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Few questions regarding a320 flying (general)

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Few questions regarding a320 flying (general)

Old 27th Dec 2011, 18:44
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Join Date: Apr 2011
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Few questions regarding a320 flying (general)

Just a few general questions for the more experienced.

When activating the approach phase and descending on managed speed, and managed altitude, will the aircraft descent at thrust IDLE? Will it go at it's own pace to maintain a good rate of decent and be at an appropriate speed, allow you to slow down nicely to configure?
If ATC has not given you any specific speed, is it up to you what speed to slow down to?
Once you pull and select a speed, how can you tell before pushing back to managed speed, what speed exactly the a/c will fly in managed mode?

Also, if the ATC gives you a heading to fly outside your flight plan (selected heading), how do you get back into following your flight plan exactly?

When flying a STAR, and having it set up on the MCDU, the ATC now gives you radar vectors to intercept the Localizer.
While flying selected headings now, how exactly do you set the MCDU for this approach and cancel the STAR?

Bare with me please as I am self studying all of this.
Thank you.
z.khalid is offline  
Old 27th Dec 2011, 19:58
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Join Date: Jun 1999
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When activating the approach phase and descending on managed speed, and managed altitude, will the aircraft descent at thrust IDLE? Will it go at it's own pace to maintain a good rate of decent and be at an appropriate speed, allow you to slow down nicely to configure?
For this one take this example. Aircraft is flying a STAR followed by an approach. ATC clear you down to the platform altitude of say 3000ft. Lets say the aircraft is descending through FL120. The aircraft at this stage is in NAV and Descent mode. The managed speed target is the ECON speed computed by the FMGC. The ATHR mode will depend on where the aircraft is with regard the vertical profile. Typically the aircraft will be in Thrust Idle to maintain the descent, using speed changes in pitch to control it (you will see this speed band on the PFD). However if the aircraft should descend below the profile, the ATHR will go into speed mode and use thrust to maintain the ECON speed, and will descend at 1000 ft/min until the descent profile is regained.

As the aircraft goes through FL100 the speed will then come back to 250kts, unless deleted by the pilot. As the aircraft approaches 3000ft, there is usually a level flight segment computed by the FMGC. On the ND you will see the magenta D in a circle, which is the deceleration point, where the approach phase is automatically activated. The speed then comes back to green dot. In managed speed the speed is now controlled by the flap lever. Of course the pilot could activate the approach phase through the FMGC, however it is not necessary in managed NAV. If flying in HDG mode, the aircraft will not fly over the deceleration point therefore the pilot has to remember to activate the approach phase in the FMGC.

If ATC has not given you any specific speed, is it up to you what speed to slow down to?
It is up to the pilot, however, managed speed is recommended. However, this really depends on the circumstances. For example, if there is no speed control and say ATC have left you high, then I would use a selected speed increase to lose the altitude. But on saying that, there are many ways to skin a cat.

There are also guide lines on the speed and configuration in the airbus SOP's flying approaches.

Also, if the ATC gives you a heading to fly outside your flight plan (selected heading), how do you get back into following your flight plan exactly?
If ATC give you a heading to fly for a short time for separation, it will usually be followed by clearance to a point on the STAR. This can be achieved by using the DIR TO button on the FMGC. There are other ways too, by arming NAV mode (pushing the HDG knob) and using the radial in and out function.

When flying a STAR, and having it set up on the MCDU, the ATC now gives you radar vectors to intercept the Localizer.
While flying selected headings now, how exactly do you set the MCDU for this approach and cancel the STAR?
There are a number of ways to do this. Simply you can individually delete each way point on the STAR using the CLR key on the FMGC. Or, you could line select the centre fix of the runway on L2 this will then sequence the flight plan and automatically delete all the way points on the STAR. The other way you can do it, when you are in HDG, you could do a DIR TO the centre fix of the runway (NAV mode engages), then immediately pull HDG again, so then HDG is back on the FMA. This will in turn sequence the flight plan. It must be noted it is important to keep the flight plan sequenced, not only for accurate predictions, but when flying the approach to make sure the GA mode will be available.

Some of this stuff can be hard to understand without the simulator to play with. Of course it all comes with experience.

Hope this helps.
CAT3C AUTOLAND is offline  
Old 28th Dec 2011, 06:05
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CAT3CA,

Thank you very much for the response and help.
I do however have a few more questions if you/or anyone else doesn't mind answering.

The managed speed is not a speed I can insert into the MCDU, and want the a/c to fly once I push the speed knob correct?
It is a speed the FMGC computes I believe.
What does it base this speed on(why does it choose this speed in specific)?
Why does it choose to cruise at 250 knots when in managed speed? (for example).

Also, what is an "open descent, or closed descent"?

And "The other way you can do it, when you are in HDG, you could do a DIR TO the centre fix of the runway (NAV mode engages), then immediately pull HDG again, so then HDG is back on the FMA. This will in turn sequence the flight plan.".
I didn't quiet understand this method.
Though if I did the first method you said, deleting the waypoints on the STAR one by one, and then deleting the "flight discontinuity" now I should have my approach phase activated?
How Do I know it's activated? Is this the only time the LOC frequency / VOR or whatever approach it is will be tuned, and your final approach course set?
This is how you know your approach phase is activated?

I understand it comes with experience, but I figured reading and asking guys on here is a much better way to get myself prepared
Thanks once again!
z.khalid is offline  
Old 28th Dec 2011, 06:28
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To understand it a bit better you need to take a step back and consider "What is a managed descent?"

In laymans terms it is a descent profile, where by the FMGC has taken into account weight, wind, track miles, with speed and altitude constraints. It will actually plan a shallower profile to allow for deceleration, and allow for a steeper profile if needed.

When the approach phase is activated, it will sacrifice the vertical profile to attain its target speed, and will assume the pilot will continue to configure the aircraft to its landing configuration.

All this sounds good in theory, but practically I find it a little outside the realm of what would be considered real world profile and speed management. It does a good job, but is far from perfect.

Speed: Climb, cruise and descent speeds are specifically based on Cost Index and vary, depending on your airlines planned profiles. Essentially a trade off between time and fuel. The higher the CI, the greater the burn.

As for the 250 kt cruise. You are either below 10 000', so the airbus automatically assumes the standard speed restriction for most airspace applies unless you remove it manually.

Or your at 38000 ft or so, where you may be indicating 250 kts, but actually are targeting a specific Mach.

Open Descent, commands the ATHR to IDLE and ignores all FMGC vertical profile constraints. There is no closed Descent. You may call this a managed descent however.

May I suggest investing in a FMGC trainer and having a close looks the flight related phase of FCOM. This will help answer your question flight phase by phase

Last edited by Bula; 28th Dec 2011 at 16:17.
Bula is offline  
Old 28th Dec 2011, 09:25
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Just to add a few details to the good stuff Bula has presented.

The managed speed is not a speed I can insert into the MCDU, and want the a/c to fly once I push the speed knob correct?
First of all, and this will answer one of your other questions, the FMGC will compute your descent ECON speed based on the following factors.

Cost Index, CRZ FL, ZFW, ZFWCG, block FUEL and performance criteria.

You can actually change this speed prior to the top of descent. For example, if ATC have issued a clearance that said 'When ready descend to FL200 and on conversion maintain 280kts, you could insert this speed into the DES PERF page. The FMGC would then compute a new profile based on this speed and this would be the managed speed target. On some of the older FMGC's once the aircraft commences the descent this speed cannot be changed. However, Airbus have just released a software update to allow the pilot to change this managed speed target in the DES phase.

Why does it choose to cruise at 250 knots when in managed speed? (for example).

Also, what is an "open descent, or closed descent"?
I think Bula has answered this one for you.

And "The other way you can do it, when you are in HDG, you could do a DIR TO the centre fix of the runway (NAV mode engages), then immediately pull HDG again, so then HDG is back on the FMA. This will in turn sequence the flight plan.".
I didn't quiet understand this method.
Ok this is a little tricky to explain without an FMGC trainer. Lets say for example the STAR points are as follows.

A to B to C to D then to the Final Approach point of the ILS typically coded CR27L (27L at Heathrow).

I assume you understand that your TO way point is located on the top right hand side of the ND in white and on the second line of the MCDU? Lets say you have commenced the STAR and are flying towards point B and have 30 miles to run. If ATC then give you a heading change of 30 degrees and start to vector you around the sky for the approach. If you do nothing with the FMGC, depending on how far you are from point B, it may or may not sequence the flight plan. Therefore you could be down wind on the approach with point B behind you, maybe 30 miles or so, and the FMGC bases all its predictions of you returning back to that point, as its still your TO waypoint. Looking at the ND, because you havent deleted in way points you will see the routing in relation to position of the aircraft. You know that you are not going to go back to any waypoints on the STAR, so it is not necessary to have them displayed on the screen, plus it will give you false track mileage and false time and fuel predictions.

So, in this situation, if you did a DIR TO the CF27L the aircraft goes into NAV mode and want to fly directly to that point. However, ATC want you on a Heading. So you pull heading again to maintain your clearance. What the DIR TO has done for you, it has made the CF27L you TO way point and will automatically delete all the other way points of the STAR, i.e. point B, C and D. As you are vectored onto the localizer the aircraft will fly over the CF27L point and automatically sequence the flight plan as the aircraft flies down the approach. This is important if a missed approach is flown so NAV mode will engage.

How Do I know it's activated? Is this the only time the LOC frequency / VOR or whatever approach it is will be tuned, and your final approach course set?
This is how you know your approach phase is activated?
First of all the ILS, VOR etc will be auto tuned before the approach phase is activated. The easiest way to know if the approach phase has been activated is to press the PERF button on the FMGC. If you have not activated the approach phase prompt in blue will still be there.

Good advice from Bula too, with regard to trying to get hold of an FMGC trainer for your computer. All this stuff will become clear, as it is difficult to explain it without having a visual demonstration.
CAT3C AUTOLAND is offline  
Old 29th Dec 2011, 08:26
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Check your PM.
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