Climb predictions on ND vs MCDU page (A320)
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Climb predictions on ND vs MCDU page (A320)
Hello guys,
Once again, I'm getting confused and frustated not to clearly undestand: Imagine you are in NAV mode, speed managed in managed climb to FL320. You must reach your cruising altitude before waypoint Bravo. But you won't make it with a managed speed of 300kt. The TOC arrow is like 15 miles ahead of the waypoint on your ND. You decided to use Vertical speed ( eg VS+2000) instead of selecting a slower speed. Now the aircraft flies rougly at 260/270kt to maintain the vertical speed. My question is: I noticed the TOC arrow on the ND was not really accurate. Like I reached FL 320 way before the actual prediction on the ND. and also the prediction on the ND (TOC arrow) and the TOC predictions on the FMS are not always exactly the same... Can someone explains please? Does the FMS predictions assume selected or managed speed only? Looks like it gets confused when using vertical speed and the actual IAS is away from for the target speed... please bring some lights on this case. Aircraft was a brand new A320 with Thales FMS.
Thank you.
Once again, I'm getting confused and frustated not to clearly undestand: Imagine you are in NAV mode, speed managed in managed climb to FL320. You must reach your cruising altitude before waypoint Bravo. But you won't make it with a managed speed of 300kt. The TOC arrow is like 15 miles ahead of the waypoint on your ND. You decided to use Vertical speed ( eg VS+2000) instead of selecting a slower speed. Now the aircraft flies rougly at 260/270kt to maintain the vertical speed. My question is: I noticed the TOC arrow on the ND was not really accurate. Like I reached FL 320 way before the actual prediction on the ND. and also the prediction on the ND (TOC arrow) and the TOC predictions on the FMS are not always exactly the same... Can someone explains please? Does the FMS predictions assume selected or managed speed only? Looks like it gets confused when using vertical speed and the actual IAS is away from for the target speed... please bring some lights on this case. Aircraft was a brand new A320 with Thales FMS.
Thank you.
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The MCDU time predictions for waypoints will be based on the climb profile and the cruise profile and it wil be the most accurate. Assuming accurate winds have been programmed.
The waypoint predictions in the top right of the ND are based on current G/S so they are not reliable for ETAs.
The Airbus TOC and descent arrows are notoriously inaccurate and are slow in updating as the vertical trajectory changes.
The waypoint predictions in the top right of the ND are based on current G/S so they are not reliable for ETAs.
The Airbus TOC and descent arrows are notoriously inaccurate and are slow in updating as the vertical trajectory changes.
Only half a speed-brake
There is a certain logic how the arrows get created. I've seen it once surely, my memory only retained the idea not to look into it again.
Various inputs are factored but not necessarily all to catch what's going on. E.g. during descent to FL 100 the arrow only indicates the point where the aircraft would have slowed down to 250 kt after reaching that level.
The scenario when climbing VS+2000, speed has dropped to 260ish and the managed target is still 290 kt, for instance, would be a one when the hockey-stick is surely meaningless.
Various inputs are factored but not necessarily all to catch what's going on. E.g. during descent to FL 100 the arrow only indicates the point where the aircraft would have slowed down to 250 kt after reaching that level.
The scenario when climbing VS+2000, speed has dropped to 260ish and the managed target is still 290 kt, for instance, would be a one when the hockey-stick is surely meaningless.
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pineteam
Unfortunately in FCOM the words of wisdom are scattered in many places so it becomes difficult to fully understand a system especially like the auto flight. This is what I found in one place.
Unfortunately in FCOM the words of wisdom are scattered in many places so it becomes difficult to fully understand a system especially like the auto flight. This is what I found in one place.
The flight crew should rely on the ND for short-term predictions. It indicates what the aircraft will do under the currently engaged modes (selected or managed). The flight crew should rely on the MCDU for long-term predictions, when managed guidance is active or about to be reengaged.
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Thank you for your answers guys.
Vilas, thank you. I read that also. Not much from the Fcom..
I tried Yesterday quickly during climb. I pull V/S: +2000 ( it was in CLB with a VS of about 1100') And the TOC arrow on the ND moved backward and the distance to TOC was pretty accurate. On the MCDU performance page on the other hand, the TOC distance remained unchanged.
I don't want to open a new debate. I heard that so many times during line training. I do agree at high altitude on an heavy aircraft with tigh buffet margin, definetely not a good idea. But when you still below FL300 in smooth condition, using vertical speed is not a problem as long as you monitor carefully your PFD. Just keep a safe margin from GD speed. I quite like it actually especially when you have to reach an altitude in a certain distance or time.. If I set 1000'/min passing Fl220 climbing Fl320, I know in 10 min exactly I will be at Fl320. Add 1 or 2 min for safe margin in case you will need to reduce it to keep speed above VLS. Cause in Manage speed at 300kt+ how many times the plane pitch up and down to maintain the speed and V/S often falls close to zero. Kinda annoying. = )
Vilas, thank you. I read that also. Not much from the Fcom..
I tried Yesterday quickly during climb. I pull V/S: +2000 ( it was in CLB with a VS of about 1100') And the TOC arrow on the ND moved backward and the distance to TOC was pretty accurate. On the MCDU performance page on the other hand, the TOC distance remained unchanged.
I don't want to open a new debate. I heard that so many times during line training. I do agree at high altitude on an heavy aircraft with tigh buffet margin, definetely not a good idea. But when you still below FL300 in smooth condition, using vertical speed is not a problem as long as you monitor carefully your PFD. Just keep a safe margin from GD speed. I quite like it actually especially when you have to reach an altitude in a certain distance or time.. If I set 1000'/min passing Fl220 climbing Fl320, I know in 10 min exactly I will be at Fl320. Add 1 or 2 min for safe margin in case you will need to reduce it to keep speed above VLS. Cause in Manage speed at 300kt+ how many times the plane pitch up and down to maintain the speed and V/S often falls close to zero. Kinda annoying. = )
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@pineteam
i'm not even a pilot but as far as i understand you should look up your Vx (best climb angle speed) if you are concerned about reaching a level. don't know if it's as low as VLS but i doubt it somehow.
going below Vx would be very uneconomical and reduce your V/S. autopilot would then pitch up further to keep the V/S and you only reduce it reaching VLS meaning you are wasting fuel and not even achieving your max angle of climb.
but i guess you normally set your V/S trying to keep it near your managed speed and not even going close to Vx or VLS.
i'm not even a pilot but as far as i understand you should look up your Vx (best climb angle speed) if you are concerned about reaching a level. don't know if it's as low as VLS but i doubt it somehow.
going below Vx would be very uneconomical and reduce your V/S. autopilot would then pitch up further to keep the V/S and you only reduce it reaching VLS meaning you are wasting fuel and not even achieving your max angle of climb.
but i guess you normally set your V/S trying to keep it near your managed speed and not even going close to Vx or VLS.
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Vx for Jet aircraft is around (at?) minimum clean speed(green dot). Especially when the AC is heavier, VLS can be at green dot.
Note that Vx and Vy are very different from prop to jet AC.
Gotta love the guys that are afraid of using V/S on the bus... I don't really think the constant pitch changes are very comfortable.
Note that Vx and Vy are very different from prop to jet AC.
Gotta love the guys that are afraid of using V/S on the bus... I don't really think the constant pitch changes are very comfortable.
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That was during my line training as fo when I did not know anything about Airbus. I never argued with any instructors or any line captains. My training went smooth thank you. I'm now captain and Instructors with common sense will never say anything if I'm using V/S during climb when the buffet margin is wide. I'm a pilot not a robot. I use the automation and all the tools Airbus has to offer while fully undestanding the consequence if something goes wrong. Yes using Climb mode is safer but does not mean using vertical speed is dangerous.
Oh my god thank you. At least one guy to support me. Tired of people afraid to fly close to VLS or green dot speed. If you inadvertently goes into VLS you won't die, you will have a reversion mode. You don't have to do anything. Lol. Gotta love the guys also afraid to use expedite mode at low altitude cause the target speed is Green dot. Funny how those people forget than when they are flying in the sim on single engine they fly at green dot speed....
Oh my god thank you. At least one guy to support me. Tired of people afraid to fly close to VLS or green dot speed. If you inadvertently goes into VLS you won't die, you will have a reversion mode. You don't have to do anything. Lol. Gotta love the guys also afraid to use expedite mode at low altitude cause the target speed is Green dot. Funny how those people forget than when they are flying in the sim on single engine they fly at green dot speed....
Last edited by pineteam; 21st Aug 2017 at 12:35.
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using vertical speed is not a problem as long as you monitor carefully your PFD. Just keep a safe margin from GD speed.
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What do you know about my experience? Air Macau is not my first aviation job. Don't judge a book by his cover. Since now my thread is spoiled, I'm happy to listen to your concern about using vertical speed during climb. Maybe you can write to Airbus also cause as far as I'm aware it's not written in the Fcom or Fctm that using vertical speed is dangerous.
And I have flown with captains who fly Airbus for 10 years + and I won't trust them to fly my family. That's how bad they are. Just because they fly for a long time does not mean they are amazing pilots...
Vilas if you read this I would like to have your opinion also since you are a master on Airbus.
And I have flown with captains who fly Airbus for 10 years + and I won't trust them to fly my family. That's how bad they are. Just because they fly for a long time does not mean they are amazing pilots...
Vilas if you read this I would like to have your opinion also since you are a master on Airbus.
Last edited by pineteam; 21st Aug 2017 at 13:47.
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Give me a break man. You have 
to say such a thing when you are the one who come on my thread and said that Vertical speed should not be used. Where do you get that from? From some captains who don't know what VLS means? Nowhere in the Fcom or Fctm there is a restriction about it. So check your sources before insulting Air Macau and I. The questions I asked are usually not written in Airbus manuals or are ambiguous. I do study a lot before asking questions here. I'm very far from knowing everything but I try my best to improve my knowledge. And it does not hurt to ask questions on Pprune. Lots of guys here like Vilas and Open Des and many others are very knowledgeable and I really like hearing from their experiences. It's with this attitude that I managed to get upgraded so quickly with no previous jet time experience.
to say such a thing when you are the one who come on my thread and said that Vertical speed should not be used. Where do you get that from? From some captains who don't know what VLS means? Nowhere in the Fcom or Fctm there is a restriction about it. So check your sources before insulting Air Macau and I. The questions I asked are usually not written in Airbus manuals or are ambiguous. I do study a lot before asking questions here. I'm very far from knowing everything but I try my best to improve my knowledge. And it does not hurt to ask questions on Pprune. Lots of guys here like Vilas and Open Des and many others are very knowledgeable and I really like hearing from their experiences. It's with this attitude that I managed to get upgraded so quickly with no previous jet time experience.
Last edited by pineteam; 22nd Aug 2017 at 07:34.
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It's with this attitude that I managed to get upgraded so quickly with no previous jet time experience.
Air Macau is still off my list. If it's not good enough for your family, it's not good enough for me.
And I have flown with captains who fly Airbus for 10 years + and I won't trust them to fly my family. That's how bad they are. Just because they fly for a long time does not mean they are amazing pilots...
Vilas if you read this I would like to have your opinion also since you are a master on Airbus.
Vilas if you read this I would like to have your opinion also since you are a master on Airbus.
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I joined Air Macau with 1900hr PIC... And was upgraded with 4500hr total time including 2000hr+ on type. What more do you need to be confortable on an aircraft?
Concerning the bad pilots, they are everywhere... You should open more your eyes and maybe the FCOM also. Please stop trolling my thread. Thank you.
Concerning the bad pilots, they are everywhere... You should open more your eyes and maybe the FCOM also. Please stop trolling my thread. Thank you.
Last edited by pineteam; 22nd Aug 2017 at 12:28.
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pineteam
First the VS mode. Nothing is forbidden off course but some things are recommended. Aversion to VS mode may have it's origin in the fact that in VS mode the speed(global as it is called) protection is a later development and wasn't their from the beginning. Secondly the priority of this mode is VS and not speed so sometimes not an appropriate mode.
As far as command upgrades are concerned there is regulatory minimum, beyond that it is on requirement. Without proper attitude and aptitude mere thickness of logbook is like growing old it just happens. Experience can be what Oscar wilde had said "Experience is merely the name men gave to their mistakes".
First the VS mode. Nothing is forbidden off course but some things are recommended. Aversion to VS mode may have it's origin in the fact that in VS mode the speed(global as it is called) protection is a later development and wasn't their from the beginning. Secondly the priority of this mode is VS and not speed so sometimes not an appropriate mode.
As far as command upgrades are concerned there is regulatory minimum, beyond that it is on requirement. Without proper attitude and aptitude mere thickness of logbook is like growing old it just happens. Experience can be what Oscar wilde had said "Experience is merely the name men gave to their mistakes".
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Agreed Vilas
V/S (very seldom as we like to say) mode use by the PF increases the PM work load. I can count a dozen times where the PF (FO in my case) has used that mode and forgot to monitor the airspeed - in a climb and/or descent. I have seen pilots use it incorrectly in managed climb and descent WRT appropriate altitude set in the FCU. I have occasionally seen incorrect use of speed brakes with V/S which results in a discussion of what V/S is and is not.
At some airports noise requirements may necessitate use of V/S to maintain a constant descent, some descents may require the use of V/S but personally, I don't believe V/S is an appropriate mode in most cases - my opinion only - not procedure.
V/S (very seldom as we like to say) mode use by the PF increases the PM work load. I can count a dozen times where the PF (FO in my case) has used that mode and forgot to monitor the airspeed - in a climb and/or descent. I have seen pilots use it incorrectly in managed climb and descent WRT appropriate altitude set in the FCU. I have occasionally seen incorrect use of speed brakes with V/S which results in a discussion of what V/S is and is not.
At some airports noise requirements may necessitate use of V/S to maintain a constant descent, some descents may require the use of V/S but personally, I don't believe V/S is an appropriate mode in most cases - my opinion only - not procedure.
