A320 S speed question
 

Once I was flying the 320 on a terminal are, and were requested to slow down. So I asked for F1, what led the airplane to fly at S speed, around 182kt. The APP requested the speed to be reduced to 170kt, so, as we were far from the airport, and I did not want the airplane to fly with the flaps out, I manually selected the speed at 170, thus flying below the S speed. I did so because I understood that the minimum speed I could fly in would be VLS, as, the name says, is the Lowest Selectable speed. The captn of the flight told me I was wrong, and should never have done it. That I could not fly below S speed, and, instead, had to ask for F2 and fly above F speed. Does he have a valid point ?

He sort of has a point. You can fly below S speed, as u demonstrated, but from an operational point of view, I agree that u probably should have extended flaps, although I can see ur point for wanting to keep them in.

Green dot, S and F are maneuvering speeds in the selected config. So although the plane can safely be flown below the speeds in that config, you may not have adequete protection against stall for all the maneuvers that the plane is certified for. It's highly unlikely that you will have to push the plane to the edge of the envelope like that in a terminal though. He should have said that u SHOULD not fly below S speed.

VLS is the lowest speed that the autothrust will maintain. You can fly below this speed in manual flight.

FCOM 3.4.10 P2 defines 'S' speed as:

Minimum speed at which the slats may be retracted at takeoff.
In approach, used as a target speed when the aircraft is in CONF 1.
Represented by "S" on the PFD airspeed scale.
Equal to about 1.23 VS of clean configuration.

I'd go along with Check Airman's spin on it - not a good idea.

Cheers,
mcdhu

The operating policy in my company (BA), is to 'give consideration' to selecting flap 2 when atc request a speed between S speed and Vls on the approach.

I personally prefer this approach, ie to leave it to the pilot 'on the day'.

I think it depends on the prevailing conditions and flight profile.

Personal reasons for taking flap 2:
- above the glideslope (goes down better with F2)
- in icing (incr thrust with TAI on)
- in turbulence (better margins)
- if more than about 15kts below S-Speed

Personal reasons for sticking at flap 1:
- smooth air conditions
- more than 8nm to touchdown and below glideslope.

Just my thoughts....

I agree guys/gals - normally one would extend some flap when slowing below S speed but you don't HAVE to.
There has been a couple of times I've used selected speed below S in Conf 1 following an ATC request - but only for a max of S - 10 knots and whilst flying a longish period of straight and level . Also told my F/O why and ensured he/she was aware & happy.

Thanks for all the postings. Whatchdog, what hapenned with me was exactly what hapenned to you. I did not want to fly far and low having flaps down. The thought of this S speed makes me think about another thing.

Let´s say I want to make a close in turn, and select on PERF v2+10 or +20, so I can climb faster and have a minimum turn ratio. Then we would have the aircraft flying close to the ground, still with a speed under S. Would that be something wrong to do ?

complicating things
 

Eisenhower:

Don´t try to find it in FCOM and certainly dont try it out with "that" Cpt, but how about setting Flaps 2 and back to Flap 1 so u get your flaps in 1 position (to-ff position) ?
I am not sure what might happen to S speed, probably it will remain the same, as S,F speed are computed according to flap lever position but certainly VLS will go down as it reflects the high-lift devices actual position.

Anyway, I wouldnt do it for procedure sake.
Just an option to consider, probably widely discussed and dismissed by the Airbus engineers.

Saludos
LUPA

Green Dot / 'S' / 'F' partially represent the Min Drag speeds. Flying with F1 below S is "legal" in most people's books (as stated above) but not very sensible or good airmanship. Drag & Fuel Consumption will increase over the F2 situation, you are the wrong side of the "Drag Curve", you have less "buffer" from minimum speeds e.g. in the case of turbulence / wake, and apart from anything else, have an uncomfortably high nose attitude to maintain level flight....
Personally, if my P2 tries to fly anything more than a couple of knots below S with F1, I try to gently suggest F2 might be a nice idea :)
Just my 2ps worth ;)
NoD

I like this idea better tham my own. The environment in which we work is too dynamic for hard and fast rules written in stone. Assess the situation, then take appropriate action. It could be that 99% of the time, one procedure works fine, but we're paid to use judgement and call upon our experience as professionals.

Thanks to everyone who posted their opinions.

LUPA, I could not do what you said, for 2 reasons:

1) It would give me a trailing edge flap, something I did not want to in order to avoid drag.

2) all acft are equipped with FOQA, what would make me and the captn go for some coffee and biscuits.

What's FOQA?

Looking at the original situation from a different angle, is there anything wrong with asking ATC if 180 kts, or whatever your S speed is, is OK? They are well aware that we are trying to fly as efficiently as possible to avoid making too much noise or burning too much fuel. Don't ask, don't get?
Question for ATC - would this be too much of a pain, assuming it isn't obvious you are working flat out at rush hour and the airwaves are full. Will you accept any leeway on speed without us asking, say 5 - 10 kts, if it allows us to keep a cleaner configuration for a bit longer, ?

I believe the limit is +or-10kts anyway.

Yep, + or - 10kt is Ok, but since there was an acft some 6nm ahead, I decided to slow down in order to allow separation.

FOQA- Flight Operations Quality Assurance. A device installed that copies info from the data recorders and compares with given values. Depending on the discrepancy, you will be called for a cup of tea.

No Airline's Flight Data Monitoring program ought to pick up pilots for operating well within the aircraft envelope, as in the situation LUPA describes...just because on a 'normal' line flight we only move the flaps in one direction after we have cleaned up post-takeoff, doesn't mean that we can't! What if ATC changed their minds and asked for green dot speed (220kts?) again, after requesting 180? Would you expect FOQA to pick up on that if no limit speeds we exceeded on minimum speeds underflown?

I would expect not - b*llocking pilots who don't fly 'just so' is not what FOQA does - speak to your Flight Safety department about the system and learn about the benefits for all of us, rather than subscribe to the usual uninformed crewroom urban myths about FDM!

Now, the kind of thing FOQA may be set up to spot, is deliberately flying below manoeuvre speeds for the current configuration...that should result in a quick Q&A with the boss!

LUPA's idea might be worth trying one day, with a well-briefed crew and (ideally) a low workload situation (just so you are more able to monitor things properly!).

Well, Gary, this F2 to F1 selection was discussed during the Ground School refreshment, and it was told us that FOQA had been programmed to show if that maneuver happens. I am not going to be the one going for a cup of tea, even thinking like you, that maneuvers that are on the operating limits shouldn´t be repressed. But, I am the employee, not the employer.

I say cooperate and graduate, yes you can safely operate below the S speed but the majority of operators do not operate like this, your cpt is giving you correct information.

From A320 Instructor Support Manual- ' You may fly below current maneuvring speed of the current configuration, provided you fly above VLS '.
Of course you can fly below S speed with Flap One out!

What do you do in case of a flapless or slatless approach, reference maneuvring speed? You fly below your maneuvring speed but > VLS.

But when you are told to fly 180kts by ATC, for example, and S speed is 185kts, most punters will happily fly high drag with flap 2. :\

Personally, I don't do it. The concept is poorly understood by A320 pilots. And seeing an aviator turning blue, because you are a few knots below S speed, ain't worth the hassle!

Fair enough, Eisey - the culture in my company re: FOQA/SESMA/OPTIC/whatever you call it does not result in cups of tea very often, unless it is very obvious that negligence is a factor. Instead it is used to identify operating trends (such as pilots flying below S speed etc) and permit safety management to either a) write a fleet memo saying DO or DON'T and/or b) change SOPs accordingly and hopefully also c) allow the training department to conduct proper training/explanation of the circumstances.

Individual pilots should not to be pulled out of the ranks unless something warrants serious re-training. If that is unfortunately the culture where you work, I am sorry.

Still doesn't change my suspicion that if the FOQA picks up when F1 is reselected after F2 extension, it would almost certainly pick up flying below S speed with only F1 selected, regardless of the rights and wrongs discussed here, since whilst still within the operational envelope (as agreed here) it falls outside most companies (and so I suspect also the manufacturer's) SOPs for airmanship reasons.


So if you really want to avoid a 'cup of tea', the (somewhat flippant but still valid) response has to be:

1) stick to your company SOPs, even when you think you have a 'better' idea
2) if your fellow crewmember (Captain OR First Officer) is unhappy with the reasoning behind a proposed deviation from SOP, you have a duty to keep them 'in the loop' and comfortable with the operation; so resist trying it on this occasion! In any case see rule 1)
3) Take your suggestion to your technical pilot/chief training captain for the definitive response and (if necessary) top cover - you might be thanked for it, or you might learn something.

This issue seems broadly split on technical validity, but ought to be considered also from airmanship and CRM terms, as mentioned.

All the best,
GL

From the Airbus Instructors Support Manual- "You may fly below current maneuvring speed of the configuration, provided speed is above VLS".
I would suggest this means flying below S speed is OK. But typical Airbus, have yet to, incredulously considering the price of oil, incorporated this into FCOM.

At max landing weight, your flaps jam. S speed is 182kts. Vref is 134kts. Approach increment is 25kts. Your Vapp is now 159kts. You can suffer an engine failure in this scenario and still have no restrictions flying below S speed without Flap 2!

That Airbus pilots are uncomfortable flying a few knots below S speed, is testament of how much the French are dumming down this profession.
Flying a level segment, with high drag Flap Two, burning an extra 20kg a minute, to meet an ATC speed requirement is poor airmanship IMHO.

I am confident Airbus will incorporate the practice of flying below S speed without Flap 2, when the price of oil makes 'green' approaches all the fuss.

OK - I stand corrected; it's been a few years since I least flew one, but the requirement to use S spd as a min with F1 only was then my company (large UK airbus operator) SOP.

Yes, as I mentioned, most operators operate the same way.:rolleyes:

You're getting to caught up in this. The Aircraft will fly at Flaps 1 right up to Alpha Prot. The slower below S-speed, the less protection you have.

The FMGC displays S as the speed with config flaps 1 to give you a limit protection speed. You can go below it, right up to Alpha Prot, but you give up a lot of safety doing that. Not a big thing to go S minus 5 kts at config flaps 1, but why do it, what do you gain from that? Lot of variables there to consider, but balance them with the protection the FMGC is trying to provide you.

As for the pic TURNING BLUE, who's in charge there. You'll get your turn some day, respect the wishes of the guy or gal in the left seat(as well as the FMGC) and play it safe. Few knots isn't a big thing here. It's the concept of what you are trying to accomplish here.,

From the FCOM;

S Speed
Minimum speed at which the slats may be retracted at takeoff.
In approach, used as a target speed when the aircraft is in CONF 1.
Represented by "S" on the PFD airspeed scale.
Equal to about 1.23 VS of clean configuration.


The FAC computes :
-The minimum and maximum speeds :
-VSW (stall warning)
-VLS
-VFE and VFE for the next configuration
-VLE
-VMO/MMO

The maneuvering speeds :
-Green Dot Speed
-S speed
-F speed

So, the way I read it, it isn’t the FMGC – it’s the FAC that computes and displays on the speedtape (and the speedtape speeds can (and often do) differ slightly from the FMGC Appr page) and thatGreen Dot, F and S are not protection speeds but target manoeuvring speeds.

Personally I cannot see the point of flying below the calculated manoeuvre speed.

Quite right, there is no point, I believe it's another case of a new airbus guy trying to reinvent the wheel (the captain doesen't understand the airplane), thinks it's in the interest of saving what I don't know, with the deck angle in that configuration I would bet it's cheaper to be at CON FIG 2 never mind the comfort level for pax and crew.:rolleyes:

You should voice your concerns to Airbus, not new crew!

Rehashing, it is Airbus that is teaching it's Instructor Pilots to impart the acceptability of flying below S speed in Config 1.

Comfort? Not noticable.

Economy? About 20kg a minute cheaper, in a level segment @ Flap 1 a few knots below S speed, as opposed to Flap 2.

Safety? Normal Law with all protections. And you can fly on one engine, slats 1 only, no flap, above max landing weight, comfortably, with an approach speed of VLS Config Full plus 25KTS.

Let's not mix good professional debate with unfounded, personal sentiments.

Well writen, Gnadenburg. Surelly makes clear who does not understand neither the things that are happening around, nor the protections given.

No one is trying to reinvent the wheel. It is just people who fly and UNDERSTAND the airplane that are talking over concepts and information that someone who flies the machine should have. This makes the difference between pilots and drivers.

If one does not understand what is going around, he/she should not show how stupid they are, right, Dream Land ?

No problem to fly below S speed.

The only reason that the bus doesn't slow below S speed when speed is managed is so that you can retract the slats and still be managed. S speed is the min speed to retract flaps slats to 0 that is it.
Min maneuver speed for the existing weight and configuration is shown by VLS

As far as going to 2 and back to 1. Airbus discourages this and although it does lower the nose of the airplane it increases the fuel burn.

Eisenhower, your cpt may have misspoken by saying you can't do it, there is no operational limitation as mentioned in the first post, this is an simply an operating technique taught by Airbus for our airline.

well well, what has racism, ostracism or briticism to do with S speed Gnadenburg?
 

Just hope that all the well apreciated European and world wide engineers working for airbus along French colleagues do not share your inappropriate and degrading remark about French which is irrespectufull for the French nationals working for Airbus!

Thought the middle age was over, even in the farm land of Eden Valley.

There are a lot of personal definitions coming out here.
S speed is the manoeuvring speed at F1 (not config 1 as per take off accel!).
Deliberately flying below manoeuvring speed is poor airmanship (even if VLS/ATHR is there as a back up to look after you!).
You may be planning a straight course, speed reduction but sometimes you have to unexpectedly manoeuvre..................................hence manoeuvre speed!
This is nothing to do with France or indeed the Airbus but is valid for every tye I have flown (more than a few!).

And personal professional sentiments without qualification! Including yours!

Ad nauseum was my referrence to Airbus Instructor documentation that states an acceptability at flying below S speed with Config 1 selected, provided speed>VLS.

It has also been recently documented in the Airbus Flight Crew Training Manual.

So take it up with Airbus.

wheresthecoffee, you mention personal definitions and then (I think) you introduce one yourself
Where in FCOM does it talk about manoeuvre speeds? What is the reference? From your earlier post:-
At S speed after takeoff, you retract the flaps so by definition it must be safe to fly clean at S speed. In fact, S speed corresponds pretty much to VLS clean.
S speed is the target speed in CONF 1 but I don’t recall Airbus using the term ‘manoeuvre speed’. I think that is Boeing terminology. I have not flown the Airbus family for four years now but that was one of the big differences going for Airbus to Boeing. On the A320, perfectly acceptable to go below the target speed with a minimum of VLS; on a Boeing, you want to go below manoeuvre speed, it’s the next stage of flap (although even my Boeing manual says you have full manoevre capability at 20kt below manoevre speed!)

Of course, all this may have changed since I left but I was always taught that VLS meant exactly that, lowest selectable speed for that particular config.

If you can find anything in official Airbus documentation that says otherwise, I stand to be corrected.

FCOM 1.22.40 Flight Envelope

quote verbatim:

The maneuvering speeds :

* Green Dot Speed
* S speed
* F speed

unquote

When you take off with config 1, you don't have the same flap/slat configuration as you do when you select flap 1 on approach - maybe there lies the difference!

When your flaps lock on approach, are there any manouevre restrictions stated by Airbus? If your engine is lost in the same scenario, are there any manouevre restrictions? Remembering, Flaps locked means you will be flying below S speed without flap!

Incidently, single engine Flight Director restrictions on departure, are related directly to net climb gradients, and not an flight envelope limit.

Airbus " Flying below manuevre( sic ) speed for the configuration is acceptable, provided speed is greater than VLS ".

Mentioned in two Airbus manuals 1) Instructor Support 2) Flight Crew Training Manual. Both with reference to the approach scenario of ATC asking you to maintain speed a few knots below 'S'.

Gnad.....have you ever been at F1......REQUESTED.....F2,and as the flaps start to move,as seen on the ecam...gone back to F1.....this was an original procedure from Airbus.....most companys dont do it because of flap track wear........my point here is that will put the aircraft ia a better config at "s" at low speeds........

FOQA....is pilot friendly,we use it as a training tool,mostly for unstable apps ,but it cannot be used for enforcement action...not a big deal really,great training aid in groundschool....

Not familar with this procedure. Can you elaborate?

I have been at Flap One and > 200kts, Selected Flap Two, only to reselect Flap One. Not for your reasons but due an impending overspeed!
:ouch:

Thanks for the quote and I stand corrected. Hovever, I still stand by my original post in that you can retract to clean at S speed (which is defined as 1.23 Vstall clean) so the 1+F/1 debate isn't really relevant. VLS clean is the same as S speed.

I spent many years on the A320 from when it first came into service and did a manufacturers course all those years ago. We were definitely taught that coming back to VLS is OK. I think that, over the years, the original Airbus concept of flying anywhere between VLS and VMAX in whatever config you happen to be in has been diluted by successive generations of ex-Boeing pilots who have got used to doing it the other way. I must say that converting onto my current Boeing, I found it hard to understand why you couldn't come back to min manoeuvring speed (which, I would imagine, is the minimum speed you can manoeuvre at). As I said above, my Boeing manual says you have full manoeuve capability at 20kt below the manoeuvre speed.

What I am sure about is it is perfectly OK to go a few kt below S speed while at F1, unlike on my Boeing which does not allow it.

This is one of those circular debates without end so I'll say my last piece.

I can fly an aircraft just above the stall and, as long as no 'upset' occurs, all will be well.

So, by the same token, I can fly an airbus below the manufacturer's manoeuvre speed (which they also refer to as the 'target' speed for that configuration) and all will be well.

However, are either of the above examples of good airmanship............I don't think so!

Vls is a protection that exists when the A'Thr is engaged.........nothing else.

Manoeuver speeds are designed to give a margin of safety for manoeuvre in certain configs (hence the boeing -20 kts thing.............that's the margin).

Flying below that speed reduces the margin and negates the point of it being there in the first place.

Gnad....I should have been more specific.......10-12 yrs ago we used the procedure.....Flaps 1 +f....used at geen dot on long finals so as not to use Flaps 2 ,because of pitch attitude and drag.......the procedure(for us) is not prohibited but not reccommended due to flap track wear.....

Impending overspeeds.as you suggested, requires you to reduce flap settings at any config that goes into the "red"(auto thrust,auto pilot off,speed brakes,etc etc)......that is an action,not a procedure.

We used this as procedure,and to this day works very well.I would totaly agree with wheresthecoffee,Airbus wants these A/C flown on profile,within the "laws" of the A/C for which it is designed......only problem with that is ,as humans we tend to cock-up profiles and flying these things as designed{guilty as charged) .....there are many safe and efficent ways of flying "outside of the box" ....PB