it is 200kts GD then 1+2+3.

They dont separate the case of slats extended or slats not extended in the QRH. If the QRH writes 200 I am gonna drop it at 200. No time delay for FCOM in a dyal HYD.

Lantirn
You are misunderstanding the FCOM. The ECAM which tells you lower gear at 200kts will not do so if slat is extended and you don't refer QRH unless ECAM is completed. So no standardisation is required.

Lantrin, I see how you reached your conclusion. Vilas is correct, I still think.

The QRH is unhelpful. Vilas, imagine:
- with slats out and locked the STATUS has no mention whatsoever of the 200 kt = L/G DN procedure - it is not needed.
- after reviewing status you pull out the QRH summary to brief and later fly the approach
- only to find this:
Attachment 1367.
without any condtions or reference to slat position!

Now, with slats out, if I actively did not respect that printed line "L/G dn at 200 kt", I can vividly see many a TRE looking very deeply into my eyes after a session.

The problem is that summaries are done with reference to QRH.

But i dont see any problem with this. I think airbus has QRH written like this on purpose.

Plus I am going to fly the approach with the QRH (not the ECAM), approach portion of summaries.

I dont have to do all the ECAM actions in sts page, there is a lot to do with the QRH and performance calciulations plus to run the decision model, before I drop the gear.