Speed instruction mach convertion speed

I was given an instruction by a controller speed mac 0,85 conversion .speed… I do not recal precisely.
I guess I have to change from mach to knots at a certain altitude of my descent but I do not understand How to apply this precisely.
Can somebody help me ?

As you descend your IAS will increase if you maintain a certain mach number.

The instruction wants you to maintain mach .85 until that is equal to an IAS of X, and to maintain speed X from that point onwards.

Hi Patrick,

exactly as Lars has described it. If you use an aircraft with a sophisticated FMS, you could modify the speeds in its PERFORMANCE section on the DESCENT page. This way you can continue using VNAV if you wish.

What plane(s) and SIM-platform do you usually use, are they complex enough to do this?

Thanks to both of you
I am using XP11 TOLISS A321 and A 346 which are perfectly able to do this
So if If I am instructed fly mach .85 conversion 320 kts, I manage mach .85 on the MCP and when I reach 320 on the PFD I switch from mach to kts on the MCP.
Is this correct understanding ?

Yes, correct. And you can also play around in the MCDU’s DESCENT-page and change the numbers there, if you wish to continue using VNAV during descent.

ah yes I had forgotten this way of proceeding with MCDU DESCENT page , but here is it Mach or IAS kts speed that you modify ?

Maybe both, depending on the instruction. If your VNAV Mach number is different from the one that ATC has instructed you, then you will need to modify the Mach and the IAS on the DESCENT page, if possible. But if it gets too much and takes too much time, just do it is as Lars wrote: use “selected MACH/SPEED” first, then modify the DESCENT page and try if “managed MACH/SPEED” will work as expected. With just one person in the virtual cockpit, the workload can become quite high in such situations. Even IRL we will probably first set the requested Mach number or IAS manually and then only start re-programming the FMS speed profile.

Yes it is a lot of work for a single pilot.
I will check this in flight.
Once again thanks a lot to both of you for your professional support,

No problem. In the real world it is just a question of routine and practice. Once you have done such settings a few times, it will be done rather quickly from then on. So, practice, practice, practice.

Thanks I have been joining VATSIM recently and it is sometimes difficult especially when you get a late descent clearance even using speedbrakes with speed restrictions. This is my main difficulty with VATSIM controllers !

You are free to request descent a bit earlier. But please not too early, otherwise ATCOs may think that you have no idea of what you are doing :smiley: I sometimes encounter pilots requesting descent 200 NM before their destination, which is hardly realistic.

I am not requesting descent too early , I have my TOD and my profile easily readable with Toliss Airbuses.
Today I was with Barcelona center I asked several times to continue my descent but the controllers did not let me descent from FL 250, he transferred me to Ibiza approach at this Fl, and with a speed restriction at 250 kts, thus I was 11000 ft above the descent profile ! Even with speed brakes impossible to catch up the descent profile and respect the speed restriction, I explained Ibiza approach I was anable to comply with the STAR descent profile, this controllers understood my situation and offered me vectoring with extra mileage to catch up the descent profile to the ILS. I was very stressed. Sometimes I wonder if ATC controllers understand how to pilot a jet ! I have speedbrakes , not a parachute.!
I have less than 10 flights with VATSIM and progressing with every flight. But sometimes it is very difficult and stressing. Most controllers are nice and comprehensives, but some are agressive.

98% of our members are hobbyists and may make “simple” mistakes. Nobody’s perfect. Even us IRL guys make mistakes, every single day. Such is life.

Yes this for sure.
Was just explaining my difficulties in the learning curve.
Have a good week.

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