A320 Fcom 1.22.30 P12 Speed/mach Switching
Thread Starter
Joined: Mar 2005
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From: Uh... Where was I?
A320 Fcom 1.22.30 P12 Speed/mach Switching
I confess I don't fully understand when and why the selected speed target switches to mach target (or the opposite in descent).
When speed is managed I understand that, as there is a known speed/mach schedule, the FMGC knows what the crossover altitude is, and changes over exactly at the crossover altitude. Am I correct?
In selected speed, however, the FMGC doesn't know what our plans are for the climb (or descent), so it switches to mach (or speed) at a FL according to the table in this paragraph. Am I correct? For a given climb IAS there is a given mach number and a crossover FL? And for a given descend mach number there is a given IAS and a given crossover FL? If so, I don't know very well how to read that table.
For instance, climbing at 300 kt, What will occur? switch to 0.76 at FL265 always?
And what about descending at 0.76? will the target switch to 280 kt at FL305always?
What about climb speeds lower than 280? Is it that at any speed lower than that the switching will occur always at FL305, whatever the actual mach number?
And what about descending mach numbers lower that 0.76? Is it that at any mach lower than that the switching will occur always at FL 305 no matter what the IAS?
thanks
When speed is managed I understand that, as there is a known speed/mach schedule, the FMGC knows what the crossover altitude is, and changes over exactly at the crossover altitude. Am I correct?
In selected speed, however, the FMGC doesn't know what our plans are for the climb (or descent), so it switches to mach (or speed) at a FL according to the table in this paragraph. Am I correct? For a given climb IAS there is a given mach number and a crossover FL? And for a given descend mach number there is a given IAS and a given crossover FL? If so, I don't know very well how to read that table.
For instance, climbing at 300 kt, What will occur? switch to 0.76 at FL265 always?
And what about descending at 0.76? will the target switch to 280 kt at FL305always?
What about climb speeds lower than 280? Is it that at any speed lower than that the switching will occur always at FL305, whatever the actual mach number?
And what about descending mach numbers lower that 0.76? Is it that at any mach lower than that the switching will occur always at FL 305 no matter what the IAS?
thanks
Joined: Oct 2009
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From: UK
Hi, I've found a similar table and agree with your changeover assumptions. The table does not seem to be complete. I'm assuming the "Crossed Box" is missing at FL315 and above the 280 kts /.76 column.
I'll investigate your .75 descent changeover FL and your 270 kts climb next chance I get.
I find Airbus is poor at providing information for pilots, it's almost as if they attempted to design the pilot out of the flight deck.
Rgds rudderrudderrat
I'll investigate your .75 descent changeover FL and your 270 kts climb next chance I get.
I find Airbus is poor at providing information for pilots, it's almost as if they attempted to design the pilot out of the flight deck.
Rgds rudderrudderrat
Joined: May 2000
Posts: 1,021
Likes: 2
From: Glorious West Sussex
Had you bothered to search you would have found this...
http://www.pprune.org/tech-log/37496...switching.html
http://www.pprune.org/tech-log/37496...switching.html
Joined: May 2000
Posts: 1,021
Likes: 2
From: Glorious West Sussex
M2002
Do you need to understand? Why not just fly the aeroplane? You have chosen to use SEL SPD for a reason - just monitor the a/c and if you don't like the IAS or M after changeover then adjust it!
What difference would it make if there was no table?
I confess I don't fully understand when and why the selected speed target switches to mach target
What difference would it make if there was no table?
Thread Starter
Joined: Mar 2005
Posts: 1,338
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From: Uh... Where was I?
Yes, of course.
Climb and cruise mach number is the same most of the times for a given company CI, so all we have to do is switch the reference to Mach number manually when this particular mach number is reached, or switch back to speed if the FMGC switches it on its own before reaching it.
It is only I would like to know exactly how the system works. I don't like seeing a table in the FCOM that I don't know how to interpret.
Climb and cruise mach number is the same most of the times for a given company CI, so all we have to do is switch the reference to Mach number manually when this particular mach number is reached, or switch back to speed if the FMGC switches it on its own before reaching it.
It is only I would like to know exactly how the system works. I don't like seeing a table in the FCOM that I don't know how to interpret.
