Airbus Approch Speed: VLS versus 'S' Speed
What is your call out for going around? "Go around, flaps", by any chance?
If you do that with flaps 1 and speed below S, you're in trouble.
For that reason in our outfit it's a no-no. Big German airline.
If you do that with flaps 1 and speed below S, you're in trouble.
For that reason in our outfit it's a no-no. Big German airline.
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safelife
If you are going around in Conf1 or Conf2 there is no need to retract flaps. They will meet gradient requirements since they are supposed to meet in CONF3. Official airbus position is all speeds up to Vls are flyable but bank margin for triggering protection reduces. F and S are flap retraction speeds.
If you are going around in Conf1 or Conf2 there is no need to retract flaps. They will meet gradient requirements since they are supposed to meet in CONF3. Official airbus position is all speeds up to Vls are flyable but bank margin for triggering protection reduces. F and S are flap retraction speeds.
If you activate the approach phase and manage the speed will it go to VLS or will it target S F speed as appropriate? If you apply speed brake what happens to your VLS? Take flap 2. The fuel penalty is minor, the deck angle is better and the margin for manoeuvre higher. I don't fly at Vne nor do I fly at VLS.
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What I stated is airbus answer. Obviously it is short term solution if you expect to fly below that speed for a considerable time one should reduce speed after going to higher configuration.
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 after a touch and go.
Becomes 1.23 VS, after retraction of one step of flaps.
Becomes 1.28 VS, when in clean configuration.
Note: If in CONF 0 VLS were 1.23 VS (instead of 1.28 VS), the alpha protection strip
would hit the VLS strip on the PFD.
Above 20 000 ft, VLS is corrected for Mach effect to maintain a buffet margin of 0.2 g.
In addition, VLS increases with speed brakes extension.
F : Minimum speed at which the flaps may be retracted at takeoff.
In approach, used as a target speed when the aircraft is in CONF 2 or CONF 3.
Represented by “F” on the PFD speed scale.
Equal to about 1.18 VS to 1.22 VS of CONF 1+ F.
S : 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 1.22 VS to 1.25 VS of clean configuration.
O : Green dot speed.
Engine-out operating speed in clean configuration.
(Best lift-to-drag ratio speed).
Also corresponds to the final takeoff speed.
Represented by a green dot on the PFD scale.
Below 20 000 ft equal to 2 × weight (tons) +85
Above 20 000 ft, add 1 kt per 1 000 ft
The above is from Airbus. The reason you can use auto thrust and select and fly down to VLS is that is may be needed to non normal approaches (flap or slat problem etc). Or you may be heavy weight in some types (345/6, 380) and need to select below S or F speed to establish below Vfe.
Computed by the FAC, based on aerodynamic data, and corresponds to 1.13 VS during
takeoff, or after a touch and go.
Becomes 1.23 VS, after retraction of one step of flaps.
Becomes 1.28 VS, when in clean configuration.
Note: If in CONF 0 VLS were 1.23 VS (instead of 1.28 VS), the alpha protection strip
would hit the VLS strip on the PFD.
Above 20 000 ft, VLS is corrected for Mach effect to maintain a buffet margin of 0.2 g.
In addition, VLS increases with speed brakes extension.
F : Minimum speed at which the flaps may be retracted at takeoff.
In approach, used as a target speed when the aircraft is in CONF 2 or CONF 3.
Represented by “F” on the PFD speed scale.
Equal to about 1.18 VS to 1.22 VS of CONF 1+ F.
S : 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 1.22 VS to 1.25 VS of clean configuration.
O : Green dot speed.
Engine-out operating speed in clean configuration.
(Best lift-to-drag ratio speed).
Also corresponds to the final takeoff speed.
Represented by a green dot on the PFD scale.
Below 20 000 ft equal to 2 × weight (tons) +85
Above 20 000 ft, add 1 kt per 1 000 ft
The above is from Airbus. The reason you can use auto thrust and select and fly down to VLS is that is may be needed to non normal approaches (flap or slat problem etc). Or you may be heavy weight in some types (345/6, 380) and need to select below S or F speed to establish below Vfe.
vilas
Our SOP for going around is to call for flaps, whatever the setting was. Also you're prone to do that automatically, I don't believe Airbus says "only when conf 3 or full " in their SOP.
That exactly is the reason why Airbus uses S speed as the target with managed speed, to be in position to go around and retract flaps from there.
Our SOP for going around is to call for flaps, whatever the setting was. Also you're prone to do that automatically, I don't believe Airbus says "only when conf 3 or full " in their SOP.
That exactly is the reason why Airbus uses S speed as the target with managed speed, to be in position to go around and retract flaps from there.
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safelife
Horses for courses. If you had speed below S then don't have to retract. Below is from Airbus:
When landing configurationis not established (CONF1 or CONF2) there is no particular need to retract theflaps one step as there is no drag issue, and therefore, no performance impact.However, standard go around procedure (GO AROUND – FLAPS) could be applied,even when in CONF1, provided TOGA detent is reached prior flaps retraction (toensure GO AROUND phase engagement). A/THR and FD’s will maintain VLS, and SlatsAlpha / Speed lock function will inhibit slats retraction if necessary
Horses for courses. If you had speed below S then don't have to retract. Below is from Airbus:
When landing configurationis not established (CONF1 or CONF2) there is no particular need to retract theflaps one step as there is no drag issue, and therefore, no performance impact.However, standard go around procedure (GO AROUND – FLAPS) could be applied,even when in CONF1, provided TOGA detent is reached prior flaps retraction (toensure GO AROUND phase engagement). A/THR and FD’s will maintain VLS, and SlatsAlpha / Speed lock function will inhibit slats retraction if necessary
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The other interesting situation relevant to this discussion would be an overweight landing that required conf 3 for MISAP perf restrictions. Our SOP is to go around in conf 1+F (despite the fact that planning tables exist for missed approach climb limiting weights for a go around in conf 2). If this were to happen in the later stages of approach - at or around Vapp, one will be going around well below S speed. Obviously a situation we'd like to avoid in real life, but its no dramas in the sim.
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Well , I think everyone here understands that the lowest speed that can be flown is VLS and it has been properly quoted.
But here how it works: when someone from the management (pilot) is scared of something because of his own conception ,generally it will be prohibited for the whole community of pilots of that airline.
But here how it works: when someone from the management (pilot) is scared of something because of his own conception ,generally it will be prohibited for the whole community of pilots of that airline.
Sadly citation2, most who like to fly close to VLS have no idea of the implications of doing so, and can't quantify any gain in performance for being there. Just knowing it's the lowest selectable speed is not enough knowledge. Unless you are in a non normal approach, or heavy weight needing to get below Vfe, I can't see why you need to be there.
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Good airmanship and sound judgment will help you understand the issue. The discussion is not to fly at VLS and flaps 1 during approach but merely close to S speed. So if ATC requires 180 kts while your S speed is at 183 kts , you won't fall off the sky because of 3 kts below S. Airbus confirms that the upper limit is Vmax and Lower limit is VLS , that does not mean you will fly at those limits on a routine basis, but only in case of emergency / abnormal.
But being close to S to satisfy an ATC requirement is a different story , again sound judgment is required , depending on weather, weights etc.., how far below S?
It is not clear cut , black or white . In gusty winds that would not be appropriate, in normal condition , few knots below S , will not hurt you.
By the way on final configuration , flaps full , how far are you from VLS?
But being close to S to satisfy an ATC requirement is a different story , again sound judgment is required , depending on weather, weights etc.., how far below S?
It is not clear cut , black or white . In gusty winds that would not be appropriate, in normal condition , few knots below S , will not hurt you.
By the way on final configuration , flaps full , how far are you from VLS?
With flaps full VLS is Vref. So you fly at Vapp which is the same as any other aeroplane. You see my point then.
It hasn't been mentioned so far so apologies if I'm telling you how to suck eggs as quoted already its fine to go below manuevring speed provided you stay above Vls, BUT be very cautious about getting too close to Vls if you have any turns to make eg intercepts. Vls will rise considerably in the turn when in this portion of the drag curve.
This seems to be a common confusion: There are three low speed warning strips at the bottom of the speed scale, one on top of the other. The top one (usually) is VLS and it only changes with a change of wing shape - i.e. Slats, flaps and speed brakes.
V alpha prot and V alpha max are usually below VLS and they do change with wing loading. Alpha Prot speed can get above VLS sometimes during manoeuvres.
From FCOM DSC-31-40:
1)Minimum Selectable Speed (VLS)
The top of the amber strip [- they mean a hollow rectangle outined in amber] along the speed scale indicates this speed. It represents the lowest selectable speed providing an appropriate margin to the stall speed.
(2)Alpha Protection Speed
The top of a black and amber [- horizontal stripes] strip along the speed scale indicates this speed.
It represents the speed corresponding to the angle of attack at which alpha protection becomes active.
(3)Alpha MAX Speed
The top of a red [-solid red] strip along the speed scale indicates this speed. It represents the speed corresponding to the maximum angle of attack that the aircraft can attain in pitch normal law.
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I am sorry Call it VREF or XYZ your margin to VS1g is shorter in final configuration than with Flaps 1 . Well initially just look at your PFD and watch how far is VLS with Flaps 1 and compare it to final configuration VLS.
Now let me Help you with this :
S : Equal to about 1.22 VS to 1.25 VS of CLEAN configuration
I would like to emphasize on "Clean " because it means that your margin to VS1G is based on a higher speed ( green dot ) and not actual configuration , hence greater margin to VS1G . That is why VLS is so low in Flaps 1 . Notice how VLS goes down when you select Flaps 1.
From Supplementary - Definition:
At Green dot speed VLS= 1,28 VS1G
S speed : 1,22 to 1,25 VS1g of CLEAN. Let's say an average of 1,23
So your margin to VS1G in S speed is 1,23X1.28=1,57 VS1g
Now let's compare this value to the tables available on Limitations :
For a weight of 60 T , VS1G is 120 kts in Flaps 1+F and 125 in Flaps 1
For a weight of 60 T , S speed is 185 kta
185/120=1,54
Close enough isn't it ? With the table I found a margin of 54% to VS1g and with the calculation I found 57% of margin to VS1g.
Let's say 55%. S speed is 55% greater than VS1g.
Now let's come back to final configuration . What is your actual margin to VS1g? 23% right? Vref= 1,23 VS1g
So where do you think you are closer to a stall ? You accept to fly with 23 % of margin to VS1g and not 55% , just because they call it VREF?
Now let me Help you with this :
S : Equal to about 1.22 VS to 1.25 VS of CLEAN configuration
I would like to emphasize on "Clean " because it means that your margin to VS1G is based on a higher speed ( green dot ) and not actual configuration , hence greater margin to VS1G . That is why VLS is so low in Flaps 1 . Notice how VLS goes down when you select Flaps 1.
From Supplementary - Definition:
At Green dot speed VLS= 1,28 VS1G
S speed : 1,22 to 1,25 VS1g of CLEAN. Let's say an average of 1,23
So your margin to VS1G in S speed is 1,23X1.28=1,57 VS1g
Now let's compare this value to the tables available on Limitations :
For a weight of 60 T , VS1G is 120 kts in Flaps 1+F and 125 in Flaps 1
For a weight of 60 T , S speed is 185 kta
185/120=1,54
Close enough isn't it ? With the table I found a margin of 54% to VS1g and with the calculation I found 57% of margin to VS1g.
Let's say 55%. S speed is 55% greater than VS1g.
Now let's come back to final configuration . What is your actual margin to VS1g? 23% right? Vref= 1,23 VS1g
So where do you think you are closer to a stall ? You accept to fly with 23 % of margin to VS1g and not 55% , just because they call it VREF?
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In airbus we don't think of stall but triggering protection. Quoted below is from airbus presentation on the subject:
Manoeuvring capability
However if ATC speed constraint:
Margin could become small in turbulent conditions, or with high bank angles.
If such conditions are anticipated consider CONF change.
Manoeuvring capability
- At V2, one engine out: stabilised turn at 30 degrees bank before alpha max.
- At V2+10 all engines operative: Stabilised turn at 40 degrees before alpha floor.
- At green dot: Stabilised turn at 45 degrees bank before alpha prot.
- At Vls (final take off up to landing):Stabilised turn at 40 degrees before alpha floor.
However if ATC speed constraint:
- Selected speed
- Possible to fly below manoeuvring speed down to Vls. It enables standard manoeuvres.
Margin could become small in turbulent conditions, or with high bank angles.
If such conditions are anticipated consider CONF change.
- Resume to managed speed when out of ATC constraint.
Last edited by vilas; 10th Feb 2017 at 06:07.
How much manoeuvring are you doing when at Vref? Hmmm I wonder if that's why there is a difference in the margin.
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How much are you supposed to manoeuvre with Flaps 1 and speed 180 ? If it is just to satisfy an ATC speed restriction when S speed is few kts higher?
VFe flaps 3 is 185 kts . Take flaps 3 and fly 180 kts , you will have less chance to fall off the sky.
VFe flaps 3 is 185 kts . Take flaps 3 and fly 180 kts , you will have less chance to fall off the sky.
Citation, so you see my point then. Some pilots don't understand what they are doing, and don't understand why you can only fly selected speed when below manoeuvre speed.
