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SRS mode during windshear - A320

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SRS mode during windshear - A320

Old 25th Feb 2013, 17:23
  #21 (permalink)  
 
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Because referring to the original question the company has set ACCEL ALT at 400'. Therefore there is a chance that you may encounter windshear while SRS is not available.

You are right in saying that the procedure does not mention climb or selecting speed, but then the procedure is assuming that either SRS will be active with FD bars or the take-off will be sans FD or any form of guidance. But then in this situation we do have FD bars but no SRS.

Assume at 380' with SRS active we get Windshear, FD bars on. What happens when we cross 400' i.e. ACCEL ALT. Will the aircraft switch to CLB mode? If it does then villas is suggesting selecting speed to maintain V2+10, and then the FD will give you orders to climb at current speed rather than trying to accelerate. It makes sense although we have to ask ourselves whether OP CLB mode will be able to handle the windshear or not in the same way SRS can, i.e. is it tuned (programmed) to do the job?
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Old 25th Feb 2013, 17:31
  #22 (permalink)  
 
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If you are in SRS then we are all in agreement about the windshear procedure. There are two grey areas first whether in windshear SRS will not change and second if it changes then what you do. None of the manuals give any clue to this. If you find something please reply. I have not yet seen an airline use 400ft acc alt but 800ft is becoming the norm as it does save fuel something like 8kgs. but multiplied by 1000s of takeoffs it amounts to substantial.
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Old 25th Feb 2013, 17:47
  #23 (permalink)  
 
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It's not a grey area.

If not in SRS because of a stupidly low acc alt, set TOGA with AP engaged. If SRS doesn't re-engage - which it possibly will - then do as vilas said - take over. That means AP off, FDs off and pitch for 17.5 degrees using full back stick if necessary.

I say SRS probably will because:

In windshear conditions, flight guidance acts on specially adapted FD pitch orders received from the speed reference system (SRS). The pilot must set go around thrust immediately (which also triggers the FD SRS mode), and follow the pitch order to execute the optimum escape maneuver.
From FCOM DSC-22_40-40 P 1/2

It's an assumption but there is probably a logic that if below 1300 RA, CONF 1 and TOGA is applied then SRS will re-engage. If you'd retracted before 1300 feet RA (extremely unlikely) then I don't think it'd re-engage.

Last edited by WhyByFlier; 25th Feb 2013 at 19:00.
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Old 25th Feb 2013, 18:24
  #24 (permalink)  
 
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WhyByFlier, your procedure will keep your ass safe in that it is something that is in the procedure while vilas' is his own little bit of improvisation, in that sense your method makes more sense to follow. But that's not to say that vilas' technique wouldn't work, someone needs to sit down in the sim and try it out first.

And for that matter, if an airline is going to have a ACCEL ALT below the max windshear warning ALT then the company needs to derive a standardized procedure, unless of course we are all wrong and SRS will reengage with TOGA selected during Windshear
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Old 26th Feb 2013, 00:31
  #25 (permalink)  
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As for the OP, why is your company using an acceleration altitude of 400'?
Fuel costs I have to assume, otherwise it wouldn't make sense.

400' AGL THR RED/ACC ALT, unless there's a noise abatement procedure, or certain airports with special procedures (high alt ops and things like that).
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Old 26th Feb 2013, 01:49
  #26 (permalink)  
 
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Does your company have a standard EO AA? If so what are they using for that?

Also, what is your SOP in the event of an engine failure at what point do they have you commence the acceleration?
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Old 26th Feb 2013, 04:10
  #27 (permalink)  
 
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Let me put things together. I mention again that there is no dispute on windshear procedure as laid down in the manual. In present scenario at 400ft even in windshear LVRCLB will flash (I am certain about it). If windshear warning came before this the thrust levers should not be moved to CLB. Whether SRS will change to CLB we aren't sure yet (I will check it out in SIM). If it changes to CLB we need to reselect TOGA i.e. move Thrust levers CLB and back to TOGA. I agree this will get you the SRS with GA phase. Use the SRS to get out of windshear then tackle GA phase later. This sounds OK.
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Old 26th Feb 2013, 05:59
  #28 (permalink)  
 
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a.pilot,

Maybe Im wrong... but to trigger the Go Around mode by setting the thrust levers on TOGA detent, the aircraft should be in approach mode phase...right?
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Old 26th Feb 2013, 08:09
  #29 (permalink)  
 
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@Flappo,

A.Pilot is correct. You'll get SRS GA TRK anytime TOGA is selected and flap lever at 1 or more - regardless of the flight phase.

Found it out in the sim the hard way as well...
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Old 26th Feb 2013, 10:06
  #30 (permalink)  
 
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Well, I dont remember my last sim session but Im trying to reproduce the same situation on the FMGS trainer and all that I can read on the FMA is MAN TOGA/ SRS /HDG or NAV or RWY plus TAKE OFF phase on the MCDU...
But setting the thrust levers from CLB to TOGA detent, while in approach (approach phase active) then yes, GA mode is activated.

Actually, the SRS will indicate V2+10 on TO and present and no less than Vapp during the GA, two complete different speeds..

So I must have missed something....

Last edited by Flappo; 26th Feb 2013 at 11:24.
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Old 26th Feb 2013, 11:33
  #31 (permalink)  
 
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Hi all

You'll get the SRS below 1300 RA when in TOGA and WS warning.

Vilas, please think about your statement flying in selected speed.
This is so off any procedure.
V2+10 could be far away from best to escape a severe WS. You really want to trade the speed into energy.
Will you brief your F/O on that before departure?
What would he think in case of a windshear monitoring you pulling speed?

We should really stick to company procedures in cases like this.

Best
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Old 26th Feb 2013, 12:21
  #32 (permalink)  
 
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"...V2+10 could be far away from best to escape a severe WS. You really want to trade the speed into energy.."

SRS will provide guidance to maintain V2+10 and/or V2 (engine failure) during the takeoff.
BUT...it will allow the speeds to decrease below these figures in an attempt to maintain a minimum 120 fpm climb.
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Old 26th Feb 2013, 12:48
  #33 (permalink)  
 
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Hi

My understanding is that it is not going to SRS V2+10..... mode.
It's more a SRS WS escape maneuver.


FCOM:
DSC-22_40-40 Windshear Detection Function

In windshear conditions, flight guidance acts on specially adapted FD pitch orders received from the

speed reference system (SRS). The pilot must set go around thrust immediately (which also triggers

the FD SRS mode), and follow the pitch order to execute the optimum escape maneuver.
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Old 26th Feb 2013, 14:12
  #34 (permalink)  
 
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SRS ensures the best aircraft climb performance (TO, GA), however it also ensures a minimum climb out flight path angle. It will provide an adequate speed of reference according the situation, which explains why the procedure ask the PF to follow the FD pitch bar. Thats clear...

During the Take Off the reference speed is V2+10 or V2 and during the Go Around, it will be no less than Vapp.
But I can not find any special speed of reference regarding a Windshear situation...anyway Im speaking from memory and I will take a look on my literature regarding the SRS behaviour under Windshear scenarios...

Thanks for your input.
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Old 26th Feb 2013, 14:41
  #35 (permalink)  
 
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See my latest reply and tell me your views. It appears I am suggesting something non standard that is only because in given scenario nothing is suggested how to get SRS back.
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Old 26th Feb 2013, 14:54
  #36 (permalink)  
 
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Hi Flappo,

FCOM 22-30 Auto Flight Flight Guidance, 80 Common modes, 20 Take Off, SRS
"The SRS guidance law also includes:-
Attitude protection to reduce aircraft nose-up effect during takeoff (​18 or ​22.5 maximum in case of windshear)
Flight path angle protection that ensures a minimum vertical speed of ​120 ft/min
A speed protection limiting the target speed to V2+​15 kt."

I've seen the SRS command a minimum vertical speed of 120 ft/min which caused a speed reduction well below V2.

Hi vilas,
nothing is suggested how to get SRS back.
Reduce to MCT gate and re-select TOGA. Provided you have Flaps 1 or more, you'll get SRS.
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Old 26th Feb 2013, 15:39
  #37 (permalink)  
 
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You really wanna be in TOGA all the time and not playing around with your trust levers. (my opinion only)
Vilas
If you don't have your SRS you just go initially to 17.5 degrees pitch up. (see qrh)
If needed you can pull back that stick as much as you can.
Much better than follow a V2+10 FD (not SRS!) that could guide you in a situation loosing altitude.

Thanks all
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Old 26th Feb 2013, 16:25
  #38 (permalink)  
 
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Windshear

If a/p is on pull heading! You wouldn't want to be turning before out of shear! That's crazy!
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Old 26th Feb 2013, 16:54
  #39 (permalink)  
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Does your company have a standard EO AA? If so what are they using for that?

Also, what is your SOP in the event of an engine failure at what point do they have you commence the acceleration?
EO AA is defined by airline policy at 1500' AFE, except for a very small number of runways that have special requeriments.

SOP in case of an engine failure is to level off at that EO AA and start the acceleration segment.
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Old 26th Feb 2013, 18:39
  #40 (permalink)  
 
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Do you level off at 1500' only as long as the engine is secure of regardless?
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