Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

F, S, green dot speeds

Tech Log The very best in practical technical discussion on the web

F, S, green dot speeds

Old 28th Apr 2010, 11:59
  #1 (permalink)  
Thread Starter
 
Join Date: May 2009
Location: Russia
Posts: 81
F, S, green dot speeds

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
pensador is offline  
Old 28th Apr 2010, 12:11
  #2 (permalink)  
 
Join Date: Aug 2002
Location: Up north
Posts: 1,648
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
CaptainProp is offline  
Old 28th Apr 2010, 12:48
  #3 (permalink)  
 
Join Date: Oct 2009
Location: UK
Posts: 1,271
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."
rudderrudderrat is offline  
Old 28th Apr 2010, 20:16
  #4 (permalink)  
 
Join Date: Mar 1999
Location: UK
Posts: 365
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
Nubboy is offline  
Old 29th Apr 2010, 02:07
  #5 (permalink)  
 
Join Date: Jun 2001
Location: Fragrant Harbour
Posts: 4,734
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!
Dan Winterland is offline  
Old 29th Apr 2010, 04:06
  #6 (permalink)  
Thread Starter
 
Join Date: May 2009
Location: Russia
Posts: 81
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!
pensador is offline  
Old 29th Apr 2010, 05:44
  #7 (permalink)  
 
Join Date: Jun 2001
Location: Fragrant Harbour
Posts: 4,734
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.
Dan Winterland is offline  
Old 29th Apr 2010, 06:04
  #8 (permalink)  
 
Join Date: Jan 2005
Location: The Underside
Posts: 65
Dan

Retract the flaps after the turn is complete.

Saves the puckering!

Fx
Feather Boa is offline  
Old 29th Apr 2010, 11:23
  #9 (permalink)  
 
Join Date: Jul 2000
Location: Blighty
Posts: 564
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...
springbok449 is offline  
Old 29th Apr 2010, 12:52
  #10 (permalink)  
 
Join Date: Sep 2005
Location: Everywhere and Nowhere but not at Home
Posts: 283
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
Airbus_a321 is offline  
Old 29th Apr 2010, 13:40
  #11 (permalink)  
 
Join Date: Aug 2002
Location: Up north
Posts: 1,648
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
CaptainProp is offline  
Old 29th Apr 2010, 13:49
  #12 (permalink)  
 
Join Date: Jan 2001
Location: home
Posts: 1,471
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!
Right Way Up is offline  
Old 29th Apr 2010, 14:24
  #13 (permalink)  
 
Join Date: Aug 2002
Location: Up north
Posts: 1,648
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.
CaptainProp is offline  
Old 29th Apr 2010, 14:49
  #14 (permalink)  
 
Join Date: Mar 1999
Location: UK
Posts: 365
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
Nubboy is offline  
Old 29th Apr 2010, 16:30
  #15 (permalink)  
 
Join Date: Jun 2001
Location: Fragrant Harbour
Posts: 4,734
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.
Dan Winterland is offline  
Old 29th Apr 2010, 17:02
  #16 (permalink)  
 
Join Date: Jul 2000
Location: Blighty
Posts: 564
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
springbok449 is offline  
Old 29th Apr 2010, 17:43
  #17 (permalink)  
 
Join Date: Feb 1998
Location: Formerly of Nam
Posts: 1,595
...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.
Slasher is offline  
Old 29th Apr 2010, 21:17
  #18 (permalink)  
 
Join Date: Mar 1999
Location: UK
Posts: 365
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.
Nubboy is offline  
Old 29th Apr 2010, 21:33
  #19 (permalink)  
 
Join Date: Aug 2002
Location: Up north
Posts: 1,648
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.
CaptainProp is offline  
Old 29th Apr 2010, 21:46
  #20 (permalink)  
 
Join Date: Oct 2009
Location: UK
Posts: 1,271
@ 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)
rudderrudderrat is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.