Is VLS kind of speed can't be violated in A320 family ?

[Todd Rich]

VLS is lowest selectable speed

This is one of the finer points in understanding the Airbus. VLS is the lowest selectable speed (non-managed auto-thrust engaged). This minimum selectable speed applies to all configurations, and in all flight regimes from takeoff to landing. It is important to point out that lowest selectable is to be distinguished from lowest flyable. speed. This distinction is worth noting because it is possible for the aircraft to fly below VLS, even while VLS is selected. For example, turbulence, or a sudden pitch change up. There is no ability to select below VLS unless the auto-thrust is turned off. The Airbus engineers knew that it is possible for the aircraft to find itself below VLS, but at the same time that possibility is engineered into the jet, and the auto-thrust will be working to get itself back above VLS the moment it goes below VLS. The smart Airbus pilot knows that the safe envelope of this jet is to be able to select down to VLS. And the smart Airbus pilot knows that this is a perfectly safe speed. You might have noticed that VLS up at cruise altitude is somewhere around 40 knots above Alpha Max (top of red zipper), and Alpha Max represents 1.1Vstall. With that said there is no good reason I can think of up at cruise altitude to fly the aircraft below Green Dot because once the aircraft slows below Green Dot, the jet is below L/D Max, and that would result in more fuel burn. Holding speed should always be at L/D Max for that very reason, and that's the reason why Managed holding speed is always Green Dot. Green Dot give the maximum endurance fuel burn, and that's exactly what a pilot wants in a holding pattern. I am surprised sometimes that experienced pilots will think that it's good airmanship to add speed to Green Dot in a holding pattern. Doing that only increases fuel burn. There is a tremendous amount of stall margin on an Airbus at Green Dot, so that's where you want to be when max endurance is the goal. Holding is exactly that situation.

It is also important to point out that the lowest selectable speed managed and clean is Green Dot, after that, the characteristic speeds are the minimum speeds as the aircraft is configured. In selected mode, however, it is always VLS that is your lowest selectable speed, and that is important to understand. For example, if one finds themselves in a radar pattern at a congested airport, and perhaps you might be on a 25NM downwind at 5,000 feet. The controller asks you to slow to 190. The smart Airbus pilot will look at the VLS, and as long as 190 is above VLS, he will not go to Flaps 1. He will realize the jet is fully maneuverable down to VLS in any configuration, and as such, will fly the jet clean at 190 knots. That's smart because it saves fuel, and again, in no way safety is compromised. To the contrary, safety is enhanced because fuel is being saved that might be needed in the case of a longer delay and a diversion. This issue especially holds true when going from Flaps 1 to Flaps 2 because the amount of increased drag going from Flaps 1 to 2 is quite significant. So if on that same 25 mile downwind, ATC slows you to 170, you want to stay at Flaps 1, even if the nose is a little high. As long as the jet is above VLS, you are safe and solidly in the envelope, and you are saving fuel - a lot of fuel.

Bottom line, understanding the lowest selectable speed is VLS is a safe speed and a smart speed in certain cases, will make you a much better Airbus pilot.

[FlightDetent]

Have you tried going around from CONF 1 at 170 kts recently?

[FullWings]

Originally Posted by LegiossTypeH

Thanks for you all give me so many information and opinions,
so may I conclude as below ?

1. VLS is not a limitation nor a speed pilot always have to be at or above, but only a lowest selectable speed for autothrust.
2. Pilot can fly a speed below VLS momentarily with a good reason. It is a common sense, or check/test standard in most company, not words in FCOM or FCTM.
3. VLS is a speed with sufficient margin to stall or activate Airbus protection.
4. In a check/test, normally speed tolerance is +10kts/-5kts.

That's what and why I answered when he asked how do I feel :
I confess I'm not flying good, but I don't violate anything, and I'm still in a positive climb, which is the most important while in such low altitude with a plane get into the runway. I don't understand why I should wait until the power comes up just to maintain a speed at or above VLS, or the manage speed target. It is a high bypass ratio Engine.

I’m not Airbus qualified but I think most TREs assess in a similar manner whatever aircraft is involved.

If you’re uneasy with someone’s general standard of operation under check, and you think they need more training and/or to come in on another day as there may be external factors that are influencing their performance, then a point where formal test parameters are breached is somewhere to “hang your hat” on the paperwork. It may have been a debrief item otherwise, or you were exemplary elsewhere but had a picky trainer. Self-analysing, what do you think, and what will you do differently to pass your next detail with flying colours?

[vilas]

In a test overall performance is considered. Perhaps dropping speed below VLS was the last straw. Flying below VLS is a minus if alongwith some other minuses can result in a failure. Instead of trying to find justification if you can find why it happened and how you planned to avoid next time will be productive.

[FlightDetent]

It's been 3 years since the OP opened the thread, surely he's moved to a higher level by now.

[pineteam]

in my outfit: For the PPC, we have a tolerance of +-10kt on the speed for single engine go around. A momentary drop below the target speed (limited to 10 Kts) is acceptable during go around phase.

[Todd Rich]

I assume you mean ATC tells you to go around on final, and you're configured to Config 1, and doing 170? That scenario would be unusual in that it is a requirement, at least at our operation, to be fully configured by 1,000' agl. So if I were at 170, and in Config 1, that would have to be happening a good ways out on final, or maybe on some kind of extended vector where ATC was asking me to do 170 knots. But if your question is rhetorical in the sense that your suggesting that a go-around from Config 1 is unsafe, consider that if ATC asked you to abort the approach, and you were at 170 knots config one, that would not be the same type go around as text book one done, fully configured and down near the ground. That would be a smooth application of power without pitching the nose way up. In effect, not really a go-around, in any case, very safe, very normal - unless the pilot made it unsafe by ripping the nose up. But why would he or she do that? So that scenario of going around from 170, Config 1 needs to be explained in more detail for me to visualize what you are visualizing.

[rexarus]

I would also point out that Green Dot and VLS are often the same speed up at cruise altitude. So that means managed holding would be at VLS in those cases.

[vilas]

Originally Posted by rexarus

I would also point out that Green Dot and VLS are often the same speed up at cruise altitude. So that means managed holding would be at VLS in those cases.

At cruise altitude you can't hold at VLS because during a turn Valpha prot will rise and trip the AP. Higher levels ICAO holding speeds are Like M.8 or above 340 it's.83.

[Romasik]

No. It can be violated. It cannot be selected. You can legally fly at VLS and it may momentarily go below due to aerodynamic or weather conditions. You should not intentionally fly below VLS and if you miss it and didn't correct, then it may be a failure point.