Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

A320 G+B HYD LG extension

Tech Log The very best in practical technical discussion on the web

A320 G+B HYD LG extension

Old 1st Jul 2014, 08:49
  #1 (permalink)  
Thread Starter
 
Join Date: Mar 2012
Location: Having a margarita on the beach
Posts: 2,402
Likes: 0
Received 0 Likes on 0 Posts
A320 G+B HYD LG extension

Hello folks,

apologies if this has been discussed before but couldn't find the specific reference. In the above mentioned failure the procedure is to extend the gear at 200 kias in order to revert to direct law to enhance controllability due to the single elevator remaining. Question here : Why 200 kias ? On the A330 that's the limit speed to get the gear down by gravity, but there's nothing specified for the A320.

Thanks !
sonicbum is offline  
Old 1st Jul 2014, 09:09
  #2 (permalink)  
 
Join Date: Aug 2009
Location: GPS L INVALID
Posts: 578
Likes: 0
Received 0 Likes on 0 Posts
I am not an Airbus driver, but you are basically asking why the procedure tells you to extend the gear at 200KIAS or below even though there is no explicit VLO for the manual extension, correct? I suspect it is supposed to reduce the load on the gear (the nose gear especially), while freefalling, extrapolating from my Boeing knowledge I reckon that the gear doors will stay open, too...
STBYRUD is offline  
Old 1st Jul 2014, 09:15
  #3 (permalink)  
 
Join Date: Jun 2013
Location: Or-E-Gun, USA
Posts: 326
Likes: 0
Received 0 Likes on 0 Posts
What? Please Explain..............

I've read this three times. I'm not a qualified A320 driver, but understand most things. I have No Idea what you are are asking. Please try again... If it makes sense, someone will try to help you.
No Fly Zone is offline  
Old 1st Jul 2014, 09:35
  #4 (permalink)  
 
Join Date: May 2002
Location: Sale
Posts: 374
Likes: 0
Received 0 Likes on 0 Posts
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.
From Abnormal section of the FCOM.
Field In Sight is offline  
Old 1st Jul 2014, 13:36
  #5 (permalink)  
Thread Starter
 
Join Date: Mar 2012
Location: Having a margarita on the beach
Posts: 2,402
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Field In Sight
From Abnormal section of the FCOM.
Thanks Field. I was wondering if these 200 kt were coming out of something.

Cheers.
sonicbum is offline  
Old 1st Jul 2014, 13:38
  #6 (permalink)  
Thread Starter
 
Join Date: Mar 2012
Location: Having a margarita on the beach
Posts: 2,402
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by No Fly Zone
I've read this three times. I'm not a qualified A320 driver, but understand most things. I have No Idea what you are are asking. Please try again... If it makes sense, someone will try to help you.
Hi,

you said it yourself hehe... if you were A320 qualified it would make sense to you as well

Cheers.
sonicbum is offline  
Old 1st Jul 2014, 13:48
  #7 (permalink)  

Dog Tired
 
Join Date: Oct 2001
Location: uk
Posts: 1,688
Likes: 0
Received 1 Like on 1 Post
It so the tail is in the correct trimmed position to allow the single elevator enough authority for the landing flare.
fantom is offline  
Old 1st Jul 2014, 18:10
  #8 (permalink)  
 
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,396
Likes: 0
Received 0 Likes on 0 Posts
Fantom
In G+B fail you have no problem of trim. That happens in G+Y. With G+B fail you have half elevator, at higher speeds normal law works fine but at lower speeds elevators working via LF demand does not give precise feel of elevator control. In direct law you directly move elevators gives better control.
vilas is offline  
Old 2nd Jul 2014, 01:03
  #9 (permalink)  
 
Join Date: Jul 2000
Location: Smogsville
Posts: 1,424
Likes: 0
Received 0 Likes on 0 Posts
I'd imagine during flight test the test pilots found it easier to control the A/C in direct law below 200kts, selecting the gear down in your example forces the system to go in direct law. It's got nothing to do with the gear other than a means to an end.
SMOC is offline  
Old 2nd Jul 2014, 05:16
  #10 (permalink)  
 
Join Date: Jul 2002
Location: brisbane, Australia
Posts: 368
Likes: 0
Received 0 Likes on 0 Posts
Hmmm Since when has Blue been used for the Landing gear ???
fruitloop is offline  
Old 2nd Jul 2014, 08:15
  #11 (permalink)  
 
Join Date: Mar 2012
Location: Dark Side of the Moon
Posts: 1,424
Received 203 Likes on 67 Posts
It hasn't, question was regarding the G+B HYD failure which results in an manual gear extension (due to G) and the single elevator due to the (G+B). It is for the elevator reason that the FCOM directs LG down at 200kts.
Ollie Onion is offline  
Old 2nd Jul 2014, 09:00
  #12 (permalink)  
Thread Starter
 
Join Date: Mar 2012
Location: Having a margarita on the beach
Posts: 2,402
Likes: 0
Received 0 Likes on 0 Posts
Thank You all for your inputs. Further to that another question. The APPR PROC calls for ATHR OFF as due to loss of slats and some flight control surfaces, the ATHR may not satisfactorily maintain the speed. Is it acceptable to disconnect the ATHR upon completing the landing configuration ? Every time I deal with that failure (in the sim) I notice that the ATHR does a pretty good job and the pitch up effect can still be counteracted easily so I tend to keep it till landing conf established to reduce the workload. Got different opinions on that through the years. Thanks !
sonicbum is offline  
Old 2nd Jul 2014, 09:44
  #13 (permalink)  
 
Join Date: Jan 2014
Location: N5109.2W10.5
Posts: 720
Likes: 0
Received 0 Likes on 0 Posts
villas,
In direct law you directly move elevators gives better control.
Agreed.
But using the same logic, why is there not a similar procedure with B & Y SYS LO PR? (R ELEV INOP).
The big differences are no Slats - hence there is a big trim change when Flaps 2 selected. Consequently manual thrust is recommended so that the thrust change couple can be controlled better; and there are no ailerons for roll control with only Y Hyds available,

sonicbum
Is it acceptable to disconnect the A/THR upon completing the landing configuration ?
Well, the QRH says A/THR off early during the procedure, even before reducing speed to below 200 kts. The sim ATHR might be able to cope OK, but it sounds like Airbus want to give the responsibility to the pilots.

Similarly, QRH Flaps/Slat jammed: "A/THR recommended except in the case of a G & B Lo PR warning"

Last edited by Goldenrivett; 2nd Jul 2014 at 12:18. Reason: extra text
Goldenrivett is offline  
Old 2nd Jul 2014, 23:13
  #14 (permalink)  
 
Join Date: Jul 2002
Location: brisbane, Australia
Posts: 368
Likes: 0
Received 0 Likes on 0 Posts
Ollie
My apology for "misreading" the question.
Goldenrivett.
Spoilers for roll control ??
fruitloop is offline  
Old 2nd Jul 2014, 23:20
  #15 (permalink)  
 
Join Date: Jan 2014
Location: N5109.2W10.5
Posts: 720
Likes: 0
Received 0 Likes on 0 Posts
Ollie
Spoilers for roll control ??
Affirm. Only 2 spoilers per wing - not as effective as ailerons hence FCOM
" APPR SPD ... VREF +25 KT
Approach speed must be increased due the loss of ailerons and slats."
Goldenrivett is offline  
Old 3rd Jul 2014, 03:52
  #16 (permalink)  
 
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,396
Likes: 0
Received 0 Likes on 0 Posts
Goldenrivett
Although B+Y also has half elevator it doesn't appear to be that critical. Except AP is not available and landing gear is by gravity extension (since you don't want to risk the only hydraulics) most things are available and therefore in B+Y you remain in NORMAL LAW.Half elevator also has aileron like effect since it is on one side. With no ailerons this may be more difficult to handle in alternate law. Since both slats and flaps are available AC attitude is normal and ATHR control is satisfactory.
vilas is offline  
Old 3rd Jul 2014, 07:41
  #17 (permalink)  
 
Join Date: Jan 2014
Location: N5109.2W10.5
Posts: 720
Likes: 0
Received 0 Likes on 0 Posts
Villas
With G+B fail you have half elevator, at higher speeds normal law works fine but at lower speeds elevators working via LF demand does not give precise feel of elevator control.
Please explain why the same logic does not apply to B & Y SYS LO PR.

Half elevator also has aileron like effect since it is on one side. With no ailerons this may be more difficult to handle in alternate law.
ALT Law is roll direct - same as Direct Law so why would it be more difficult in ALT Law?
Goldenrivett is offline  
Old 4th Jul 2014, 06:23
  #18 (permalink)  
 
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,396
Likes: 0
Received 0 Likes on 0 Posts
Goldenrivett
The difference in the two failures seems to be caused by ailerons.The rolling effect caused by half elevator is same in both cases but in B+Y the ailerons are available and its control in normal law is automatic. In B+G the AC is in pitch alternate and roll direct. Elevator movements through load factor demand in alternate law are likely to cause more rolling which in absence of ailerons only with spoilers 2 and 4 becomes difficult to control. Changing to direct law early is for precise elevator control there by reducing rolling effect.

Last edited by vilas; 4th Jul 2014 at 09:04.
vilas is offline  
Old 4th Jul 2014, 08:31
  #19 (permalink)  
 
Join Date: Jan 2014
Location: N5109.2W10.5
Posts: 720
Likes: 0
Received 0 Likes on 0 Posts
vilas
The difference in the two failures seems to be caused by ailerons.
Partly true. The other differences are A/THR OFF and No Slats and with Hyd B & G SYS Lo PR.

Any induced roll caused by half an elevator and having only wing spoilers should be easily controllable with some rudder input.

I think the big difference is caused by going from a clean wing to F2 below 200 Kts. There is a big shift aft of C of L causing a nose down pitch couple (due to Flaps 15 but no Slats at 22). If it exceeded the rate at which ALT LAW in pitch (with only half an elevator) could control the pitch change, then the nose would lower. If A/THR was on, any speed increase would cause a thrust reduction and a further nose down couple making control more difficult.

I think Airbus discovered the problem was better controlled using manual thrust & Direct Law feed back to the pilots to appreciate the trim change necessary.
Goldenrivett is offline  
Old 4th Jul 2014, 10:14
  #20 (permalink)  
 
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,396
Likes: 0
Received 0 Likes on 0 Posts
The old instructor support had this line:
"Landing gear has to be extended by gravity (paper c/l) and NWS is systematically lost. 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 approach after landing gear extension may require (ECAM procedure) a voluntary disconnection of the ATHR (G + B) in order to obtain an easier a/c pitch control during approach and go around."
It appears it had more to do with gear extension than flaps. ATHR off course will complicate matters because of degraded pitch control. What happens if you lower flaps2 with gear up can be checked in the SIM.
vilas is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.