A320 G+B HYD failure

[che ci dò che ci dò!]

Guys,
does any of you have any idea on the reason why, on the A320, with a G+B hyd failure (both systems not recovered) the use of ATHR is not recommended?
And why the landing gear gravity extension procedure has to be applied at 200 kts? just for a proper anticipation to avoid a big mess in the final part of the approach?
Thanks!

[OPEN DES]

You only have one elevator left so you might not have enough pitch authority left to counteract the pitch moment created by the autothrust. When in manual thrust this pitch moment is more easily controlled/mitigated.

The gear extension also creates a pitching moment which at low speed is harder to counteract due to the reduced pitch authority.

Hope this helps

[CaptainProp]

Lading gear - It is recommended that the landing gear is extended at or below 200kts to get a "feel" of the aircraft in direct law earlier. Below 200kts gives a better pitch control, remember, one elevator and all slats are lost.

"Sluggish" aircraft due to reduced, and slower, flight control surfaces operative. Higher than normal pitch (no slats) and the auto-thrust could end up commanding big thrust changes as that you would be fighting with a "sluggish" slow reacting aircraft and with big control inputs you are putting unnecessary loads on the only operating hydraulic system.....

[South Prince]

QRH Extract looks clear enough:

IF HYD NOT RECOVERED (line not displayed for
a double LO LVL):
A/THR......................................................... ..........OFF
Select the target speed on the FCU. Due to the loss
of slats and some flight control surfaces, the A/THR
may not satisfactorily maintain speed.

FOR LDG............................................... USE FLAP 3
This line is replaced by “FOR LDG : USE FLAP 3
when CONF 3 is selected, as a reminder.
GPWS LDG FLAP 3..............................................ON
 WHEN SPD 200 KT (displayed when slats are
retracted):
L/G.................................................GRVTY EXTN
Refer to PRO-ABN-32 L/G GRAVITY
EXTENSION
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.

:ok: Ciao Ci do che ci do

[Cagedh]

It is recommended that the landing gear is extended at or below 200kts to get a "feel" of the aircraft in direct law earlier. Below 200kts gives a better pitch control, remember, one elevator and all slats are lost. := As soon as the gear comes down, you'll be in direct law. The remaining elevator deflection will be directly proportional to side stick deflection. The higher the speed, the more effective the remaining elevator will be. Not the other way around! So put the gear down AT 200 kts, NOT "At or below" :=

South Prince said it all. The FCOM is clear enough!

Additionally, when in direct law, I as a pilot want to be in manual control of thrust: An increase in thrust will result in a pitch up moment and vice versa. In manual thrust I can anticipate the pitch change and add or reduce thrust more smoothly!
If you let autothrust take care of maintaining the speed, you will be chasing the desired pitch as the pitch varies when autothrust changes the thrust.

[CaptainProp]

Yea yea yea, Cagedh, chill out hu...? Reading my post again I can see it was maybe not that clear but get off your high horses...

Yes, you will be in Direct Law when gear is selected down, I never said anything else either.

The QRH actually says "WHEN SPD 200 KT" "Gear GRVTY EXTN". It actually makes no real difference if you do it @ 210, 190 or "AT" 200.

From FCTM:

"Some minor control difficulties might result from this failure, as no ailerons will operate and only one elevator is available. It is recommended that the landing gear is extended at 200kts to revert sooner to direct law."

Just remember, if you are flying with Cagedh, put the damn thing down AT 200 KT!!

[Cagedh]

@CaptainProp

Who needs to chill out? Who needs to get off his high horse?

I simply pointed out that what you said (below 200, better pitch control) is wrong and that you were giving bad advice by suggesting it would not matter if you put the gear down at 135 kts rather then 200 kts. (or 210, or 195 :ugh:)

Is it really that difficult to admit that you made a mistake or brain fart, rather then getting defensive or feeling insulted when somebody points out your mistake?

[320p]

Noticed this from AFM EMER-29 P 1/4

For approach and landing:
Note: Flaps extend slowly.
Extend landing gear by gravity. Refer to ABN-32 L/G GRAVITY EXTENSION.
Note: If slats retracted, extend landing gear only below 200 kt.

Why does the AFM mention "only below 200kt" (which implies an upper limit ) while the QRH states "when SPD 200 KT,L/G GRVTY EXTN" ?

Thanks