Is VLS kind of speed can't be violated in A320 family ?

[LegiossTypeH]

Hello all,

Here is the scenario in my check:
I get a ENG failed and shut down then shoot the approach. When close to to runway (below DA), I initiate go around due to some reason, Vapp=140kts, VLS=136kts,
after TOGA thrust and flaps one step up, the VLS=138kts, managed speed target= 140kts (same as Vapp), but my current speed drop to 132kts due to pitch up . Then he fails me because my speed below VLS.

My question is: Except stable approach criteria (company by company), is the VLS kind of speed cannot be violated ?
I don't find any description in FCOM about go around low speed limit, either in other phase like climb phase(I mean after acceleration altitude.), descent phase.
Yes above VLS is always safe side I know, and it is a threshold to activate Airbus's protections,
but, Airbus never say the VLS is a speed pilot's can't violate, doesn't it ?

Does anybody have documents about that ?

[Qwark]

I think the answer will not be with Airbus documents but with your operators checking manual or state legislation. They should describe handling tolerances for the check ride. Sustained flight below VLS when OEI would seem a reasonable reason to fail the assessment.Obviously difficult to say without the knowledge of the overall check performance.

[Uplinker]

Vls is the lowest speed you can select, but that does not prevent you flying slower manually.

However, there is no reason to fly below Vls, and your airline SOPs probably state somewhere that speeds below Vls are not allowed.

I found this from a previous airline’s documentation, (edited):

Handling​ errors ​
- Speed close​ to plus​ 20 ​
- Flight below​ VLS/Low​ energy ​

In your case, you state that the speed bug was at 140kts, but you got down to 132 kts. That is below the +10/-5 kts speed range that is normally allowed, so I suspect your fail was due to going below Vls and 5kts too slow.

Go-around pitch can be difficult to set in the heat of the moment; make sure you keep scanning and nail the pitch at +15° (or +12.5° on one engine).

[FlightDetent]

My understanding is that for OEI Vls strongly correlates with Vmca, the numbers can by distilled from the FCOM. Not observing the latter is a valid reason, I am afraid.

Moreover, the EASA rules clearly spell out the acceptable tolerances for a skill test. IIRC for V2 it is plus 10 and minus 0. Even under a different regulator, that is a strong guidance. +10/-5 kt for OEI, checked the books.

[LegiossTypeH]

My company has VLS limitation in stable approach criteria regulations, but not to mention in other flight phase like go-around.
I don't think it apply to go-around phase just because if my speed below VLS between DA and runway, like 50ft AAL, due to turbulence to typhoon, then I have to initial go around.
If I have the VLS limitation, does it mean I have to accelerate to VLS initially, with only one engine, then I can pitch up?

I thought about V2, too, but the logic of V2 is different from "manage speed target" in go-around phase, in Airbus A320 family, so it may not be the way the answer.

About the + or - 5kts, 10 degrees heading, 100ft altitude tolerance rule, I'm not sure it apply to approach or go around phase, the reason are as below:
1. Pilot never can fly 100ft below DA/MDA if no runway visual references.
2. Pilot can't fly a speed below VLS in final approach even it is within 5kts of Vapp.
3. 10 degrees heading... of course !
.... I guess this is why my check airman not to write down my "speed more than 5kts below manage speed target", but "Below VLS". He is serious in this reason.

We can presume the + or - 5kts tolerance rule apply to all circumstances, including my case, go-around phase, but that will be strange when over weight landing. Everyone knows we need to select VLS through FCU in final approach, that will about 5kts or more (depends how many system failures) below Vapp inserted. If you select flaps 3 for landing, after you initiate go around with TOGA thrust, you will not only be immediately far from VLS, but definitely more than 5kts below manage speed target(Vapp or VLS).

FCTM OVERWEIGHT LANDING CHAPTER:
"For a go-around, if the landing configuration is different from FLAP FULL, FLAP 1 must be used. If a go-around FLAP 1 is performed, VLS CONF 1+F may be higher than VLS CONF 3 +5kts. The recommendation in such a case is to follow SRS orders that accelerates the aircraft up to the displayed VLS."

That's why I ask the question:
Is VLS kind of speed can't be violated?
Or there are some exceptions? What are they?

I have a theory about go-around: Make a positive climb is the most important concern as long as speed not drop to V alpha prot. in Airbus or Vs0 in Boeing.
I don't find anything to support it, but find there's no description about low speed limitation when go around in airbus manuals.
(Only description of "manage speed target", which has a low limit Vapp, and a high limit VLS+15kts in One ENG OUT.)

Simply speaking: The "speed target", means the pilot needs to fly toward it, then maintains, not to mention pilot can't be too far initially. Like approach, we extend FLAP 1 at green dot + 10kts, then we inevitably far far from S speed initially. So as my case, how can I been blamed to be far from manage speed target initially?

Thanks for you all finish so many words.

[sonicbum]

Hello all,

Here is the scenario in my check:
I get a ENG failed and shut down then shoot the approach. When close to to runway (below DA), I initiate go around due to some reason, Vapp=140kts, VLS=136kts,
after TOGA thrust and flaps one step up, the VLS=138kts, managed speed target= 140kts (same as Vapp), but my current speed drop to 132kts due to pitch up . Then he fails me because my speed below VLS.

My question is: Except stable approach criteria (company by company), is the VLS kind of speed cannot be violated ?
I don't find any description in FCOM about go around low speed limit, either in other phase like climb phase(I mean after acceleration altitude.), descent phase.
Yes above VLS is always safe side I know, and it is a threshold to activate Airbus's protections,
but, Airbus never say the VLS is a speed pilot's can't violate, doesn't it ?

Does anybody have documents about that ?

Hi,
In landing configurations (CONF 3 and FULL) VLS is always equal to, or greater than, VMCL. (FCOM)
Hence flying below VLS could bring You below VMCL, ie. being unable to control the aircraft with asymmetric thrust.
It is a typical occurrence during LCP/OPCs as everybody tries to aim directly for the 12,5 degrees with a fast rotation rate and at medium/high weight it results in the speed dropping below vls. Rotate smoothly towards a 10 degrees pitch attitude and let your speed stabilize, then continue slightly up to 12.5 and from there follow the SRS.

[vilas]

There is Vapp and Vls, sometimes Vapp can be Vls. Permitted +10/-5 is to Vapp. Flying +15 can be called sloppy flying but below Vls is unsafe flying. Depending on some factors flying below Vls can trigger alpha protection, alpha floor etc. so unlikely to be forgiven. Except takeoff flying the FD will ensure everything if not available then fly the pitch.

[Check Airman]

For how long was your speed below Vls? Was there turbulence? If it was only momentary, and you immediately corrected, he may have been a bit harsh.

Vmc aside, the plane can safely be flown below Vls, but I’d say there needs to be a specific reason for it.

[vilas]

For how long was your speed below Vls? Was there turbulence? If it was only momentary, and you immediately corrected, he may have been a bit harsh.
Vmc aside, the plane can safely be flown below Vls, but I’d say there needs to be a specific reason for it. Where ever speed is to be reduced in select mode (slat/flap jam) Airbus mentions not below Vls. So other than turbulence where speed can fluctuate about Vls what could be the specific reasons to fly below Vls? Also what is the definition of safely? Getting into alpha prot with manual thrust trips the AP aircraft will be latched to the speed leading to descent or climb as per AoA is that safe?

[hikoushi]

I could obviously not second guess either your experience or the check airman’s judgment, having not been there but....

Generally Vls in the scenario you describe is treated as a sort of “caution range” before you start hitting protections. In other words, if you wind up there it will prompt you to very quickly get yourself out of whatever situation made you so slow in the first place. Basically being below Vls is a symptom of something else, whether turbulence / shear, or mishandling of some kind. The questions I would have would be:

How did you get below Vls? Rapid over-pitching? Mishandling thrust or rudder? Gusts?

How long were you there, how prompt were your corrections, and did you correct whatever originally caused the excursion?

The difference between an acceptable and unacceptable grade often has to do with how quickly you recognized the deviation, if you recognized what actually caused it in the first place, and importantly how timely and appropriate your correction was relative to the underlying cause (for example the pitch excursion that caused the speed to drop in the first place). It often also has to do with the “big picture” of the overall session, or the other aspects of the maneuver. Where there other issues that were close to the edges of the standard? Or was absolutely everything else perfect except for that one thing? Big picture context matters.

Somewhere your company has a standards document, which is likely based on and expanded from the ATPL test standards of your country. The company document should also contain specific guidelines for how to grade deviations from that standard. First thing I would do is ask to see this, and very, very honestly assess yourself based on what it says.

It is more important to see ourselves clearly than to be right all the time. Otherwise we lose the open mindedness to continue improving our own weak points, which we ALL have. I have been on both sides of your scenario, and let me tell you.... Ego has no place in this business. Yours will be bruised, just as much as mine has been! Your check airman has had his share, too.

[LegiossTypeH]

There is Vapp and Vls, sometimes Vapp can be Vls. Permitted +10/-5 is to Vapp. Flying +15 can be called sloppy flying but below Vls is unsafe flying. Depending on some factors flying below Vls can trigger alpha protection, alpha floor etc. so unlikely to be forgiven. Except takeoff flying the FD will ensure everything if not available then fly the pitch.
I am about 50AAL with manual flight and autothrust engaged, a plane cross hold-short line into runway seen by pilot not fly, then I initiate go around immediate by push to TOGA thrust (One Engine Only).
The FD command to pull up rapidly and I follow it, so speed drop a lot from 140kts to 132kts. I found it and pitch down, then the sim been frozen, and I am declared to fail the check due to below VLS, means I break the speed limit.

After go around, the managed speed target is 140kts=Vapp when go around initiated.
I check the manual, the VLS in CONF FULL with my weight is 136kts, after go around with flap one step up, the VLS is 138kts, same as what I see when the sim been frozen.
According FCOM limitation speed, VMCL=122kts, VCMA in CONF 3 is 130kts/ CONF FULL is 131kts.
I fought with the Check Airman so I know there are not any "go around low speed limit" description in my company's documents, none at all,
What he told to me is: "VLS is a lowest speed in any circumstances".
My company's target speed tolerance is plus and minus 10kts, not 5kts,
and the reason to fail me is NOT "Unsafe", "Danger to the plane" or something like that.
It is I VIOLATE THE SPEED LIMITATION. <- My question !

[Uplinker]

Just to remind us. From an A320 FCOM, (might be out of date):

VLS​ :​ Lowest Selectable Speed.​
Represented by the top of an amber strip along the airspeed scale on the PFD.​
Computed by the FAC, based on aerodynamic data, and corresponds to 1.13 VS during​
takeoff, or following a touch and go.​
Becomes 1.23 VS, after retraction of one step of flaps.​
Becomes 1.28 VS, when in clean configuration.​ (my bold). i.e. VLS is a certain margin above the computed stall speed, so not a speed you want to be below.


Interestingly:
Note:The AP/FD TCAS mode is speed protected, i.e. it ensures that the aircraft speed remains between VLS- 5 kt and Vmax.


@sonicbum, Nice tip on pitching up for go-around :ok: Wish I had thought of that myself.

[Check Airman]

Where ever speed is to be reduced in select mode (slat/flap jam) Airbus mentions not below Vls. So other than turbulence where speed can fluctuate about Vls what could be the specific reasons to fly below Vls? Also what is the definition of safely? Getting into alpha prot with manual thrust trips the AP aircraft will be latched to the speed leading to descent or climb as per AoA is that safe?

I was thinking in terms of terrain or windshear escape. You can safely fly below Vls (V a prot for that matter) to maximise the airplane’s performance. At Vls, you still have a healthy margin to Vs1g. Obviously on a normal GA, that would be inappropriate.

I only pointed that out because the OP asked if Vls was some inviolable speed.

[FlightDetent]

I do not think it is. This dot better stay connected though: Below 50t Vls(c=F) is limited by Vmc(L), if I am reading the FCOM right.

The original answer can be answered in positive as well: Since normal Vapp is Vls+5 and limiting accuracy on a test is -5, the Vls marks the inviolable zone anyway.

[OPEN DES]

off-topic:
the appr corr of 5kt which the fmgs takes as a minimum assumes the use of A/THR. Nothing that stops you from flying Vapp=Vls when man thr. In case of failure when delta vref more than 15 or 20, there is no appr corr anyway. And Vapp will sit right on Vls. How about flying -5/+10kt then? Not a ‘violation’ in my book, sloppy flying yes....

on-topic:
as always: a test is subjective. No way to say whether you were passable or not without being there. A quick drop below Vls when timely recognized and corrected would not be a fail.......

[vilas]

From Airbus document
Vls is
• Lowest selectable speed
• Represents minimum regulatory speeds depending on flight phase (can be VMCA, VMCL or Vs1g limited)
• Provides appropriate margin versus buffet at high
altitude
• Provides appropriate bank angle maneuverability
(defined by regulation) in a stabilised turn.
​​​​​​_________________________________________________ __
My inputs
Obviously when Vls is target speed it will fluctuate between a little less and more. But it is not a speed for sustained flight. At Vls Regulation requires to have 40° bank manoeuvrability and Airbus has it. At Vls, 40° bank in stabilised turn triggers alpha floor.
When one may procedurally land up flying temporarily below Vls is during overweight approach in flap3 and Go around with flap1. At that instant the speed could be below Vls 1+F. But it still is above regulatory requirement.

[LegiossTypeH]

Thanks for you all give me so many information and opinions,
so may I conclude as below ?

1. VLS is not a limitation nor a speed pilot always have to be at or above, but only a lowest selectable speed for autothrust.
2. Pilot can fly a speed below VLS momentarily with a good reason. It is a common sense, or check/test standard in most company, not words in FCOM or FCTM.
3. VLS is a speed with sufficient margin to stall or activate Airbus protection.
4. In a check/test, normally speed tolerance is +10kts/-5kts.

That's what and why I answered when he asked how do I feel :
I confess I'm not flying good, but I don't violate anything, and I'm still in a positive climb, which is the most important while in such low altitude with a plane get into the runway. I don't understand why I should wait until the power comes up just to maintain a speed at or above VLS, or the manage speed target. It is a high bypass ratio Engine.

[FlightDetent]

And so you have been rightfully failed. Not because of insufficient piloting finesse, but rather for lack of understanding why speed control is relevant, and inability to accept own mistakes. The last one, together with ignorance of why Vmca just might be important on a OEI G/A may cause you trouble next time too, be aware.

[LegiossTypeH]

And so you have been rightfully failed. Not because of insufficient piloting finesse, but rather for lack of understanding why speed control is relevant, and inability to accept own mistakes. The last one, together with ignorance of why Vmca just might be important on a OEI G/A may cause you trouble next time too, be aware.

Sir, all the V speed are already in #11 and #12.

[LegiossTypeH]

I find some more words in my FCOM PERFORMANCE Chapter, as below:

REFERENCE SPEED (VREF)
VREF is equal to the VLS of CONF FULL. VREF is used to determine the Final Approach Speed (VAPP) when a system failure affects the landing performance.

GO-AROUND SPEED
In the case of a missed approach, the go-around climb gradient is calculated at the go-around speed.
The standard go-around speed is 1.23 VS1G of the go-around configuration. For approaches with a decision height at or above 200 ft, where approach climb performance is found restrictive, the go-around speed can be increase up to 1.3 VS1G of the go-around configuration.

[Todd Rich]

This is one of the finer points in understanding the Airbus. VLS is the lowest selectable speed (non-managed auto-thrust engaged). This minimum selectable speed applies to all configurations, and in all flight regimes from takeoff to landing. It is important to point out that lowest selectable is to be distinguished from lowest flyable. speed. This distinction is worth noting because it is possible for the aircraft to fly below VLS, even while VLS is selected. For example, turbulence, or a sudden pitch change up. There is no ability to select below VLS unless the auto-thrust is turned off. The Airbus engineers knew that it is possible for the aircraft to find itself below VLS, but at the same time that possibility is engineered into the jet, and the auto-thrust will be working to get itself back above VLS the moment it goes below VLS. The smart Airbus pilot knows that the safe envelope of this jet is to be able to select down to VLS. And the smart Airbus pilot knows that this is a perfectly safe speed. You might have noticed that VLS up at cruise altitude is somewhere around 40 knots above Alpha Max (top of red zipper), and Alpha Max represents 1.1Vstall. With that said there is no good reason I can think of up at cruise altitude to fly the aircraft below Green Dot because once the aircraft slows below Green Dot, the jet is below L/D Max, and that would result in more fuel burn. Holding speed should always be at L/D Max for that very reason, and that's the reason why Managed holding speed is always Green Dot. Green Dot give the maximum endurance fuel burn, and that's exactly what a pilot wants in a holding pattern. I am surprised sometimes that experienced pilots will think that it's good airmanship to add speed to Green Dot in a holding pattern. Doing that only increases fuel burn. There is a tremendous amount of stall margin on an Airbus at Green Dot, so that's where you want to be when max endurance is the goal. Holding is exactly that situation.

It is also important to point out that the lowest selectable speed managed and clean is Green Dot, after that, the characteristic speeds are the minimum speeds as the aircraft is configured. In selected mode, however, it is always VLS that is your lowest selectable speed, and that is important to understand. For example, if one finds themselves in a radar pattern at a congested airport, and perhaps you might be on a 25NM downwind at 5,000 feet. The controller asks you to slow to 190. The smart Airbus pilot will look at the VLS, and as long as 190 is above VLS, he will not go to Flaps 1. He will realize the jet is fully maneuverable down to VLS in any configuration, and as such, will fly the jet clean at 190 knots. That's smart because it saves fuel, and again, in no way safety is compromised. To the contrary, safety is enhanced because fuel is being saved that might be needed in the case of a longer delay and a diversion. This issue especially holds true when going from Flaps 1 to Flaps 2 because the amount of increased drag going from Flaps 1 to 2 is quite significant. So if on that same 25 mile downwind, ATC slows you to 170, you want to stay at Flaps 1, even if the nose is a little high. As long as the jet is above VLS, you are safe and solidly in the envelope, and you are saving fuel - a lot of fuel.

Bottom line, understanding the lowest selectable speed is VLS is a safe speed and a smart speed in certain cases, will make you a much better Airbus pilot.

[FlightDetent]

Have you tried going around from CONF 1 at 170 kts recently?

[FullWings]

Thanks for you all give me so many information and opinions,
so may I conclude as below ?

1. VLS is not a limitation nor a speed pilot always have to be at or above, but only a lowest selectable speed for autothrust.
2. Pilot can fly a speed below VLS momentarily with a good reason. It is a common sense, or check/test standard in most company, not words in FCOM or FCTM.
3. VLS is a speed with sufficient margin to stall or activate Airbus protection.
4. In a check/test, normally speed tolerance is +10kts/-5kts.

That's what and why I answered when he asked how do I feel :
I confess I'm not flying good, but I don't violate anything, and I'm still in a positive climb, which is the most important while in such low altitude with a plane get into the runway. I don't understand why I should wait until the power comes up just to maintain a speed at or above VLS, or the manage speed target. It is a high bypass ratio Engine.
I’m not Airbus qualified but I think most TREs assess in a similar manner whatever aircraft is involved.

If you’re uneasy with someone’s general standard of operation under check, and you think they need more training and/or to come in on another day as there may be external factors that are influencing their performance, then a point where formal test parameters are breached is somewhere to “hang your hat” on the paperwork. It may have been a debrief item otherwise, or you were exemplary elsewhere but had a picky trainer. Self-analysing, what do you think, and what will you do differently to pass your next detail with flying colours?

[vilas]

In a test overall performance is considered. Perhaps dropping speed below VLS was the last straw. Flying below VLS is a minus if alongwith some other minuses can result in a failure. Instead of trying to find justification if you can find why it happened and how you planned to avoid next time will be productive.

[FlightDetent]

It's been 3 years since the OP opened the thread, surely he's moved to a higher level by now.

[pineteam]

in my outfit: For the PPC, we have a tolerance of +-10kt on the speed for single engine go around. A momentary drop below the target speed (limited to 10 Kts) is acceptable during go around phase.

[Todd Rich]

I assume you mean ATC tells you to go around on final, and you're configured to Config 1, and doing 170? That scenario would be unusual in that it is a requirement, at least at our operation, to be fully configured by 1,000' agl. So if I were at 170, and in Config 1, that would have to be happening a good ways out on final, or maybe on some kind of extended vector where ATC was asking me to do 170 knots. But if your question is rhetorical in the sense that your suggesting that a go-around from Config 1 is unsafe, consider that if ATC asked you to abort the approach, and you were at 170 knots config one, that would not be the same type go around as text book one done, fully configured and down near the ground. That would be a smooth application of power without pitching the nose way up. In effect, not really a go-around, in any case, very safe, very normal - unless the pilot made it unsafe by ripping the nose up. But why would he or she do that? So that scenario of going around from 170, Config 1 needs to be explained in more detail for me to visualize what you are visualizing.

[rexarus]

I would also point out that Green Dot and VLS are often the same speed up at cruise altitude. So that means managed holding would be at VLS in those cases.

[vilas]

I would also point out that Green Dot and VLS are often the same speed up at cruise altitude. So that means managed holding would be at VLS in those cases.
At cruise altitude you can't hold at VLS because during a turn Valpha prot will rise and trip the AP. Higher levels ICAO holding speeds are Like M.8 or above 340 it's.83.

[Romasik]

No. It can be violated. It cannot be selected. You can legally fly at VLS and it may momentarily go below due to aerodynamic or weather conditions. You should not intentionally fly below VLS and if you miss it and didn't correct, then it may be a failure point.