Flare mode is not correct

[dkreiskott]

Hello Jean Luc,

I reported some time ago that the flare mode is not working properly. I have now carried out several test flights and landings and noticed the same behavior each time. According to the FCOM, the A320 saves its settings at an altitude of 50 feet, then the nose is lowered to -3 degrees in 7 seconds at an altitude of 30 feet. This means that with a pitch up of 5 degrees at 50 feet, the nose is lowered by 8 degrees to -3 degrees.
The pilot must correct the pitch up himself at this moment.
But this is exactly what the A320 does not do. I have now tried it several times, for example, if you deactivate the AP at 800 feet and
no pitch change is commanded, the pitch up remains exactly as it was at 50 feet. The nose is not lowered. This is incorrect behavior. I have recorded and checked every landing.

[spaceweather]

Maybe this helps?


https://aviation.pero-online.de/wordpre ... r-landung/

[dkreiskott]

No, Peter's problem has nothing to do with the faulty flare mode.
What I mean is described in the FCOM -> Aircraft Systems -> Flight Control System -> Normal Law -> FLARE MODE.
I already wrote about this in December 2022. In the meantime, I have not seen this problem, which I have already described in this post, alone.

viewtopic.php?p=666&hilit=flare#p666
If Peter is reading along, it would be nice if he could also report here, he could also understand the problem.

[jeehell]

The flare law does NOT lower to -3°, it lowers BY 2 degrees over 8s. That means that to keep a steady pitch you need to counter the nose down moment by using some aft pitch, to simulate a conventional flare feedback.
The flare law is modeled, it is not necessarily easy to "feel" as it is subtle but it is there...

[dkreiskott]

Hello Jean Luc,

I have to disagree with you.
I was actually wrong about -3 degrees, as it is -2 degrees. But the basic description I gave is correct.
And no, the Airbus does not change the pitch by 2 degrees, but to -2 degrees.
Take a look at the picture, the text comes from the FCOM.



If you lower the Airbus by 2 degrees, the flare is implemented incorrectly.

[tcz]

Hi,

the target pitch is after 8s -2° ... so if you have at 50ft a pitch of 4°, the nose down will be 6° within 8s.
If you have a Pitch of 6° at 50ft, the nose down will be 8° within 8s.

And yes - if the Pilot not flare, the NWL will touch first

P.S. The File-Upload in the forum doesnt work ...

[dkreiskott]

Hi,

the target pitch is after 8s -2° ... so if you have at 50ft a pitch of 4°, the nose down will be 6° within 8s.
If you have a Pitch of 6° at 50ft, the nose down will be 8° within 8s.

And yes - if the Pilot not flare, the NWL will touch first

P.S. The File-Upload in the forum doesnt work ...

That's exactly what I wrote.

[jeehell]

Nope, the nose down moment will be towards ref pitch -2°.
The flare law is a actually Nz law, the NZ inputs are the pitch error (so ref target is pitch at 50ft -2°) with some gain, plus stick deflection with some gain as well, and also pitch rate with some gain. And No, you would not slam with nose wheel first. For many reasons, first being that target is NOT 2° nose down. Nobody would even want to sit in an aircraft that would try to kill you that bad ...

[tcz]

In old FCTM: " As the aircraft descend through 30 ft, the system begins to reduce the pitch attitude at a predetermined rate of 2˚ down in 8 seconds."
In newer FCTM: "As the aircraft descends through 30 ft, the system begins to reduce the pitch attitude to -2 °nose down over a period of 8 s."

So Airbus has own corrected the wording to correct explain how the system works ...
And the fixed -2° Pitch within 8 sec. make also no sense. this will be 0,25° per second - you wouldn't even notice it and you could just leave it out

[dkreiskott]

Jean Luc,
the screenshot above is from the FCOM from a real A320 pilot. Your assumption is not correct. As already written, in more recent FCOMs since 2018, the lowering of the nose to -2 degrees in 8 seconds is explicitly described.
I think a real A320 pilot knows what he is talking about.

[dkreiskott]

I have found an older FCOM. And here, too, it is written quite precisely in 2010.

...reducing it to 2 Degrees NOSE DOWN....!
My initial statement is correct.