SRS mode during windshear - A320
 

Hello everybody, today I was thinking about what the A320 would do if you have a windshear encounter, assuming managed lateral and vertical modes and AP on, and I'm struggling to really understand what would happen given this situation:

Let's assume the following conditions: takeoff is done with TOGA thrust, flaps 1, and THR RED/ACC ALT is defined by airline policy at 400' AFE. So, everything normal during rotation, AP is engaged, and while below THR RED/ACC ALT (both set on the mcdu at 400' AFE), you start experiencing windhsear conditions. The FCOM procedure states:

"Windshear during initial climb:

THR LEVERS at TOGA: SET OR CONFIRM
AP (if engaged): KEEP
SRS ORDERS: FOLLOW
DO NOT CHANGE CONFIGURATION (SLATS/FLAPS UNTIL OUT OF SHEAR)"

Given those takeoff conditions, at the moment of the windshear encounter all the pilot would have to do is monitor the AP's performance in following SRS orders (TOGA and AP already set, SRS mode engaged, flaps at 1). But, from what the FCOM says, SRS mode would disengage at 400' AFE, and CLB mode would engage, thus losing the SRS guidance and protections, making the whole windshear procedure invalid as you can't "follow SRS orders".

If we take a look at the SRS disengament conditions, it says:

"Disengagement Conditions:

The SRS mode disengages:

- Automatically, at the acceleration altitude (ACC ALT), or if ALT* or ALT CST* mode engages (above 400 ft RA).
- If the flight crew engages another vertical mode
- If the flight crew selects a speed while in SRS mode: SRS reverts to OP CLB mode, and a triple-click aural warning is heard."

And for the CLB mode, it says:

"Engagement conditions:

CLB mode automatically engages when the aircraft reaches ACC ALT, or sequences a waypoint with an altitude constraint while the CLB mode is armed".

From what I remember from my simulator sessions, SRS mode stays engaged during a windshear encounter, but I don't know if that's because it was a FLEX takeoff, and that would force the pilot to engage TOGA thrust, thus engaging SRS again; or because there's another condition I am not able to find in the FCOM that makes SRS mode to stay engaged during a windhsear encounter.

I hope I am making any sense, and would really appreciate some insight into this.

Regards!

PWS only valid up to 1500 Feet. Reactive WS up to 1300 Feet.

Acceleration altitude (2 engines) is typically 1500 Feet (1000 Feet in easyJet).

SRS changes to CLB at acceleration altitude. Acceleration altitude is limited to single engine acceleration altitude so 400 feet is extremely unlikely.

What's your problem?

My airline defines both THR RED and ACC ALT at 400' AFE. So the scenario I described is absolutely possible.

What I want to know is why SRS stays engaged during a windshear encounter and the application of the correct procedures (not sure if that's what really happens), given the fact that it should change from SRS to CLB mode due to the reasons I wrote on my previous post.

There is no reason for SRS to remain engaged beyond acceleration altitude.What would happen beyond acc.alt is as you correctly said SRS changes to CLB and that means acceleration. In windshear 400 ft is too low for that so pull speed and fly selected speed till out of windshear then go managed. Do not change configuration in windshear.

Some of the worst advice I've ever seen given on pprune there by vilas. Someone doesn't know their memory items. Without SRS you'd take AP off, pitch to 17.5 degrees with TOGA and use full back stick if needed.

Out of interest, which company are you with?

F/D not available
 

My latest QRH revision states:

Note:
1.If engaged, the autopilot disengages when α is greater than α prot.
2.If the FD bars are not available, use an initial pitch attitude up to 17.5 ° with full backstick, if necessary. If needed, to minimize the loss of height, increase this pitch attitude.

So, while the F/D is still available it is not in the desired mode, so I would have to agree with WhyByFlier, disengage AP and fly a max attitude of 17.5deg Nose up, I'd also keep a good eye on the VSI to keep a positive ROC which is what you need and if you get to a full aft stick deflection then so be it.

I think this applies unless there is a logic in the Flight Envelope part of the FAC where the Windshear Warning would override the CLB engagement at Acceleration Altitude.

If such logic exists I don't know of it, but it would not surpise me if it is there.

"I think this applies unless there is a logic in the Flight Envelope part of the FAC where the Windshear Warning would override the CLB engagement at Acceleration Altitude."

That would be the optimal behaviour of the FMS, and it would explain why I have the notion in my mind that the SRS keeps engaged during windshear procedures (I may be wrong hehe).

WhyByFlier,

Vilas claims to be ex Air India and an A320 SFI.. sounds about right for those AI boys!:E

He or she might be a great pilot and more qualified than me but that procedure that was offered is non standard, incorrect and less than optimum. In easy it'd be a repeat in the sim for it and on the line it'd be a meeting and new underwear for the captain.

Found the following:

"Auto Flight, Flight Augmentation, Windshear Detection Function, Guidance:

In windshear conditions, the flight guidance acts on specially adapted FD pitch orders received from the speed reference system (SRS). The pilot must set go around thrust immediately (wich also triggers the FD SRS mode), and follow the pitch order to execute the optimum escape maneuver".

So, from that text and the memory item that states that TOGA thrust must be set or confirmed, and then follow the SRS orders, I assume that the FMGS "knows" you entered a windshear condition and thus keeps or re-engages SRS in the scenario I first described.

That may be the logic that AVApilot thought might exist.

Any other thoughts?

WINDSHEAR (FCOM-PRO-ABN-80 P80, QRH-ABN-80.15 OM B 2.3.90.10)

A red flag "WINDSHEAR" is displayed on each PFD associated with an aural synthetic voice "WINDSHEAR" repeated
three times. If windshear is detected either by the system or by pilot observation, apply the following recovery technique:
¦ At take-off:
* If before V1:
The takeoff should be rejected only if significant airspeed variations occur below indicated V1 and the pilot decides that there is sufficient runway remaining to stop the airplane.
* If after V1:
Announce: "WINDSHEAR TOGA"
THR LEVERS TOGA
REACHING Vr ROTATE
SRS ORDERS FOLLOW


Airborne, initial climb or landing:

Announce: "WINDSHEAR TOGA"
THR LEVERS AT TOGA SET OR CONFIRM
AP (if engaged) KEEP
SRS ORDERS FOLLOW (This includes the use of full back stick, if demanded.)

Note:
1. If engaged, the autopilot disengages when is greater than prot.
2. If the FD bars are not available, use an initial pitch attitude up to 17.5° with full backstick, if necessary. If needed, to minimize the loss of height, increase this pitch attitude.
DO NOT CHANGE CONFIGURATION (SLATS/FLAPS, GEAR) UNTIL OUT OF SHEAR.
CLOSELY MONITOR FLIGHT PATH AND SPEED.
RECOVER SMOOTHLY TO NORMAL CLIMB OUT OF SHEAR.

WINDSHEAR RECOVERY
The best defence against a windshear encounter is to avoid it in the first place. A pilot should
use his knowledge and experience combined with weather reports to assess the possibility of
encountering windshear and plan accordingly. The weather radar may also be a useful tool as
windshear is often associated with thunderstorms and microburst. The use of managed speed
and the groundspeed mini function will give added protection against windshear in strong winds.
The A320 is fitted with two types of Windshear Protection;
　
　
　
REACTIVE WINDSHEAR:
The FACs generate the windshear warning whenever the predicted energy level for the aircraft
falls below a predetermined threshold.
The protection envelope is from just after lift-off until 1300ft on take-off and from 1300ft to 50ft
for landing. For both cases, at least CONF 1 must be selected.
A red "WINDSHEAR" flag is displayed on each PFD (for a minimum of 15 seconds) associated
with an aural warning "WINDSHEAR" repeated 3 times. If windshear is detected either by the
system or by pilot observation, the pilot must take immediate action:
• Apply TOGA
• Call "WINDSHEAR TOGA"
• Follow SRS orders closely (keep A/P if engaged)
• DO NOT change the aircraft configuration
If the flight directors are not available, then the pilot should pitch up to 17.5° nose up. Should thpilot require it, the use of full back sidestick is available. This may trigger Alpha Floor protection
Both pilots should monitor the Pitch, IAS, V/S and the actual W/V during the encounter, as theyare a good indication of the aircraft’s energy state.
In the unlikely event of encountering windshear during the take-off roll, the takeoff should only brejected if significant airspeed variations occur below V1 and the pilot decides that there is
sufficient runway remaining to stop the airplane. Due to changes in the acceleration of the
airplane during a windshear incident, an overrun may occur if a rejected take-off is actioned.

PREDICTIVE WINDSHEAR:
The weather radar has a Predictive Windshear System (PWS) that scans the airspace ahead of
the aircraft up to a range of 5 miles ahead for windshears. The PWS system detects any
‘Doppler shift’ in the pattern of rain droplets and so will not detect windshears in dry atmospheric
conditions.
The protection envelope available for alerts is from the start of the take-off roll up to 100kts, and
then from 50ft to 1500ft and from 1500ft to 50ft for landing.
When the system detects a windshear, a Warning, Caution or Advisory is triggered.
　
　
Warning:
On the PFD: ‘W/S AHEAD’ in red.
On the ND: Windshear icon.
Aural warning: on take-off: "WINDSHEAR AHEAD" twice.
on landing: "GO-AROUND WINDSHEAR AHEAD".
Pilot action: on take-off: Reject take-off.
when airborne: Thrust levers TOGA and turn to avoid the windshear icon.
Follow SRS and normal clean-up provided windshear is not entered.

(On landing, if a positive verification is made that no hazard exists,
the warning may considered cautionary – otherwise go-around.)
Caution:
On the PFD: ‘W/S AHEAD‘ in amber.
On the ND: Windshear icon.
Aural warning: "MONITOR RADAR DISPLAY"
Pilot action: Apply precautionary measures as indicated in ‘FCOM -Supplementary
techniques’
　
　
Advisory:
On the PFD: Nil.
On the ND: Windshear icon.
Aural warning: Nil.
Pilot Action: As Caution.

INDICATIONS ON THE ND:
　

The predicted windshear area is indicated by a red and black icon and two yellow radial lines.
Windshear information is available in ARC and ROSE ND modes.
When the ND range is set above 10 NM, a W/S SET RNG 10 NM message appears, requesting
the crew to adjust the ND range. It is displayed even if the weather radar is switched off,
provided the WINDSHEAR switch on the weather radar panel is set to AUTO.

　
　
　

So do you agree that the answer to my question is what I posted before about the Windshear Detection Function? From what I now understand, it provides a special kind of SRS, and the FG part of the FMGC knows it is in the middle of a windshear encounter, thus modifying the SRS orders, and keeping it engaged.

I'm still not 100% sure, just the best answer I have right now.

Cheers.

I may not have answered the question but my answer gives the correct memory items in the event the aircraft/ FDs/ AP do not respond the way you'd expect.

I fly for easyJet.

i'm sorry, but can anyone remember if there is a flashing LVR CLB during the windshear maneuver, and if theres none, when does it appear.

thanks

IIRC, 'LVR CLB' is flashing on the FMA above the acceleration alt and the FD maintains SRS till the TL's are retarded back to the CLB detent. I can be mistaken, though...

Dear WhyByFlier

Memory items are not rocket science everyone includingKowalsky knows them. TOGA was power used for takeoff itself so what’s the pointrepeating it. He has asked for solution in a specific situation, that is theacceleration altitude is 400 feet so SRS has changed to CLB. All Airbusdocuments and DVD’s assume that the acceleration altitude as 3000 feet (noise abetment).Therein lies the problem. No Airbus document gives a procedure for this. It tellsyou to keep the AP on, it tells you to fly the FD but in SRS. Myfriend PT6A who went out his way to find my pedigree (I am honored really) hasgiven a full page reference from FCOM which is completely irrelevant to thepresent case since it keeps on repeating follow SRS, and if AP is on keep iton, because in our case the SRS has changed to CLB and if you do nothing withAP on the AC pitch will reduce to accelerate and may be fatal. Your aggressive suggestionof flying 17.5 has already been answered by a Pilot albeit in your very ownstyle. Since there is no official procedure we have to guess. My suggestionstops the acceleration, allows you keep the AP on and if doesn’t meet therequirement, Airbus golden rule “take over” go above the FD’s, full back stickif required. PT6A can you honestly say you answered the question? Lastly myinterest in pprune is purely professional. Many questions like the present onemake you think out of the box. I don,t flash my experience or background nor Itry to show off if that’s your style good luck to you. In aviation far too manypilots have laughed far too soon and had to eat their hats. So cheer up.

Out of interest Are you a captain yet?

I'm not bickering and I'm not having a go but the question was about no SRS IN A WINDSHEAR caused by a very low thr red/acc alt.

If you think selecting speed with AP engaged in a windshear because there's no SRS is a good idea then I think you need to approach either your training department or Airbus.

I'm not a captain yet no.

Yes this was my initial thought but we mustn't mix up ACCEL ALT with THR RED. The Situation you mention above is THR RED, not ACCEL ALT. At THR RED you will get flashing LVR CLB message but after selecting CLB you will still be in SRS mode. Once at ACCEL ALT aircraft switches to CLB mode and accelerates. (ref. DSC-22_30-80-20 p1/4 SRS Disengagement Conditions)

What villas is saying is not unreasonable, the key in the windshear situation is to use all the aircraft energy possible for a climb. Pulling speed at ACCEL ALT will maintain v2+10 or whatever SRS had commanded and will get the FG to try and give you the best climb possible with TOGA power. In windshear that's all you can hope for, if TOGA plus max nose up is not going to give you a positive climb then there's not much else left to do but start praying. In my humble opinion this will do the job. I also don't see how TOGA and 17.5degrees is wrong either, both should work, no? I think that selecting OP CLB is a better option than CLB.

The only thing left to analyse now is the difference in behavior between CLB vs. SRS, and are there some inherent differences that would render the CLB mode logic incapable of dealing with windshear (vs. SRS logic, which is obviously programmed to deal with it). SRS limits nose up to 22.5 degrees with windshear, not sure about

Vilas,

I actually think the information I posted does answer the question. As it is tailored company specific information. In our company the standard acceleration altitude is 1000' yet the guidance from our 3 documents remains the same (FCOM, OM-B and Airbus Training Guide) to follow the SRS.

From this I deduce that in the event of wind shear being detected.. The aircraft would remain in SRS.

As for the OP, why is your company using an acceleration altitude of 400'?

(400 being the minimum regulatory acceleration altitude - but far from necessary or desirable in the A-320)

We're talking about a windshear in the Airbus not forgetting to put an NADP 1 in the box. Selecting speed with AP in a windshear is not an appropriate response.

From the QRH:

A red flag “WINDSHEAR” is displayed on each PFD associated with an aural synthetic voice “WINDSHEAR” repeated three times. If windshear is detected by pilot observation, apply the following recovery technique: ■ At takeoff

■ If before V1

The takeoff should be rejected only if significant airspeed variations occur below indicated V1 and the pilot decides that there is sufficient runway remaining to stop the airplane.

■ If after V1 THR LEVERS...................................................... ...................................TOGA REACHING VR.......................................................... .........................ROTATE SRS ORDERS...................................................... .............................FOLLOW If necessary, the flight crew may pull the sidestick fully back.

Note: 1. Autopilot disengages if the angle of attack value goes above α prot. 2. If the FD bars are not displayed, move toward an initial pitch attitude of 17.5°. Then, if necessary, to prevent a loss in altitude, increase the pitch attitude.

■ Airborne, initial climb or landing THR LEVERS AT TOGA........................................................ SETORCONFIRM AP (if engaged).................................................... .........................................KEEP SRS ORDERS...................................................... ..................................FOLLOW If necessary, the flight crew may pull the sidestick fully back.

Note: 1. Autopilot disengages if the angle of attack value goes above α prot. 2. If the FD bars are not displayed, move toward an initial pitch attitude of 17.5°. Then, if necessary, to prevent a loss in altitude, increase the pitch attitude.

DO NOT CHANGE CONFIGURATION (SLATS/FLAPS, GEAR) UNTIL OUT OF SHEAR. CLOSELY MONITOR FLIGHT PATH AND SPEED. RECOVER SMOOTHLY TO NORMAL CLIMB OUT OF SHEAR.


Where does selecting speed come into this?

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?

PT6A
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.

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:

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.

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

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).

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?

a pilot
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.

a.pilot,

Maybe I´m 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?

@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...:ugh:

Well, I don´t remember my last sim session but I´m 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....

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

"...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.

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.

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. That´s 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 I´m speaking from memory and I will take a look on my literature regarding the SRS behaviour under Windshear scenarios...

Thanks for your input.

CL 30 FL
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.

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,
Reduce to MCT gate and re-select TOGA. Provided you have Flaps 1 or more, you'll get SRS.

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

Windshear
 

If a/p is on pull heading! You wouldn't want to be turning before out of shear! That's crazy!

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.

Do you level off at 1500' only as long as the engine is secure of regardless?