F, S, green dot speeds

[pensador]

Many our instructors say that it is prohibited to fly on speeds less than F, S, green dot. I actually didnt find any place when it is written. Any thoughts?
Con respecto

[CaptainProp]

Basically these speed gives you protection in turns (g loads) as they are dynamic speeds dependent on weight etc. There is nothing really prohibiting you from flying below these speeds, with wings level at least. Remember, you are still protected by Vls, Alpha prot. etc. When having gusty conditions with max flap speeds close to min managed speed (f, s, green dot) I regularly select a speed below these speeds and allow the speed "fall" below before selecting flaps, this to protect myself from flap over speeds. Otherwise you will have the auto thrust adding thrust as soon as you get close to your minimum managed speed and it can sometimes be difficult to get the flaps out with a comfortable margin on the speed.

I have heard the same arguments before and I am sure we will see them here as well! :}

CP

[rudderrudderrat]

Hi Pensador,

I agree with CP - there is a clue in the FCTM page A027 P1/2.

"In the QRH, the line, "SPEED SEL............VFE NEXT -5 kt" is designed to allow the crew to configure the aircraft for landing whilst controlling the speed in a safe manner. This procedure may involve reducing speed below the manoeuvring speed for the current configuration which is acceptable provided the speed is kept above VLS. The speed reduction and configuration changes should preferably be carried out wings level."

[Nubboy]

On our fleet we regularly fly below F or S speed, and quite often turn as well. In fact do it most flights from ground level up to acceleration alt:ok:

[Dan Winterland]

Technicly - and obviously, you are safe down to VLS. F or S indicates the speed at which you will be safe to raise the flaps or slats with no danger of VLS coming up to meet or even overtake your current speed. In most cases, VLS comes no where near F or S, but try a heavyweight departure out of a 6000' elevation airfield at ISA+20 retracting in the turn and in turbulence. One of our destinations is often like this - there's a fair amont of "Pucker Factor" involved as VLS shoots up to meet you!

[pensador]

thanks everybody for your comments! As fo me F and S speeds, in addition, designe for the wrong flaps leaver moovement. Another words this is additional margine in case of mistaken flap retraction.
Con respecto!

[Dan Winterland]

Not always. An A330 departing from a challenging airport where flaps were selected to zero at about 15,000' a few knots too slow hit turbulence and entered Alpha Floor. Sometimes there is no margin.

[Feather Boa]

Dan

Retract the flaps after the turn is complete.

Saves the puckering!

Fx

[springbok449]

May I ask why you would deliberately fly below F, S and Green Dot speeds in selected speed?

Managed speed does not do it, so why take away the protection, all it needs is a distraction (ATC, Cabin...) or some turbulence to find yourself close to VLS and possibly triggering Alpha Floor shortly followed by tea and biscuits in the fleet office to explain your actions...

As stated above saves the puckering...

[Airbus_a321]

well said, springbok. No need at any time to go selected below the mentioned speeds....if you wanna go below, select next flaps..any other way is unprofessional

[CaptainProp]

Really? So if you are far out from the field (coming in for landing) and ATC requests a speed 10kts or so below your managed speed, you would consider it "unprofessional" to select the speed and keep the aircraft in clean config? I would say that it is perhaps not "unprofessional" but at least uneconomical to select flaps too far out unless necessary. Having said that, if my colleague is new-ish on type or just does not feel comfortable with it then there is no discussion - ask for the flaps. Personally I would tend not to though, however its not a competition.

Keep it safe, know the aircraft's abilities and limitations and more importantly - Know your own abilities and limitations.

CP

[Right Way Up]

CP

Out of interest do you know what is more economical flap 1 at S speed or flap 0 at green dot -10. My gut feeling would be that they are not that far different.

I'm surprised no ones mentioned selecting flap 2 then back to 1 on approach! ;)

[CaptainProp]

No, difficult to find any exact figures, but I am sure there are people smarter than me that made the calculations and that there is substance behind our recommended procedures asking for delayed flap selections "when possible", flap 3 landings etc etc.

It sometimes surprises me though when I hear from people that you cannot/are prohibited from flying below these speeds with current configuration. That to me shows that perhaps people are not always aware of what these speeds mean and how flying above or below them effects your aircraft and the protections.

But like I said earlier, its not a competition so fly in a way that is comfortable to you and the guy next to you.

[Nubboy]

Interesting points and all good stuff.

To re-iterate the original question, exactly where is it written that you shall not operate below these magic speeds. They are extremely useful, and as others have wriiten, give a very good clue as to how hard the wing is working, and what sort of margins you have left before things would become very interesting.

HOWEVER, top of the amber on the airbus is VLS, which is the lowest selectable speed avaible to the crew, AT THAT CONFIGURATION. Bumbling around northern europe at relatively modest weights,in an A319, there's normally a huge spread between any one of the early markers, green dot or F speed for config 1 or 2 especially, and VLS.

If fifi the wonderjet shows us exactly what that speed is, why can't we use it?
Airlines or manufactures?

Intrigued:confused:

[Dan Winterland]

Feather Boa.

''Dan

Retract the flaps after the turn is complete.

Saves the puckering!''

Thanks for the advice, but not an option at this airfield situated in a valley with an MSA of 20,800'. The grid MORA is over FL300. one of our more challenging destinations!

Judging from your username, I suspect you may know where this is.

[springbok449]

Interesting debate...

So what are the margins and limitations then, how far below F, S or green dot would you go before selecting the next Flap setting? 5Kts, 10Kts? Could someone please provide me with a reference.

I fully appreciate that you are protected but it does not mean that you have to explore the boundaries as I said earlier what if there is a distraction or something?

CP, referring to your first post, I dont know which family Airbuses you operate but in my experience on landing you are never close to an overspeed when you are approaching S, F or green dot, unless you are close to MLW or doing an overweight landing which would only occur if you have just dumped fuel and/or in an emergency...

As Nubboy says if the jet shows you the speed why not use it...?

For sure if ATC ask me to maintain 210Kts at 30 miles and green dot is 213Kts common sense would prevail, you either fly clean at 213Kts or clean at 210Kts...

Thks for the good info

[Slasher]

...there's a fair amont of "Pucker Factor" involved as VLS shoots up to meet you!

Whats the bloodey panic about VLS?

You can be anywhere within the hollow yellow bar as its ABOVE the speeds
where protections, bells and wistles activate. Its when your ASI enters all that
red and white crap under it that might cause you to have to think about whats
going on.

[Nubboy]

Slasher, I'm not panicing, just curious.

Why can I climb, managed, below F speed all day long if I want, but not use any of the green bit between VLS and the index for the current config in the descent or cruise?

Interestingly no one has mentioned the question of speed stability, unless I've missed it.

[CaptainProp]

As Nubboy says if the jet shows you the speed why not use it...?

Yes Springbok, but if you read again, to me it looks like Nubboy meant - Since the aircraft shows you Vls as a dynamic minimum speed then why not use the full range of speeds should you require or wish to do so? That's how I understand his point. Either way, this is my take on it.

[rudderrudderrat]

@ nubboy + Captain Prop,

Are you really asking why we don't routinely fly at a speeds below 130% V stall? (or whatever the margin is that Airbus has deemed appropriate)

[DesiPilot]

The Airbus Instructor support handbook I have clearly says this in Intermediate approach section
You may fly BELOW the maneuvering speed of the current configuration, provided you fly ABOVE VLS.

If I am given a speed to fly by ATC whch happens to be below O F S speed I just querry ATC and ask them if it is ok to fly O F S speed. In most cases they have no problem.

Do not forget along with alpha floor we also have alpha lock in case you retract the flaps below S F speeds.

[CaptainProp]

Rudderrudderrat - No, not "routinely" where on earth did you get that from?! The whole idea is that Airbus has provided us with a dynamic speed showing us exactly what you are saying, a margin that they have deemed "appropriate". So I am talking about possible and SAFE options that are available to you as a pilot.

The FCOM states -

"Minimum Selectable Speed (VLS):
The top of the amber strip along the speed scale indicates this speed. It indicates the lowest selectable speed providing an appropriate margin to the stall speed."

"Appropriate margin to the stall speed" - In other words - using the full range of speeds between Vmax and Vls is considered acceptable should you require or wish to do so. With auto thrust active you will not get below this speed anyway, not even when flying in V/S mode (this is another common misconception).

[springbok449]

Thanks for the reference Desipilot.
Ah those valuable instructor support manuals that line pilots are not meant to access... I will try and get hold of a copy as it clearly has some useful info in there.

CP, just for clarification, I dont disagree with the things that you say, I am just enjoying a healthy debate and some useful stuff from fellow pilots.

As they say, there are many ways to skin a cat...

[seventhreedriver]

What is the exact definition on F speed (flap retraction speed), S speed (slat retraction speed) and VLS (lowest selectable speed)?

What is so "unprofessional" about flying above VLS but below F/S speeds, when I don't want to retract the slats/flaps?

And why doesn't the AT go below F/S speed when the speed is managed? Because it does not have any clue as to what you are about to do, retract the flaps or extend them. At S/F speed, you are usually safe to do both so it maintains it.

[Nubboy]

All very good stuff. Had a few discussion points in after a sim check a while ago over exactly these sorts of points. My examiner was unable to justify why it was safe to fly from takeoff to above msa below F speed, but unsafe to fly from msa back to the threshold using the same speed.

As far as I understand it, not only is VLS not just more than 130% of stall speed, it's also dynamic in that it responds to wing loading, and therefore indirectly, to angle of bank.

As a slight aside we have one route where we tanker in to a high-ish intermediate airfield after a fairly short sector and aim to land about 500kg under max landing weight. In the summer watching the newbies try to slow the aircraft to configure, with the amber bit just under green dot which itself is fairly close to the amber ticks for the next flap setting, has my full attention, I assure you. Some even seem tempted to want to use the speed brakes as we start to turn base. However when you do get some flap out, the spread opens right out. So why are the trainers reluctant to let you use that part of the green tape if airbus says you can?

[rudderrudderrat]

Hi Nubboy,

My examiner was unable to justify why it was safe to fly from takeoff to above msa below F speed, but unsafe to fly from msa back to the threshold using the same speed.

It's because on take off and GA, it's permissible to fly at 125% V stall (or whatever Airbus's factor is) but limit bank angle to 15 degs and you are not expected to pull speed brakes.

On the intermediate approach, you fly at a minimum of 130% V stall, bank up to 30 degs, and may pull speed brakes - hence the bigger margin.

Edit. @CP

The whole idea is that Airbus has provided us with a dynamic speed showing us exactly what you are saying, a margin that they have deemed "appropriate"
But that's the problem - it is displaying the instantaneous margin for your present "g" which will change with bank angle and speed brake usage. I'm sure Airbus would be happy for us to fly around a few knots above VLS provided we didn't bank or pull any "g" - but speed brakes usage would be prohibited.

I think I'll stick with their present flaps / speed schedule.

[Nubboy]

Ta for that.

However, since it's all computer generated, and the airbus knows what stage of flight you're at (eg SRS displayed, or perf activated), doesn't it compensate for that already?

My question is quite simple, to me anyway.

If you're in the green arc, even below F speed, and above VLS, and airbus say you can choose any speed down to VLS, why do the trainers give you a hard time when you do it?

[rudderrudderrat]

why do the trainers give you a hard time when you do it

Why would you not be flying the SOP Flap / speed schedule?
Were you overweight and trying to select Flaps 2?

[CaptainProp]

Remeber - SOPs may differ from company to company and as stated before, airbus does not prohibit you from doing it.

Enough on this subject from my side.

Keep it safe.

CP

[Toppled AH]

By the way....it's FLAPS and not FLAP........

[Toppled AH]

What i find very amazing is that all qualified pilots and some instructors study the same books, have the same training, fly the same aircraft but all have different opinions for the exact same subject....

[IXUXU]

Ohh don´t worry...it happens all the time talking about the same girl...

[vilas]

I answered this before. All speeds are flyable upto VLS. You don't see this in manuals because it is not mentioned. However Airbus has clarified this in one of the conferences. The bank angle for angle of attack protection is reduced by 5degrees i.e. at GD it is 45 dgrees at VLS it is 40 degrees. If you are flying with auto pilot or manually with FD you won't exceed the bank.

[737Jock]

Rudderrudderrat. Green dot F and Especially S speed are nowhere near 130% VS. Please don't confuse these speeds with VLS, this question has nothing to do with 130% VS.

The question is completely justified, airbus have provided us with VLS which is the lowest selectable speed that provides a safe margin over VS.
The speed range between VLS and green dot, S or F speed can be something like 50 - 60 kts.
Every takeoff this margin is used, and the bus does bank more than 15 degrees. But on descent airlines prohibit flying i this range between VLS and green dot/S/F.

Now we can come-up with all kinds of imaginary scenarios for the descent/approach case with speedbrakes and bankangles, but I could do the same for the takeoff case. In takeoff this isn't planned nor is it in approach.

The instructor will give a hardtime anytime you don't fly in accordance with company procedures. But technically there is nothing wrong with flying somewhere in between VLS and F, S or O speed.

I have heard people complain about selecting a speed below F/S speed on takeoff (expedite climb for earlier turn in right direction) while the managed speed (same speed) was doing the same for the last 2 minutes or so...

[junebug172]

You guys need to start acting like aviators and actually use the speed tape instead of looking at the letters on it.

[WhyByFlier]

flap speeds close to min managed speed (f, s, green dot)

......is not the name of these speeds. These speeds are called MINIMUM FLAP/SLAT RETRACTION SPEEDS. That is their name, nothing else. (DSC 31-40-AIRSPEED).

As for turning below F or S speed, we regularly do it, and select below for an improved early climb. Places like BCN with their sharp left turn from RWY 25L at 450 AGL.

In the company I fly for (easyJet) we are not allowed to select below these speeds on approach. I know in BA from mates there that they do on approach.

As for limitations to this :

Obstacle clearance, noise abatement, or departure procedures may require an immediate turn after take-off. Provided FD commands are followed accurately, the flaps and slats may be retracted using the normal procedure as FD orders provide bank angle limits with respect to speed and configuration.

[Cough]

Makes me giggle this...

If I want to fly 180kt at 56T on final then if you are in a 319 you need flap 2 (if your SOP isn't to go below 'S'). In a 320 or 318 you can fly it at flap 1...

Same wing, different certification assumptions (I'm lead to believe) hence different speeds....

[Willie Nelson]

In my airline, we cant go below green dot, F or S speed without selecting the next stage of flap, having said that we only mandated it around two years ago in company procedures. Before this guys would apply common sense and not normally go below it anyway.

As pilots we become so used to following everything to the letter of the law, when a law is not written we are often at sea wondering what to do, then someone messes up and....hey presto, there is a new procedure and, if your company is like mine, it takes a few weeks to find out why, then the rumours start.

I believe that Airbus has not specified a restriction on selecting a speed on approach below the manoeuvring speeds because they, unlike modern Airline management allowed some PIC discretion to fly the aircraft they way the PIC thinks it should be flow within the normal envelope.

Our reactive airline safety departments however remove all discretion, I sometimes wonder if I should be retitled pilot under command (of airline management) rather than pilot in command.

Whinge complete, you have the comms.

[Down...2 greens]

Perhaps the Flight Crew Training Manual might be of interest.

A320 FCTM NO-110 (Approach): "A speed below the manoeuvring speed of the present configuration may be selected provided it is above VLS. When the ATC speed constraint no longer applies, the pilot should push the FCU speed selector to resume managed speed."

The disadvantage, of course, is reduced margin in case of unexpected turbulence (wake vortex encounters aren't unheard of on approach...) or perhaps the next flap selection being made in the wrong direction!

In the after takeoff scenario, once in the clean configuration, you're only likely to want to deviate from the managed speed profile to achieve either best angle (green dot) or best rate (considerably faster than green dot speed). As Airbus put it: "Pilots should be aware that it is possible to select and fly a speed below green dot, but there would be no operational benefit in doing this" (A320 FCTM NO-060 - Climb).

[Field In Sight]

www.pprune.org/tech-log/458009-vls-speed-increase-turn.html#post6588270

Vls is only dynamic regarding change of config ie slat/flap/spoiler position.

Not loading. Discussed in the above link.

[Natstrackalpha]

Why don`t you just say that `F` spd is to protect the flaps (after t/o) but `S` spd is the minimum speed to be selecting ( or indeed, merely considering) flaps up . . . .?

I mean, thats why some SOPS write "S" spd - flaps up" responded with `spd check` pause . . . . . . . . . . selects flaps up - "flaps up" instead of just bring in them straight up bang on `S` spd.

It, does stranger stuff like turn and burn without stalling in config 2 after takeoff, at a seemingly low, low spd - so it may be even stranger and thus more capable at 180 clean aprt from the fact that the stall spd is greater in a turn . . etc.

The idea of selecting your own spds by which you, the pilot, will have the amount of flaps you consider you need sounds like a wiser choice, even though the bloody thing is hardly going to stall - and yet in a climbing turn when heavy at low alt this does give one a sense of uneasiness. Flap referring to Flap setting or Flaps referring to Flap setting(!)

ahhh, the dicotomy of flying or being flown.

If you combine all the efforts of the onboard computors, they seem to form a node, a cerebral synapse called the Lift computor perhaps - so, if we are flying a computor working on our lift, then just as the good old a/p has the accuracy and handling characteristix way beyond our own ability to fly so accurately straight and level - so too may this FAC and ELAC combined (not to mention all the rest) . . piece of kit be able to fly us and provide enough lift, even if our instincts are telling us that for this wt and spd, we should not be doing it.