Airbus Approch Speed: VLS versus 'S' Speed
 

What is the lowest speed that can be safely flown on approach before taking flap2? Is it 'S' speed or VLS?
I have asked this question to a few other pilots and there seems to be two very distinct opinions:

1. NEVER reduce speed on approach below 'S' speed without taking flap2.

2. Generally take flap2 at 'S' speed but when operationally necessary you can safely reduce speed to between 'S' speed and VLS without taking flap2.

I personally agree with those in group 2 but I would be interested to hear were you, and your company SOP's, stand on this?

The orange company tells you not to reduce below S in flaps 1.

In my previous company option 2 was accepted. (they operated standard Airbus SOP)

In my understanding you can fly the airbus anytime between Vls and Vmax. S and F are retract speeds and in no way resemble an aerodynamic signifant speed with regards to maneuvering (both have entirely different margins, and are represented by different point on the L/D curve).
However they are used as managed speed targets by the FMGS, I guess for simplicity.
S and F are suitable as speed targets because they always are between Vls and Vmax and especially S is a good ballpark speed for the intermediate approach. Assuming that you would always fly a decelerated approach there would be no need for actual flap maneuvering speeds. But how different is reality. I would be happy to fly below S speed with flaps 1. (I am guessing that the delta Vref for flaps 1 would result in a Vapp below S anyway). However my company does not allow it.

IMHO:
1. If ATC want 180K, and 'S' is say 183K, F1 will give you lower fuel flow and acceptable. As you get further below 'S' I get uncomfortable with the high nose attitude. However, the min legal speed is VLS...
2. Getting near VLS in this scenario is going a bit too far - you cannot use S/B without it powering up against you etc.

I don't believe BA's SOPs are 100% prescriptive in this area, and that's probably the best way. Often I will fly a bit under 'S' @ 180K F1 but as the G/S approaches take F2 to use the drag down the slope (F1 it will accelerate), and avoid the F2 "balloon" while trying to hold the G/S...

There was a similar thrtead smtm ago, check the search.
Once we reduced speed very close to VLS with F1. You know, the bird becomes a bit shaky. You feel it. (Oh it was so nise morning appr to Amsterdaam!).
Since then I prefer to use F2 at low speeds.
Nothing at SOPs though.

The clue is in the definition .... Vls = lowest selectable speed. It is designated as such by Airbus and therefore is safe.

It is another matter altogether as to what is sensible when it comes to normal operations. I am (or was) of the brigade that flying below S speed [10kts or so] was fine on a short term basis in good (non-turbulent) conditions rather than take the extra drag associated with Flap 2.

VLS is the lowest SELECTABLE speed with the autothrust engaged. It is not the Alpha Floor or Alpha Prot speed. On the approach, S and F speeds are used by the autoflight system as target/minimum speeds for flap 1 and Flap 3 config. The aircraft can be safely flown below this speed all the way down to the Vref for your current configuration but you may encounter turbulence which could lower the buffet margin.

Operating below S speed in config 1 is not in itself dangerous and is often used by European and US operators to fly 180 when requested by ATC. However, many operators do not allow you to do this and use S speed as the minimum for Config 1. Use whatever your company SOPs say. If they are silent on this point it is probably because the management has decided to leave it up to the pilot's discretion.

On takeoff/goaround F and S speeds are the minimum speeds for retracting flaps to the next appropriate setting.

In the Airbus Flight Crew Training Manual, under Normal Operations, Approach General, 02.100....
The second paragraph says...A speed below the maneuvering speed of the present configuration may be selected provided it is above VLS.

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.

It may bite thee.

I believe S speed indicates the lowest speed in config 1, Minimum speed with slats out. Below this speed you should have Flap 2 selected. Flying near VLS is dodgy and as has been noted before, on an intercept where the aircraft can command upto 30 degrees of bank to pick up the LOC, you could end up with egg on your face as the aircraft goes into Alpha Floor! If you fly 321 you will definitely need flap 2 at 180 knots as S speed tends to be around 200 knots, I have seen a number of pilots make this mistake.:ok:

With the utmost respect to your opinion, I am sure there is plenty of official reference that state the exact opposite. For one, after departure you will select flap 1(+F) while passing F speed, well below S speed, alebeit accelerating. Same applies for 1 > 0.

FlightDetent
Big difference between "conf 1" below S speed and "conf 1+F" below S speed.

F and S...........
 

As far as i understand it, and without going to the books (so prepared to be shot down!!), flying at s speed gives you the full flight envelope with which to manouvre, as garuanteed by toulouse. If you go below this without taking flap, you haven't got the full envelope to play with.

This is how it was described to me, i've only just finished my line training, so as ever would welcome any comments.............. clean though please!!

protections
 

it's in the fcoms somewhere but Green dot, F and S speeds give you full 25 degrees bank protection to those speeds less 3 knots. This protection then decreases as you continue towards VLS.
Bottom line, i'd fly the Green dot, F,and S speed but at very heavy weights and when straight and level i've set below the S speed to get Flap 2 out without busting the Flap limit speed.

FLIGHT DETENT........ I think you had better start reading your manuals again, looks like you could do with a refresh. Have a think about what RIGHT WAY UP has written and go look in your manuals, you might be surprised. If you still haven't grasped it, I was discussing the approach not after take off.:ugh:

I am quite aware that it is approach speed discussion and also, that 1(+F) makes a huge difference and is not a very good example. No need to argue with RWU.

As you do fly the A321 you also know that at 89t the S speed is 220 kt and flaps would auto-retract at 210, so you are flying as designed 10 below S speed with slats only - and it is completely normal. Same applies when passing S speed to clean up, again you are flying below green dot with no LE or TE devices at all (I hope I am correct to assume that you would claim it is incorrect to fly below green dot in clean, just like you say CF-2 is required to go below S speed).

As far as the books go:
FCTM Ch2 Intermediate Approach / DECELERATION AND CONFIGURATION CHANGE FCOM 3.04.10 p2
S speed definiton: F speed definition: Now, everybody agrees that it is safe (nothing more than that) to fly V2 with engine out. V2 is: Minimum value equal to 1,13 Vs for the corresponding configuration.

Hence my assumption that is indeed a very good practice but not a reqirement as per original Airbus design.

FLIGHT DETENT.... I am glad you took my advice and got your head in the books, keep studying, one day you will get there.

Passing S speed cleaning up..... you do not fly below green dot without L/Edge devices as they take time to retract unless your Airbus has very very very quick retract on it, mine retracts flap etc over a period of time, by which time you have accelerated beyond green dot.

Blimey you must be hard work on the flight deck.:ugh:

No, I am downright dangerous, flying 15 knots above VLS and other stunts. :cool:

Flying below S speed
 

What about flying below the S speed with a selected speed and you have an engine fail? Do you have enough energy to fly?

I like Flight Detent's referenced explanation of his opinion, and its one I share. Perhaps if Iva Harden would make a similar argument for his/her position, and focussed a little less on patronising, we might understand that point of view too.

For those who would choose not to fly slower than S speed - Would you fly below F speed in conf 3? If the answer is no - what would you use as Vapp on a conf 3 landing?

Well, what happens if you lose an engine at V2? Do you have enough energy to fly?