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

[pineteam]

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. :)

[ACMS]

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.

[MD80rookie]

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...

[ACMS]

Yes that's a good point.

[Winnerhofer]

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!

[ACMS]

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.

[vilas]

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.

[sonicbum]

Glad that you guys are told to kill the magic.
Anyway, hope you disconnect A/P when you're in OPEN DES/OPEN CLB.

Reason ?

Originally, this is what Airbus had edicted but then idiots started tinkering and changed procedures....

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

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!

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

By the way April 1st is gone already

[Capn Bloggs]

I'm with you, Winner! :D

[KBPsen]

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

[AerocatS2A]

I'm with you, Winner! :D

Did you fly the 146 Bloggs?

[Capn Bloggs]

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

[AerocatS2A]

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

[pineteam]

Thank you for the inputs guys!!:)

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

Thanks.

[MD80rookie]

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

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.

[pattern_is_full]

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.

[vilas]

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.

[MD80rookie]

Vilas

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.

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?

[vilas]

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.

[MD80rookie]

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

[vilas]

MD80rookie
I don't have to try. I have seen it and already know. If you had used the correct terminology this discussion was not required. What you meant was that the aircraft will enter steep descent to capture the speed. Isn't that what it is supposed to do? But it will still do it at -1G and not violently. While reducing thrust if you ensure that negative large trend vector does not develop then the situation is no different than with ATHR on. And I never heard this phrase Toulouse style protection. Steep descent and high negative G are not same.

[capt. solipsist]

Too bad the new FCOM versions did away with the FCBulletins.

But if you still got access to them, a bulletin states that, with the FADEC working, the fastest rate of thrust reduction the FADEC would allow is 1% PER SECOND.

Meaning, even if you close the thrust levers at the speed of light, thrust reduction would still go no faster than 1% per second.

That's why I don't get all this concern re Open Des. :ugh:

[hikoushi]

Regarding the "violent" pitching.

I have seen (from the jump seat) an A330, fully autopilot coupled, pitch itself down into its own "pitch attitude protection" limit in OP DES. This was due to the captain pulling open descent at Mach .82 at 41,000 feet and descending from a 100-ish knot headwind into a 50-ish knot tailwind through a fairly tight shear layer. The thing just couldn't catch the speed target, as it kept creeping up the tape while the actual airspeed was affected by the tailwind shear.

The vertical rate got to about 7000 FPM (indicator turns yellow) down within a matter of about 10 seconds, and the pitch dropped below 12 degrees. As the plane went thru another shear layer, the pitch touched the green hash marks and started to immediately rise. This of course made the speed drop, causing the airplane to pitch down again, etc etc etc.

The whole process here took less than 20 seconds. It took the operating crew that long to respond to my corrective callout. Why? They were busy looking out the window for traffic to follow, while complying with a descent clearance. The autopilot was so amazingly smooth that they simply did not notice until it was diving like a homesick brick. Nighttime with no moon, no horizon outside to reference.

Both of your comments, in other words are true.

Moral? In normal situations don't pull open descent at FL410 if you are descending into a tailwind / quickly weakening headwind.

[sonicbum]

Moral? In normal situations don't pull open descent at FL410 if you are descending into a tailwind / quickly weakening headwind.

It is not forbidden to adjust the speed in such a way that your pitch and ROD will stay within acceptable limits or as you suggest revert to V/S. The point is that whatever the crew decides, the airplane flight path must be monitored. Having 2 pilots looking out the window means that nobody is flying the airplane.

[vilas]

Moral? In normal situations don't pull open descent at FL410 if you are descending into a tailwind / quickly weakening headwind.
Firstly when 100kts. head wind turns into 50kts. tail wind it is not normal. It is a serious wind shear and what happened is not unusual. It could have been worse as it could have tripped the auto pilot or triggered alpha protection. It has happened before. So open descent is not the cause. Secondly the original topic by MD80 was manually reducing the thrust quickly in open descent, which obviously one shouldn't and aircraft pitching down steeply to regain lost speed which it should. If the thrust is reduced as auto thrust does then there is no problem. My point is AB FBW may pitch down to whatever degrees but it will do so at 1G, you can call it a steep descent and want to avoid it, that is fine. Toulouse style protections is another mystery, may be he is repeating a phrase by one of his experienced Airbus sceptical instructors because by his own admission he is a neophyte to the bus.

[hikoushi]

All true. I can only assume that slamming the throttles to idle in a similar situation would make it even worse.

Not a typical wind to be sure, but have seen it come pretty close more than once descending out of a jet core landing in the tropical Pacific. Shear layer about 5-10,000 feet thick, well below the high tropopause typical of the latitude. Hence "chasing the Mach" in the descent. Seen the "open descent Mach dive" more than once, usually with inexperienced crews. They usually catch it right away.

A managed descent in managed speed, with a good wind profile inserted, makes the whole thing a total non-issue.

[Winnerhofer]

On the MD-80 we sometimes flew high at the edge of the aircraft’s performance envelope (in those days the performance tables and aircraft weight were not so exact) and encountered buffeting in turns with more than 10° bank.
If you entered the top layer of a thunderstorm in such conditions, you could lose lift rapidly and disappear in the cloud.
In 2006 I flew a heavy A321-200 above its maximum recommended flightlevel to get over a thunderstorm.
With open climb mode I anticipated a slow climb.
Checking the primary flight display it showed an unexpected ROC of 3,500ft/min with rapidly decreasing airspeed.
What happened?
The computer extrapolated that beyond normal range the aircraft would not be able to fly high and fast simultaneously, and reduced speed to M.73 by itself.
To get there from M.79 it pitched up to a ROC irrationally high in thin air.
It would have meant stalling and falling into an active storm.
The A321 software may be updated to avoid this condition but it shows the vigilance needed at the edge of its performance envelope.
A computer-controlled aircraft is still only an aerodynamic machine.

[sonicbum]

Winner rather than the technical aspect of the airplane I would consider the fact that climbing above REC MAX to get over a thunderstorm can lead to some serious headaches.

[vilas]

Heavy aircraft, on top of thunderstorm and above REC MAX you were lining up the swiss cheese holes. Why is that?

[Field In Sight]

I'm pretty sure it didn't change the speed to increase the climb rate.
Speed is only changed to adjust flight path in the descent.

Possibly the aircraft entered an area of significant temperature difference and the econ climb speed changed.

[Uplinker]

Errr, Winnerhofer. Why were you trying to fly OVER a thunderstorm at your level????

And why did you talk about flying THROUGH the top of a thunderstorm in a previous post???

Dude, you must go AROUND thunderstorms, and stay at least 20 nm away from them, and on the upwind side. They are bloody dangerous.

Perhaps you should dig out your meterology notes and refresh your memory.

[jdawg]

winnehofer
I am glad you are here to speak with us today.
Exceeding REC MAX in any situation is foolish and unprofessional.
To do so on top of an active storm is gravely ignorant.
Above and below storms are both very dangerous places, upwind is the place to operate.

[whitelabel]

47 T seem very light but ok. Pitch is LF in the airbus during flight in normal law. I never tried your technique but what I suspect is that when you immediately cut the power the pitch will adjust gradually. Initially leading to a slight underspeed and then with a high ROD catching up with the speed and probably leading to a slight overspeed again. You sometimes see it in an open climb as well. Very high roc to maintain the speed and then you lose all your v/s because it now underspeeds by >10kts. At high altitude in climb i prefer use of V/S exactly to avoid an underspeed due to large vsi changes

[PlanetEarth]

If this Winner guy is not a troll, I really worry for his passengers

[Bengerman]

Also, if descending from high level with a Mach in OP DES the speed will increase as a natural function of Mach vs airspeed.
I have seen >7000'/min descent often in A318, all normal if a little unsettling.