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CRZ Level Mach Resetting

 
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Tankleader



Joined: 23 Dec 2016
Posts: 29

PostPosted: Mon Oct 21, 2019 9:34 am    Post subject: CRZ Level Mach Resetting Reply with quote

Hello,

The Cruise MACH number resets on FMC VNAV CRZ page anytime there is a change in altitude to a higher level.

During the programming for the flight the mach number on the INT REF page can be set to .84, but this changes during the climb phase to match the CLMB Speed and mach. This wasn't happening before. I can change the mach to .84 again and it will hold..
Thanks

Andy Elesky
1.96
P3D4.5
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MarkHastings



Joined: 18 Jan 2006
Posts: 933
Location: UK

PostPosted: Tue Oct 22, 2019 6:23 am    Post subject: Reply with quote

I'm unclear on your question ?

Quote:
During the programming for the flight the mach number on the INT REF page can be set to .84

You don't set the MACH number on the INIT REF page. Do you mean the COST INDEX ?

Entering a new CRZ altitude will trigger a recalculation of the VNAV speeds based on your entered cost index.

The MACH is dependent on the CRZ Altitude as the speed is converted to a mach number...
ie
CI : 100
FL150
CLB Speed = 302
CLB Mach = 0.597

FL350
CLB Speed = 302
CLB Mach = 0.800

In the AIRLINE POLICY you can 'Bias' the cost index.
On the Ground : INIT REF > INDEX > MAINT >AIRLINE POLICY > Page 2 > "Cost Index Bias"

eg : Setting the Bias = 200 will have the affect of pushing the speeds up for a lower entered cost index.
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Mark Hastings
Software Developer
Sim-Avionics
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Tankleader



Joined: 23 Dec 2016
Posts: 29

PostPosted: Tue Oct 22, 2019 6:52 am    Post subject: CRZ Level Mach Resetting Reply with quote

Mark,
Thanks for the information and clarification. I've noticed that my speeds have been lower since updating to 1.96 based on my cost index, but I may be imaging things since I am trying to pay more attention to what I am doing.

Thanks
Andy
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