Jump to content

Sign in to follow this  
threegreen

CI and STAR speed restrictions

Recommended Posts

I usually use a CI of 10 or something similar and get a descent speed of 250 kts. Depending on the arrival airport and the STAR I then get the message e.g. 'unable 280kts at XXX'. I just put in 250 kts or whatever my descent speed is instead of what the STAR tells me to do. I'm wondering how this is done in RW?


Prepar3Dv5 | ASUS Maximus XI Code Z390 | i9 9900K 5 GHz | Corsair Vengeance RGB Pro 32 GB DDR4 3600 MHz | GeForce RTX 2080 Ti 11 GB GDDR6 MSI Lightning Z Windows 10 Pro 64 bit | Samsung 850 EVO 1 TB | Samsung 43'' 4K curved TV | HP Reverb 2 VR HMD | Agronn 737 Captain's Yoke | FSC 737 Throttle Quadrant | Saitek Pro Flight Rudder Pedals

 

Share this post


Link to post
Share on other sites

Why?

If you listed to the traffic, you'll find most descent speeds are 280, 290 or 310 depending on location...., I've never see a 250 descent restriction above say 140 or so. 

Selecting a CI based on the descent speed is very interesting approach. However, it indicates that maybe you should do some reading about the reason we use CI.

In the NGX, I may use a CI of 25-35 for low cost and 80 in my BBJ where time is money.  Regardless, I usually adjust the descent speeds to match the arrival and location.


Dan Downs KCRP

Share this post


Link to post
Share on other sites

It's telling you it can't comply with the speed constraints on the arrival.  The usual cause is the speed on the VNAV descent speed is lower than the speed constraint on the legs page.  To comply with the arrival speeds you need to put a high enough speed on the descent page.


Joe Diamond

Share this post


Link to post
Share on other sites
6 hours ago, downscc said:

Selecting a CI based on the descent speed is very interesting approach. However, it indicates that maybe you should do some reading about the reason we use CI.

Don't believe that's what he meant.

6 hours ago, Canuck said:

I usually use a CI of 10 or something similar and get a descent speed of 250 kts.

I took that to mean that the descent speed of 250 was a result of using a cost index of 10 rather than him deliberately selecting the cost index to get that speed.

  • Upvote 1

Captain Kevin

8e9bfe368edaef204bfa6a1373fc6422.jpg

Air Kevin 124 heavy, wind calm, runway 4 left, cleared for take-off.

Live streams of my flights here.

Share this post


Link to post
Share on other sites

RW would use the cost index based on the airlines SOP and dispatch.  It's adjusted for time and fuel.  In the real world for descent you would comply with ATC.  If they tell you to keep your speed up to 290 or faster, than that's what you'd do for traffic spacing.  A STAR is more reference than anything but is closer to the speed used at higher altitudes.  One plane can throw this off though.  Same with the fact that a lot of ATC will divert you off the STAR for vectors at some point.  

To be realistic but within the confines of the sim, just stay at 280. So if your descent page above 10,000 says 250 (too slow above 10,000 btw) than change it to 280.  I used 32 most often but that gives me 275 above 10,000 so I get that message.  Either I change it on the descent page or legs page (if it's just one hard restriction waypoint).  Keep in mind it's not uncommon to have to open the speed window and alter it that way.  It's not like there's a right or wrong way to maintain the proper speed. 


- Chris Jefferies

 

Asus Maximus VII Hero motherboard | Intel i7 4790k CPU | MSI GTX 970 4 GB video card | Corsair DDR3 2133 32GB SDRAM | Corsair H50 water cooler | Samsung 850 EVO 250GB SSD (2) | EVGA 1000 watt PSU

Share this post


Link to post
Share on other sites

At my company, we use 250/280.78 for climb and descent. CI for cruise. Over-write the descent from CI with something that makes sense.


Matt Cee

Share this post


Link to post
Share on other sites
20 hours ago, downscc said:

Why?

If you listed to the traffic, you'll find most descent speeds are 280, 290 or 310 depending on location...., I've never see a 250 descent restriction above say 140 or so. 

Selecting a CI based on the descent speed is very interesting approach. However, it indicates that maybe you should do some reading about the reason we use CI.

In the NGX, I may use a CI of 25-35 for low cost and 80 in my BBJ where time is money.  Regardless, I usually adjust the descent speeds to match the arrival and location.

What Kevin said. I know what CI does, the 250kts are just a result of me putting in a CI of 10 because it's what the RW counterpart of my VA uses most of the time.

 

10 hours ago, Orlaam said:

RW would use the cost index based on the airlines SOP and dispatch.  It's adjusted for time and fuel.  In the real world for descent you would comply with ATC.  If they tell you to keep your speed up to 290 or faster, than that's what you'd do for traffic spacing.  A STAR is more reference than anything but is closer to the speed used at higher altitudes.  One plane can throw this off though.  Same with the fact that a lot of ATC will divert you off the STAR for vectors at some point.  

To be realistic but within the confines of the sim, just stay at 280. So if your descent page above 10,000 says 250 (too slow above 10,000 btw) than change it to 280.  I used 32 most often but that gives me 275 above 10,000 so I get that message.  Either I change it on the descent page or legs page (if it's just one hard restriction waypoint).  Keep in mind it's not uncommon to have to open the speed window and alter it that way.  It's not like there's a right or wrong way to maintain the proper speed. 

Native ATC is the problem here. I tried both ProATC X and PF3 but didn't like either for performance and reliability reasons so I went back to P3D/FSX ATC which isn't as realistic, obviously, but still more reliable. So I rely more on the FMC's speeds and STAR/SID procedures than in RW.

 

9 hours ago, Spin737 said:

At my company, we use 250/280.78 for climb and descent. CI for cruise. Over-write the descent from CI with something that makes sense.

I always used the speeds that were calculated by the FMC with the information I put in because I took the 'don't mess with it, it's more intelligent than me' approach and thought I would mess the descent profile up when changing speeds manually.


Prepar3Dv5 | ASUS Maximus XI Code Z390 | i9 9900K 5 GHz | Corsair Vengeance RGB Pro 32 GB DDR4 3600 MHz | GeForce RTX 2080 Ti 11 GB GDDR6 MSI Lightning Z Windows 10 Pro 64 bit | Samsung 850 EVO 1 TB | Samsung 43'' 4K curved TV | HP Reverb 2 VR HMD | Agronn 737 Captain's Yoke | FSC 737 Throttle Quadrant | Saitek Pro Flight Rudder Pedals

 

Share this post


Link to post
Share on other sites

In my experience speeds on SIDs/STARs are usually maximum speeds. In these days of low CIs, long, slow descents are quite par for the course and if you are below the speed in question you should not have too many issues. If ATC require a particular speed they will ask you.

To quote from a real-world Eurocontrol ATCO on another forum I am a member of:

Quote

We are very used to different aircraft flying different speeds and have the ability to deal with this when controlling the traffic flow

 


Simon Kelsey

sig_FSLBetaTester.jpg

 

Share this post


Link to post
Share on other sites

Ok but you asked about RW procedures.  What the RW operator uses is irrelevant to speed profiles as stated on a chart or the FMC.  RW ATC will usually ask for speed changes if needed.  Speeds are overridden all the time anyhow for a myriad of reasons.  

The concept of relying on MS ATC or a 3rd party ATC is worthless.  It takes no consideration for speed and is anything but realistic.  

Don't worry about messing with the speed in the FMC. It recalculates as it's updated.  


- Chris Jefferies

 

Asus Maximus VII Hero motherboard | Intel i7 4790k CPU | MSI GTX 970 4 GB video card | Corsair DDR3 2133 32GB SDRAM | Corsair H50 water cooler | Samsung 850 EVO 250GB SSD (2) | EVGA 1000 watt PSU

Share this post


Link to post
Share on other sites
21 hours ago, Canuck said:

I'm wondering how this is done in RW?

As the others noted, you did it a bit in the reverse. Overwrite the speed on the descent page (ideally prior to T/D) using the STAR restriction.


Kyle Rodgers

Share this post


Link to post
Share on other sites

And actually that reminds me - on this topic:

36 minutes ago, Canuck said:

I always used the speeds that were calculated by the FMC with the information I put in because I took the 'don't mess with it, it's more intelligent than me' approach and thought I would mess the descent profile up when changing speeds manually.

Two main points:

First -- you over-estimate the FMC's capabilities :biggrin:. They are not bad, but they are still pretty dumb computers and the main thing computers cannot do is anticipate. Most of the time a human pilot can do a much more efficient job :wink:.

Second -- your point about the descent profile is a good one. As a general rule, the FMC will calculate the profile based on the speed in the VNAV DES page.

If you speed intervene on the MCP to a speed other than that on the VNAV DES page then your VNAV profile deviation pointer will be wrong because it will still be based on the speed in the VNAV DES page.

However, if you overtype the speed on the VNAV DES page then the FMC will recalculate the profile and your pointer will be accurate.


Simon Kelsey

sig_FSLBetaTester.jpg

 

Share this post


Link to post
Share on other sites

Thanks all. Seems there isn't as much to it as I thought.


Prepar3Dv5 | ASUS Maximus XI Code Z390 | i9 9900K 5 GHz | Corsair Vengeance RGB Pro 32 GB DDR4 3600 MHz | GeForce RTX 2080 Ti 11 GB GDDR6 MSI Lightning Z Windows 10 Pro 64 bit | Samsung 850 EVO 1 TB | Samsung 43'' 4K curved TV | HP Reverb 2 VR HMD | Agronn 737 Captain's Yoke | FSC 737 Throttle Quadrant | Saitek Pro Flight Rudder Pedals

 

Share this post


Link to post
Share on other sites
8 hours ago, Canuck said:

I always used the speeds that were calculated by the FMC with the information I put in because I took the 'don't mess with it, it's more intelligent than me' approach and thought I would mess the descent profile up when changing speeds manually.

In N. America, you'd be a speedbump if you're descending at 250 out of FL260. Many of the airports I fly to have a 280 knot target for the first speed and it's reduced as the STAR progresses. I'm heading to ORD in a bit and I wouldn't be surprised if they assign me 300 for the descent.


Matt Cee

Share this post


Link to post
Share on other sites

I was gonna say 250 from the Flight Levels wont get you down fast enough as required. I often have trouble complying with the altitude constraints when using 280 and more like 300 is necessary with even a slight tailwind.


Alberto Ferracuti

Share this post


Link to post
Share on other sites
5 hours ago, Spin737 said:

I'm heading to ORD in a bit and I wouldn't be surprised if they assign me 300 for the descent.

That's pretty much guaranteed if they are landing to the West.


Joe Diamond

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

  • Tom Allensworth,
    Founder of AVSIM Online


  • Flight Simulation's Premier Resource!

    AVSIM is a free service to the flight simulation community. AVSIM is staffed completely by volunteers and all funds donated to AVSIM go directly back to supporting the community. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. Thank you for your support!

    Click here for more information and to see all donations year to date.
  • Donation Goals

    AVSIM's 2020 Fundraising Goal

    Donate to our annual general fundraising goal. This donation keeps our doors open and providing you service 24 x 7 x 365. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. We reset this goal every new year for the following year's goal.


    17%
    $4,420.00 of $25,000.00 Donate Now
×
×
  • Create New...