A320 G+B Hydraulic failure

[Speedwinner]

Hello folks,

I have a specific question preparing my sim ride: the qrh procedure said to extend the gear at 200kts. So why is it 200 kts? Any technical reasons for that? Any reason at all?

Thanks!

Sw

[ESQU]

From the FCOM

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

[galaxy flyer]

As an old IP used, "give 'em books, they'll eat the papers".

GF

[Speedwinner]

I know. That's why I'm asking. Maybe there are pilots who accelerate to 200 kts to drop the gear because it's written there. So no need for that right. I'm not sure why they wrote instead: below 200 kts gravity gear extension can be performed

[I-2021]

Hi Speedwinner,

lots of interesting stuff here (http://www.pprune.org/tech-log/502629-a320-g-b-hyd-failure.html) and here (http://www.pprune.org/tech-log/542750-a320-g-b-hyd-lg-extension.html)

:ok:

[Goldenrivett]

So why is it 200 kts? Any technical reasons for that?

Flaps 2 speed limit.

If the Slats are at position 0, selecting Flaps 1 does not give you any config change (due Slats jammed). When you select Flaps 2 there is a big pitch & trim change required to maintain level flight. (You can often feel the aircraft struggle to maintain 1g in Normal Law when going from Slats 1 to F2). Don't be surprised if you trigger a momentary "Stall Stall" warning. It's due to the +ve delta g (which you won't feel in the sim) as the flaps run out and being closer to the stall due no slats. As you reduce the pitch attitude, you'll reduce the g and the stall warning will cease.

ECAM has the conditional line:
"WHEN SPD 200 KT (displayed when slats are retracted):
L/G ...... GRVTY EXTN"
whereas the QRH does not mention the condition (to keep it simple).

When you are manually flying in Direct Law, you will feel the forces required better (when only the Flaps run from 0 to position 2), be able to move the Stab Trim faster than the automatics can and balance the required manual thrust.
We used to call it "flying the aircraft" in the old days.

[320p]

Thanks for the above explanation .
However, as per AFM EMER-29 P 1/4 :
Note: If slats retracted, extend landing gear only below 200 kt
So, as per AFM, lowering landing gear has an upper speed limit and not at 200 kt as per FCOM.
There appears to be some discrepancy .

[Goldenrivett]

There appears to be some discrepancy .
Check the revision date of your AFM. If there is more than one reference to the same procedure, you will often notice a difference until they are all aligned. But don't hold your breath waiting.

I have an old copy of QRH (2003) and the G+B SYS LO PR Summary recommends that you delay the L/G Gravity Extension until you have decelerated to the Calculated VAPP.

In the light of crew and aircraft performance over the years, Airbus has changed some of its recommended procedures.

[Togue]

Speedwinner,

From FCOM PRO-ABN-29 P20/28 9 SEP 15 "Extend the landing gear at 200kt to revert sooner in direct law. This provides, below 200kt, a better pitch control than in alternate law with one elevator lost and all slats lost"

[Escape Path]

I know. That's why I'm asking. Maybe there are pilots who accelerate to 200 kts to drop the gear because it's written there. So no need for that right. I'm not sure why they wrote instead: below 200 kts gravity gear extension can be performed

In the sim I've never had this particular failure below 200kts. You're making sense of what you are saying, but I think the logic of how the procedure is written is that you will get to this part under deceleration so the "below 200kts" it's sort of implied.