PD and help + tips on Alt Rest when descending

[ap1 16]

But what i'm asking is, if i enter these alt rest 11000 and 12000 will RC des not match up with my TOD?

No, I don't think RC will match with what the TOD on the FMC says.  RC uses the general 3:1 rule I think according to Ron, so the FMC may be different.  Hope this helps.

[Driver170 42]

Are you using the 737 ngx?

 

Thanks for the reply

[ronzie 21]

It is up to you, the pilot, to manipulate the FMC attributes to match the RC altitude restriction. Whether NG or NGX or an Airbus makes no difference.

 

In a real world article I read a few months ago in Airways magazine by an airline captain, he mentioned that he always cross checked the FMC TOD against the 3:1 rule. In some cases the FMC did not correctly predict the TOD because of current conditions at the destination environment. He overrode the FMC TOD choice and was much close to a more efficient approach performance.

 

Again, RC uses the 3:1 rule for your cruising altitude to the crossing restriction to be issued, not the surface altitude.

 

I use the FS9 B737NG PMDG models and I only found a difference of ten to thirty miles, not very much for an estimated parameter at that speed and cruising altitude.

 

I monitor the descent arcs to the 40 nm range ring and if necessary inhibit VNAV and use MCP speed and V/S control to insure the arcs terminate just before the range ring.

 

When you program the FMC performance parameters and use a weather application that offers dynamic changes between departure and destination, you enter average winds aloft at cruise and predicted winds at destination (as I recall) as you conduct descent and approach. Since ground speed will vary because of immediate weather factors, the TOD on the FMC can only be an estimate anyway.

 

You might find these real-world B737 article extracts of interest:

 

http://www.b737.org.uk/rulesofthumb.htm#Approach_Profile_Planning

 

http://www.b737.org.uk/rulesofthumb.htm#Speed,_Height,_Distance_conversion and note the descent rate in the last entry in this one.

 

and the whole rulers of thumb section;

 

http://www.b737.org.uk/rulesofthumb.htm

[Driver170 42]

Hi thanks for the reply good info there ron !!!

 

But check this out my latest post

 

http://forum.avsim.net/topic/450665-fmc-reduces-flaps-up-speed-during-star/#entry3068515

 

This happened because i used that 40nm ring and leveld off at 12000 and in that time my FMC spd reduced to flaps up speed because of this temp level off while RC gives me instructions!

 

Easy solved just switch to SPD INTV

[ap1 16]

Are you using the 737 ngx?

 

Thanks for the reply.

No, I use default planes usually the default 737.  So I probably can't help you there.  But I thought I heard somewhere that RC would be different than the FMC.

[Driver170 42]

Get yourself the 737 ngx you won't look back

[ronzie 21]

No, I use default planes usually the default 737.  So I probably can't help you there.  But I thought I heard somewhere that RC would be different than the FMC.

 

As I stated in my previous post, RC uses its own estimates based on altitude difference to the crossing restriction, not surface. The FMC is your guide. RC4 ATC is your boss unless you have a safety issue where in RC you can call for a fuel emergency if you enabled hold controls in it.

 

Here's another reference about its use:

 

http://en.wikipedia.org/wiki/Rule_of_three_%28aeronautics%29

[ap1 16]

Get yourself the 737 ngx you won't look back

I know people say to always get an addon aircraft.  But I'm quite happy with the default aircraft.  I'm not really considering getting the ngx.

As I stated in my previous post, RC uses its own estimates based on altitude difference to the crossing restriction, not surface. The FMC is your guide. RC4 ATC is your boss unless you have a safety issue where in RC you can call for a fuel emergency if you enabled hold controls in it.

 

Here's another reference about its use:

 

http://en.wikipedia.org/wiki/Rule_of_three_%28aeronautics%29

I was replying to driver170.  I wasn't asking any question.

[ronzie 21]

I was just confirming that in certain phases RC could be different than the FMC. That's all.

[ap1 16]

I was just confirming that in certain phases RC could be different than the FMC. That's all.

OK, thanks.  I understand.