Fenix A320. Descent in managed mode except speed.

[Fiorentoni 4,483]

1 hour ago, Vitold69 said:

Exactly. In managed mode plane should be slowed down by spoilers not by automatically (FMGS managed) decreasing its descent rate. 

That's absolutely not what he said. He actually said the opposite, that the plane *will* react to manual speed changes.
I don't know how many people you need to tell you that your assumptions and understanding of how the AP modes work (in like every single airliner) are wrong, fundamentally wrong. Tom_L above even cited the FCOM where it clearly states that it will fly the FCU selected speed if you choose selected speed mode. And again, that's not an Airbus thing, it's how all the FLC/LVLCH/IAS etc. AP modes worked for 60 (?) years.

[Bobsk8 12,960]

13 minutes ago, Fiorentoni said:

That's absolutely not what he said. He actually said the opposite, that the plane *will* react to manual speed changes.
I don't know how many people you need to tell you that your assumptions and understanding of how the AP modes work (in like every single airliner) are wrong, fundamentally wrong. Tom_L above even cited the FCOM where it clearly states that it will fly the FCU selected speed if you choose selected speed mode. And again, that's not an Airbus thing, it's how all the FLC/LVLCH/IAS etc. AP modes worked for 60 (?) years.

Don't you love it when someone asks a question, you give them an answer, and then they try and tell you , you don't know what you are talking about.  😉

[Tom_L 558]

1 hour ago, Vitold69 said:

In managed mode plane should be slowed down by spoilers

In the discussed situation (DES mode with SELECTED speed) the spoilers may be used to support slowing down the airplane and thus minimize VDEV, and as the autopilot has no authority over them, it remains pilots discretion. It is also worth noting that in MANAGED speed the use of spoilers is not recommended to slow down the plane while on or below glide path, because the glide path calculation is based on ECON descent speed and you may end up with autothrust adding thrust in order to not fall below. Spoilers are generally considered means to manage excess energy.

[Vitold69 47]

2 hours ago, Tom_L said:

In the discussed situation (DES mode with SELECTED speed) the spoilers may be used to support slowing down the airplane and thus minimize VDEV

The initial question was - does real world Airbus 320 autopilot DECREASE DESCENT RATE (Selected Speed Mode) in order to get selected lower speed as soon as possible? Fenix's does. Ruining vertical navigation path the same time.

[martinboehme 586]

4 hours ago, Vitold69 said:

Exactly. In managed mode plane should be slowed down by spoilers not by automatically (FMGS managed) decreasing its descent rate. 

Here's an example of a real A320 in the situation we're discussing here (speed selected, descent managed), watch from 3:33:

Some points to note:

• We can tell the speed is selected because the speed is displayed in blue.
• We can tell the descent is managed because the vertical mode is "DES".
• The aircraft is high on profile (and continues to become ever higher).
• Nevertheless, the autoflight system prioritizes achieving the selected speed over maintaining the vertical profile.

[Aamir 2,913]

15 hours ago, Vitold69 said:

The initial question was - does real world Airbus 320 autopilot DECREASE DESCENT RATE (Selected Speed Mode) in order to get selected lower speed as soon as possible? Fenix's does. Ruining vertical navigation path the same time.

Yes. It does. 

[Tom_L 558]

2 hours ago, Aamir said:

Yes. It does. 

No kidding! Something with potential vs.kinetic energy probably, but what do we know? 😁