Author Topic: JarDesign A320neo COMMANDED vs. MANAGED  (Read 3418 times)

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Offline Adrian Chitan

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JarDesign A320neo COMMANDED vs. MANAGED
« on: April 20, 2015, 07:58:41 AM »
Hi guys,

just wanted to quickly point out something about the JarDesign's A320neo which I've seen people usually get wrong all over the internet. They all scream about the A320 not being able to keep a good descent profile, taking care of the STAR/APP constraints, etc. Unfortunately, it has to do more with people not knowing Airbus manufacturing policy than with the actual model. Also the Aerosoft models of the A318-A321 are not accurate in this respect.

It all has to do with the difference in what Airbus calls COMMANDED vs. MANAGED.

COMMANDED

COMMANDED is the Airbus autopilot mode where the A/P is directly commanded to do something (e.g. reach an altitude, keep a speed/M#, a descent rate, etc.). If you command a descent, the A/P will put the engines on idle and descend as fast as possible also maintaining the speed that it was ordered to keep (be it a calculated speed by the computers as a function of the cost index or one that you actually ordered it to keep). It will not keep any constraint on the arrival or approach because the PILOT IS KING.

MANAGED

MANAGED mode is the Airbus autopilot mode where the A/P computes the values to be kept by using the predicted target values inserted by the pilot or the flight plan. This means that while in a descent following a STAR you will see that not only does the plane obeys speed and altitude constraints along the pathway, but it also descends at a rate that will follow the profile of the arrival/approach giving it more thrust if it needs to descend slower. This is equivalent to Boeing's automatic descend mode but it will never start by it's own.

Now, how do you go into COMMANDED or MANAGED? We will concentrate on the altitude knob because that solely takes care of the arrival and approach. Airbus employs a push and pull knob mechanism so something happens if you pull the knob and something else if you push it. To be specific, if you pull the altitude knob (hand opened on the knob before pushing the mouse button) you will put the plane in the COMMAND mode to reach that altitude. So if you COMMAND a descend the engines will go idle and the A/P will keep the speed using pitch. If you command a climb, the engines will go to full power (depending on any derate settings you've inserted and altitude/temperature conditions) and keep the speed by changing the pitch angle. That way you will get the fastest descent/climb possible with a safe flying speed. But this also means that, if you put the plane in COMMAND altitude mode while passing the T/D you will get low very fast and find yourself under the arrival profile and then have to correct this by commanding a lower descend rate. You can even help the plane into the descend by putting the speed brakes up so that the A/P has to put the nose even lower to keep the speed up.

To command a MANAGED descend, you will have to push the knob (hand closed with the index finger up before pressing the mouse button). This way, the plane will intercept and follow the descend profile of the arrival or approach with all constraints on the way. You can identify this mode by seeing speed setting limits on the speed tape as in the picture bellow.



But be aware that the limit carets will go away once in the APPROACH phase of the descent, as in the picture below.



Having a lot of experience with the JD's A320neo I can tell you that the MANAGED mode is close to perfect, following the STAR perfectly.

Cheers and I hope this helps.

Offline Bogdan Ghincea

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Re: JarDesign A320neo COMMANDED vs. MANAGED
« Reply #1 on: April 20, 2015, 12:12:22 PM »
I just started flying the Airbus X. Good tutorial on know knobe functions. I figured that has something more in it, but i didnt take the time to study it closely :)

Thanks Adrian.

 

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