Airbus A 321 Managed/Open DES with no A/THR.
 

Good Day Everyone,

Yesterday, we were flying without auto thrust (it was U/S) and it was a new interesting experience for me. But I got a bit confused how does the FMGS works in the case you fly half manually( manual thrust control) and half managed (AP/FD ON).

For example, if you are cruising at FL 330, thrust is manually set to maintained the current managed speed and you select FL 120 and Pull OPEN DES but you intentionally don't move the thrust levers. The plane should not start descend as in OPEN DES the FD will pitch UP or Down in order to keep the speed. Right?.
Please correct me if I'm wrong.

Now we were in managed descent on the profile so the thrust levers were set to IDLE. Captain was PF and I asked him if he could put some power to see what's going to happen. He did spool up the engines and the speed went way through the upper limit of the brackets... I was a bit confused as I thought the FD will command a pitch up to stay within the speed bracket limit..

Could someone help me on this one?

Thank you. :)

Yep, top of descent if you pull for open descent and then don't close the thrust levers it will basically fly level holding the speed waiting for you to do something....Elevators controlling the speed.


During descent If you were in Managed Descent and manually increase thrust it will speed up and most likely overspeed 5 Kts ( overspeed protections ) before pitching up in normal law. It will also ask you to extend Speedbrake.

Just fly it in open descent to keep it simple, I wouldn't complicate things by using managed. Vary the V/S as required by increasing or decreasing thrust a bit.

You could select V/S to control the V/S but then you'd still need to move the thrust up or down to fly the speed you want. Elevators now controlling the V/S.

Either way, Just keep an Eye on the speed AT ALL TIMES.

ACMS beat me to it, but I just want to add one thing - do not close the thrust levers quickly when leaving TOD in OP DES...

Yes that's a good point.

No A/P!
 

Glad that you guys are told to kill the magic.
Anyway, hope you disconnect A/P when you're in OPEN DES/OPEN CLB.
Originally, this is what Airbus had edicted but then idiots started tinkering and changed procedures....
In fact, when IT was swallowed by AF, there were glaring differences in procedures and AF got its way by imposing A/THR 24/7 REGARDLESS of mode!!!
So no A/P and no A/THR in OPEN and fly like a man!!!
Tell that to you instructor!

Rubbish, who teaches that bs.

Oh I see, you are busy enough managing the speed so let's take out the autopilot as well just to increase the workload a little more.....:ugh:
Rubbish.

Have you ever flown a classic 737 or a 727 before they invented Autothrottles? Yeah they used an Autopilot that had speed hold mode and then pushed and pulled the thrust levers as required.......wow what a novel idea!! :ok:

It's not hard folks.

pineteam
In managed descent aircraft goes through repressurisation(when applicable), idle thrust and geometric segments and it will try to maintain its vertical profile. ATHR will keep changing from idle to speed mode as required to keep speed. If you were in OP DES where there is no vertical profile and added/reduced thrust the aircraft will pitch up and down to maintain speed. But in managed descent if you were on profile and added thrust the FMGC will force it down to stay on the profile so speed will increase. Nothing surprising.

Reason ?

Haven't seen any changes on that matter for the past 20 years, but maybe it's before that...

We also fly like men in RVSM airspace and congested terminal areas.

By the way April 1st is gone already

I'm with you, Winner! :D

You do realise that Winnerhofer has zero hours on anything but a keyboard and Google.

Did you fly the 146 Bloggs?

"Fly"??
 

"Fly" ? What is this strange concept of which you speak, Aeroscat? :}

Yeah, you know when you waggle that steering wheel thing to change the scenery?

Thank you for the inputs guys!!:)

@MD80rookie: What happens if you close the throttle to quickly while leaving TOD?

Thanks.

If your gross weight is low (low inertia), the plane might pitch down violently to chase speed (especially on high altitude). Not nice for the people in the back :O

Having just recently transferred to the Bus, conversion trained by highly experienced instructors, and not a word about A/P Off when OP CLB/DES. I can't see the point either. If you have MAN THR you should definitely keep A/P On to reduce workload if it's available to you.

There's nothing inherently wrong with flying AP/on, ATHR/off - PROVIDED the pilot understands and remembers he's responsible for thrust.

Colgan/BUF and Asian/SFO are examples of where the pilot failed to do that, at least as one factor.

MD80rookie
Your explanation of low inertia is very strange. Airbus FBW does not violently pitch down to capture speed. The AP maintains a steady comfortable pitch down rate that doesn't change and because of that you need to reduce thrust gradually otherwise you drop your speed. Also it is more evident at higher weight rather than lower weight.

Vilas

And that is why you should close the thrust smoothly to avoid speed loss and/or excessive pitch down. You say the same things as me but with other words, see?

MD80rookie
No, I am afraid we are not saying the same thing. Firstly I am saying opposite of what you say about the weight. Secondly when you drop the speed aircraft continues to pitch down at normal rate but gets more nose down to recover speed.That does not constitute violence. Auto pilot cannot override Load factor limit of -1g. So there is no question of any violence unless you worded it wrongly. In any case the thrust reduction has to be done controlling the trend arrow.

Vilas

Great man, try it yourself with
47 tonnes
FL350
OP DES with speed increase
Thrust Idle

The aircraft will pitch down violently to chase speed, no matter what you call it or how many arrows and Toulouse-style protections you refer to. Initially quite smoothly but once established in descend it will offer you at least -3500 fpm if you squeeze the speed up. Just like a Boeing, just like the MD did.

Looking forward to your results