Hello guys...i'm a first officer of the A320 in the airliner of south america and i have a question about the VLS and other about Fuel System!

* FIRST QUESTION...

In the FCOM manual the VLS mean: "lowest selectable speed", OK? In the theory...the aircraft not fly in the speeds lowest of the vls. The FCOM say too: "In the case of speed reach the vls the automatism of the aircraft will increase the thrust and will mantain the speed in the VLS".

Now....my question!!!

I was flying and my captain during the descent activated the speed breaks, so i see the vls line increase and enter in the speed reference line and the automatism of the aircraft not increase the thrust. The aircraft just kept the speed that was already.

How do you explain this?

* SECOND QUESTION

The FCOM 1 says that when the central tank is more than 250kg and any internal tanks less than 5,000 kg the mode selector push button will light in fault.

What is the logic of the system? Why does this happen?

Very grateful to anyone who can answer me!!

I'll get back to you with further information, but what I can tell you from flying the airbus now for about 6 years, that the airbus doesn't always follow the FCOM exactly.

Airbus makes "updates" to the software and then will often not update the manuals - because you "might" be flying the older software, I guess.

In any case, I've noticed the same thing, and I think the aircraft has tolerances in the software, I believe, outside of what the book says. I've seen it go below VLS and also go in to the red band, all on autopilot, without it doing anything - trying to be "smooth" I guess. However, before it gets too far, the FADECS do seem to respond. In turbulence many airbus pilots prefer the authothrottles OFF for the very reason that they are too "Smooth" and don't respond when the airplane gets below VLS quickly enough.

I tell all new airbus pilots that the manuals are more like guidelines than facts .

As for the fuel issue, again, there have been "mods" to the fuel pumps that I don't think are reflected in the FCOMs. I'm used to using pounds rather than kg, so I may be off on that, but for a long while airbus at a revision about turning off pumps when the center tank got below a certain level - until the "mod" was done, but I don't know about your company, but the two airbus companies I've flown for are very poor on communicating which airplanes have which mods.

You figure it out eventually but a lot of it is just experience, which can be very frustrating.

Thanks for the question!

Hi:
The trick is to follow the FMA carefully.You are exactly right about the VLS definition but when you have "THR" instead of "SPD" on your FMA the scenario is diffrent.
When you use LVL/CH for exmple,pitch got full authority to keep your speed by giving more nose down in descend,on the other hand when you use speed brake the VLS rise up to (green dot-1)
so the only way to increase speed is to reach more nose down which has no effect in ur case,becuz your bird is hang on speed brake !!! so you can't see anything becuz you disable your aircraft youself.
Be carefull in turb conditions and high weight
together make the sky more safe.