a320 stall recovery

[flying jocks]

Looking for an expert's opinion (a lot of you out there) regarding the correct flap usage during an approach to landing stall in the bus - A320.

The common wisdom is that we leave the flaps where they are whilst reducing the AofA until out of the stall, whereupon power can be applied once the wings are level and then recover the flight path before flaps are retracted.

Reading the FCTM, flaps actually cause the critical angle of attack to reduce albeit with a considerable lift benefit, but the drag with the flaps down and the poorer climb performance subsequently got me thinking that an immediate retraction to flaps 1 might be better. The FCTM mentions that slats have a big benefit in terms of critical angle of attack, but the guidance for recovery is vague. The advice to reduce attack angle is stated even if this results in height loss, therefore do not try to preserve height and certainly do not try powering out of the stall as people did in the old days.

in a nutshell, flaps 1 is mandated for clean config. stalls below FL200, but I would argue that once the angle of attack has been reduced and there are no more stall symptoms (wings level and speedbrake retracted), increasing thrust and retracting flaps to config 1 would speed up the recovery and subsequent loss of altitude because:-

1. Flaps don't instantly retract - they take quite a few seconds to disappear so they are producing lift whilst in the recovery and speed sharply increasing
2. Less likelihood of secondary stalling as the critical angle of attack on average increases (critical angle lowers with flaps and increases with slats leading to an overall increase as the flaps disappear)
3. Better climb performance post recovery

[AerocatS2A]

I would leave them where they are, as per FCOM!

1. The flaps retract quicker than the speed increases.
2. The critical angle may increase but the lift you get is less, so to maintain the lift you had prior to retracting flaps you need to increase AoA past the critical angle and you end up in a secondary stall.
3. Once you have recovered, you are certainly free to retract flap on schedule to improve climb performance.

Don’t over think it. If it was a good idea to retract flaps then that would be the procedure.

[flying jocks]

Thanks AerocatS2A,

No specific reference in FCOM that I can find for stall in approach/landing configuration. Obviously to prevent secondary stalls, the alpha lock function engages with and attack angle greater than 8.5 degrees on the non-NEO aircraft and speeds less than 148 KTS should flaps handle be retracted completely. The system allows slat retraction to zero once AOA is less than 7.6 and speed greater than 154 KTS which is not very high!!

Flap 1 MUST be selected below FL200 is all that I could find when clean

Normally stall warning in alternate law occurs above 100 KIAS especially in a turn to final say with increased load factor present and full stalls are never practised in the simulator due to lack of aerodynamic data.

https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/1487x1147/image_1_eeba383abd40a7eca3a92347e022c4684343cda8.jpg

[Fursty Ferret]

Good point, but by retracting the flaps you also retract the slats and negate the benefits. If you're in alternate law you'll be flap 3 anyway.

[vilas]

There are a few discussions by Airbus on the subject. According to that selection of Flap1 is not a part of stall recovery but it's a part of flight path recovery. If flaps were in Landing configuration they should be left where they are till you start recovery of flight path then it should be like a GA procedure.

[flying jocks]

As far as rudimentary testing (I'm no test pilot) goes, I practised three scenarios more than 5 times each in the simulator a few days ago.

1. approach to stall in landing configuration with no flap retraction at all and same conditions for recovery lead to a slight increase (100 feet) in height loss - TOTAL height loss from 3000 AMSL = 600 ft
2. approach to stall in the landing configuration with flap retracted one step (similar to go-around) had a 500 ft height loss
3. approach to stall with flaps retracted to config. 1 from config. 3 had a 50 ft increase in height loss on average but a quicker altitude recovery post stall.

I am wondering why the approach configuration stall is not actually prescribed (from what references I can find). It maybe because there is very little in it and Airbus has decided to only paint 'red lines' e.g flaps 1 must be selected below FL200 in their FCTM.

The key points obviously are to reduce AofA first in all cases until stalling conditions have stopped, then follow the rest of the stall recovery procedure.The FCTM talks about prioritising this over height loss. However it also talks about preserving lift which the flaps certainly do but excessive drag might hinder the recovery.

[vilas]

Stall recovery is a serious business and a line pilot who's only association with this phenomenon is in the Simulator is not qualified to change it based on his Simulator experience. It's test pilot recommended procedure just stick to it. Already enough discussion on the subject has taken place between the manufacturer and Airlines. Do you retract flaps in windshear? Why not?

[RVF750]

As above. Not an airbus driver but the same applies to all commercial aircraft. They are flown to all sorts of corners of the envelope by VERY experienced test pilots. Risks are discussed beforehand and things like parachutes, CoG changes and such like are made. They also make maneuvers like this bit by bit as they measure effects and suchlike.

We are not privy to this. Just the end result. They know what they can do, what the aircraft can do. They apply factors to both to achieve a level of safety for the dare I say it lowest expected experienced and able pilot. That's not you, or i, but rules are rules for a reason and it's expected you will follow SOP to ensure you are safe. Second guessing and over thinking these things is not airmanship. It's more a spurs and lasoo kind of thing IMHO. Flame me if you will. But at the subsequent enquiry, your actions will be judged..... just saying.

[flying jocks]

As above. Not an airbus driver but the same applies to all commercial aircraft. They are flown to all sorts of corners of the envelope by VERY experienced test pilots. Risks are discussed beforehand and things like parachutes, CoG changes and such like are made. They also make maneuvers like this bit by bit as they measure effects and suchlike.

We are not privy to this. Just the end result. They know what they can do, what the aircraft can do. They apply factors to both to achieve a level of safety for the dare I say it lowest expected experienced and able pilot. That's not you, or i, but rules are rules for a reason and it's expected you will follow SOP to ensure you are safe. Second guessing and over thinking these things is not airmanship. It's more a spurs and lasoo kind of thing IMHO. Flame me if you will. But at the subsequent enquiry, your actions will be judged..... just saying.

This and the previous quote - I DO share your concerns and am not making policy (THANKFULLY) just curiosity. As I said in my last quote, the standard stall recovery procedure is to be adhered to. If you have any official references as to what to do in the approach config. stall then now is the opportunity to share them. I was hoping to put this matter to sleep by now whilst it is getting late in the evening. Anyhow, thank you for your commentary and making aviation a safer place.

[Genghis the Engineer]

I'm not an A320 expert, so just looking in as somebody who has read a lot. This seems to be an unformatted version of a very well regarded paper on this topic from RAeS' Aeronautical Journal a couple of years ago, that may interest most people here.

http://sftentx.com/files/75234188.pdf

G

[Tail-take-off]

Why have we stalled? Probably because we’ve lost situational awareness of speed, attitude, thrust etc. Is this a good time to be making complex assessments of whether or not it would be beneficial to change config? Probably not, and I suspect that this is why Airbus have kept the procedure a simple rule based one!

The OP might well be right about his simulator tests but will he have the capacity to remember it all mid inadvertent stall? I doubt I would!

[Tasyery]

Good point, but by retracting the flaps you also retract the slats and negate the benefits. If you're in alternate law you'll be flap 3 anyway.
You are right,this has both advantages and disadvantages.

[flying jocks]

All great replies - Thanks.

As to why we have stalled in low level - Loss of SA is a prime suspect without doubt including inadvertent wake turbulence encounter etc. Lots of assumptions can be made as to when the approaching stall would otherwise take place, but on a normal approach with a downgraded flight control law, one would assume that ALL reasonable precautions have taken place to avoid stalling with effective pilot monitoring being optimum. Final flap config. being reached before 1000 AAL. (earlier e.g dual hydraulic failure)

Casting one's mind back to PPL days, it was the procedure to remove the final stage of flap during a landing config. stall straight after power increase, then wait for positive climb i.e the recovery phase for the remaining flap & gear. But I share the view that keeping things simple during loss of SA is probably best.

Thank you all

https://www.pprune.org/images/statusicon/user_offline.gif https://www.pprune.org/images/buttons/report.gif (https://www.pprune.org/report.php?p=10552028) https://www.pprune.org/images/misc/progress.gif Edit (https://www.pprune.org/editpost.php?do=editpost&p=10552028) Quote (https://www.pprune.org/newreply.php?do=newreply&p=10552028) Quick Reply (https://www.pprune.org/newreply.php?do=newreply&p=10552028)flying jocksView Public Profile (https://www.pprune.org/members/14557-flying-jocks)Send a private message to flying jocks (https://www.pprune.org/private.php?do=newpm&u=14557)Find More Posts by flying jocks (https://www.pprune.org/search.php?do=finduser&u=14557)Add flying jocks to Your Contacts (https://www.pprune.org/profile.php?do=addlist&userlist=buddy&u=14557)https://www.pprune.org/images/statusicon/post_old.gif 22nd Aug 2019, 22:12 #10 (https://www.pprune.org/10552068-post10.html) (permalink (https://www.pprune.org/tech-log/624779-a320-stall-recovery.html#post10552068))Genghis the Engineer (https://www.pprune.org/members/13027-genghis-the-engineer)Join Date: Feb 2000Location: UKPosts: 13,599I'm not an A320 expert, so just looking in as somebody who has read a lot. This seems to be an unformatted version of a very well regarded paper on this topic from RAeS' Aeronautical Journal a couple of years ago, that may interest most people here.

http://sftentx.com/files/75234188.pdf

Ghttps://www.pprune.org/images/statusicon/user_offline.gif https://www.pprune.org/images/buttons/report.gif (https://www.pprune.org/report.php?p=10552068) Quote (https://www.pprune.org/newreply.php?do=newreply&p=10552068) Quick Reply (https://www.pprune.org/newreply.php?do=newreply&p=10552068)Genghis the EngineerView Public Profile (https://www.pprune.org/members/13027-genghis-the-engineer)Send a private message to Genghis the Engineer (https://www.pprune.org/private.php?do=newpm&u=13027)Send email to Genghis the Engineer (https://www.pprune.org/sendmessage.php?do=mailmember&u=13027)Find More Posts by Genghis the Engineer (https://www.pprune.org/search.php?do=finduser&u=13027)Add Genghis the Engineer to Your Contacts (https://www.pprune.org/profile.php?do=addlist&userlist=buddy&u=13027)https://www.pprune.org/images/statusicon/post_old.gif 23rd Aug 2019, 06:29 #11 (https://www.pprune.org/10552201-post11.html) (permalink (https://www.pprune.org/tech-log/624779-a320-stall-recovery.html#post10552201))Tail-take-off (https://www.pprune.org/members/183332-tail-take-off)Join Date: Jul 2007Location: taking up the holdAge: 49Posts: 780Why have we stalled? Probably because we’ve lost situational awareness of speed, attitude, thrust etc. Is this a good time to be making complex assessments of whether or not it would be beneficial to change config? Probably not, and I suspect that this is why Airbus have kept the procedure a simple rule based one!

The OP might well be right about his simulator tests but will he have the capacity to remember it all mid inadvertent stall? I doubt I would!https://www.pprune.org/images/statusicon/user_offline.gif https://www.pprune.org/images/buttons/report.gif (https://www.pprune.org/report.php?p=10552201) Quote (https://www.pprune.org/newreply.php?do=newreply&p=10552201) Quick Reply (https://www.pprune.org/newreply.php?do=newreply&p=10552201)Tail-take-offView Public Profile (https://www.pprune.org/members/183332-tail-take-off)Send a private message to Tail-take-off (https://www.pprune.org/private.php?do=newpm&u=183332)Send email to Tail-take-off (https://www.pprune.org/sendmessage.php?do=mailmember&u=183332)Find More Posts by Tail-take-off (https://www.pprune.org/search.php?do=finduser&u=183332)Add Tail-take-off to Your Contacts (https://www.pprune.org/profile.php?do=addlist&userlist=buddy&u=183332)https://www.pprune.org/images/statusicon/post_old.gif 23rd Aug 2019, 08:28 #12 (https://www.pprune.org/10552265-post12.html) (permalink (https://www.pprune.org/tech-log/624779-a320-stall-recovery.html#post10552265))Tasyery (https://www.pprune.org/members/490894-tasyery)Join Date: May 2019Location: KoreaPosts: 9Quote:Originally Posted by Fursty Ferret https://www.pprune.org/images/buttons/viewpost.gif (https://www.pprune.org/tech-log/624779-a320-stall-recovery.html#post10550565)Good point, but by retracting the flaps you also retract the slats and negate the benefits. If you're in alternate law you'll be flap 3 anyway.You are right,this has both advantages and disadvantages.https://www.pprune.org/images/statusicon/user_offline.gif https://www.pprune.org/images/buttons/report.gif (https://www.pprune.org/report.php?p=10552265)

[Santiago60]

The main issue in a stall is the angle of attack, not the speed. In other words, you can not have a stall without having the critical angle of attack, but you can stall the plane even with good speed.

if I understand correctly, the purpose of the excercise is the best way to recover from a stall, NOT which is the best or faster method to increase the speed.

As you know, the more flaps involved, the lower angle of attack. It doesn’t matter if you don’t have the best performance.
We have to focus which is the main task: recover from a stall, or how to loose minimum altitude, or how the best climb performance is reached.

I think, from what I read, that the main purpose in your exercise research is “How to better recover from a stall”.

Cheers
​​​​​​,

[JABBARA]

Just a little contribution away from discussion. Extract from old FCOM of A 330 1g Stall speed (Vs1g) for 200t are as below:
Conf Clean : 155 K
Con 1 = 138 k
Con 1+F =129 K
Conf 2 = 122.5 K
Conf 3 = 120 K (Gear Down)
Conf 3 = 119 (Gear Up)
Conf Full = 116 K (Gear Down)

So difference of Vs1g betwen Conf 3 Gear Up and Conf 1+F is 10K. So if we are at the edge of stall, retracting Flaps from Conf 3 to Conf 1+F requires 10K speed increase to keep critical AOA (= whatsoever Max AOA for current configuration).
Intuitively, we may think, retracting the flaps and reducing their parasite drag may easily help to accelerate through this 10 K . But in fact it may not. Because at this critical stage (at very low speed) most of the total drag consist of from Induced drag, not parasite drag which is mostly result of dynamic pressure (i.e speed). Therefore retracting flap may at least momentarily may increase total drag rather than reducing it. So my humble option is to keep conf as is (as advised by memory item) to optimize Stall Recovery path.

[Fursty Ferret]

Since the 1g stall requires continual backstick I wonder if the aircraft would recover from a stall hands off if you did go from F3 to 1. The speed for F3 is lower, sure, but the critical angle is less too.

[vilas]

There's no VS1g stall. There's VS1g speed which is CL max speed. Stall occurres at less than 1g. There's VS1g speed in FBW which is used for calculation of other speeds in protected FBW aircraft instead of VS in unprotected aircraft. If you're discussing stall then it will only happen in alternate law. There you can go past CLmax to n<1 which is the VS.

[JABBARA]

There's no VS1g stall
There is Vs1g stall concept but before details I would like to remnnd Those speeds which I mentioned in my reply is described as Vs1g stall Speed in Old FCOMs
(editions of A 330 FCOM later than FEB 2017, does not contain those Vs1g stall speed charts, it can be found at the earlier editions)
Additionally the speeds like V2 etc is not based Vs1g (by regulation) but based on VSR (reference stall speed) and VSR cannot be less than 1-g stall speed as mentioned in CS25-103 and CS 25-107.

Yes in fact the speeds declared as Vs1g speeds are not real stall speed but practically at the edge of stall speed and they are considered as stall speed for certificate demonstration for protected (i.e FBW normal law) airplane. Example when a FBW airplane is tried to be flown with full Aft SS and idle engine (assume ALPHA FLOOR is deactivated for e.g AIRBUS), eventually airplane start to descent. But this descent is not a stall descent (no buffet or loss of pitch or roll control) but a 1g (constant vertical vertical speed) sink or descent. The speed throughout this descent is considered as Vs1g so this defined speed by applicant comply with VSR requirement as mentioned in CS-25-103.
However in a real Stalled unprotected airplane does not sink or descent with a constant vertical speed and 1g; a stalled airplane practically falls down with buffet and mostly with loss of control in pitch and roll. even yaw depending on model. In this case obviously the g on airplane will be less than 1g. Therefore the demonstrated stall speed will be even less than the stall speed where stall started due to reduced g (reduced apparent weight) and will not comply with CS25-103 requirements. To eliminate the stall speed concept differences between Protected and Unprotected airplane while calculating V2, Vref etc, by regulation (CS 25), rather than using Vs1g speed (for protected airplane) or Vs speed (for unprotected airplane), a VSR is used as compensating g effect by this equation (VSR= Vclmax/SQRT (Load Factor)) as mentioned in CS 25.103.

Last words. For Airbus FBW, since demonstrated V1sg complies with VSR (not bigger but equal) therefore speeds like V2 or Vref can be based on Vs1g. Therfore we can say as V2min = Vs1g x 1.13 or Vref= !.23 x Vs1g (for example in 25.107 V2min is defined as 1.13 x VSR)
These are well explained in FCOM CRECTERISTIC SPEED SECTION of AIRBUS, no idea about Boeing.

[FlightDetent]

Excellent work, JABBARA.

[Check Airman]

Since the 1g stall requires continual backstick I wonder if the aircraft would recover from a stall hands off if you did go from F3 to 1. The speed for F3 is lower, sure, but the critical angle is less too.

I imagine it would. In theory at least. The computers would recognise the new configuration, and respect the new AoA limit.