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CI and STAR speed restrictions

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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?

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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.

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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.

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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.

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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. 

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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.

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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.

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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

 

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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.  

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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.

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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.

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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.

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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.

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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.

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8 hours ago, JoeDiamond said:

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

Chop and drop over MDW STARs and DTW/CLE streams? It's been a while since I've paid any attention to C90 procedures (and even then, I was really only looking at the Best-Equipped, Best-Served concept, which would've been applied only in select situations to mitigate ORD/MDW interaction).

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16 hours ago, Spin737 said:

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.

Just flew into KOMA at .78/280/250 and was down in no time. I fly into KORD a lot and I'm relieved it's only the virtual KORD. I would have suffered a verbal slap via comms I'm sure...

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42 minutes ago, Canuck said:

Just flew into KOMA at .78/280/250 and was down in no time. I fly into KORD a lot and I'm relieved it's only the virtual KORD. I would have suffered a verbal slap via comms I'm sure...

RW I've done .84/320 with 320 all the way down to ten going into KORD.

blaustern

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