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FMS Hard Speed Restrictions

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    FMS Hard Speed Restrictions

    Hi, Community;

    Please be informed that we are making on FMS loading , in legs page, any fix doesnt shows its' speed correctly on any SID or any STAR point fix which has includes with a maximum speed of constraint, on the otherhand, speed is always shows as named ''Hard'' type putted-up originated from the system or caused by AIRAC or it may not be a reason which is not originated from PMDG Product, actually I dont know, but if there is a MAX speed on any procedure it must not be ''Hard'' type putted-up on legs page.

    For instance; charts shows MAX230ktsbut the FMS data shows typically as 230kts(230/------) ,so its must not be only ''230'' value as a hard type setted , it must be looking such as 230B/------ like that....( this means is MAX 230 so 230 or Below) , any chance to fix it with a new update..


    Screenshots:

    SID Chart
    https://ibb.co/1nZvR7Q

    Incorrect
    https://ibb.co/xCTJMFq

    Correct
    https://ibb.co/gZf50GD


    Best Regards
    Erkal SANLI
    Erkal SANLI - LTFJ

    #2
    That's not PMDGs fault. PMDG airplanes (and all other airplanes in the simulator) use external NAVDATA. What you see on the legs page is only as good as that external NAVDATA. It's not a bad thing. Pilots always have to reference the chart to find any differences and, although it's not frequent, we sometimes have to correct a few things here and there based on some previous experience with certain ATC or actual differences with the charts. Some companies have different providers for FMC navdata and for charts. For instance, they may use LIDO for charts and JEPPESEN for NAVDATA. All of them comply with the AIP, but there will be differences in speeds and altitudes. The most common difference I find is a hard altitude on the IF just before the FAF/FAP. Some charts aren't planned for continuous descent approaches, so we always clean it up and change it to "or above" to make a continuous approach. If you see a 230/ and you think it should be 230B/, just change it.
    Last edited by Aeromar; 22May2020, 23:45.
    Omar Josef, from Spain
    737/757/767 Rated
    Still use the damn simulator

    Comment


      #3
      My knowledge of VNAV/LNAV navigation is very basic (if talking about real life) and this applies also on the 737. But I think that the "at or below"/"at or above", that in the CDU is marked as xxxxB/xxxxA, can be applied only for altitudes.

      Speed is automatically decided by the FMC using the CI, and the number you see on the CDU (230 in this case) is just the limit. So the airplane know it can fly at whatever speed based on the CI, but it must not exceed that limit. That's the reason why in the final fixes of an approach, the speed on the CDU is almost always the maximum allowed speed for that approach, but of course, you'll never fly at that speed, but use a speed intervention.
      In other words, it should be correct like that, as many times I had the NGXu flying at a lower/higher speed than the one written in the CDU but it was within the range.

      I might be terribly wrong because I don't know how the real one works, but it's my impression that it should be correct.

      Edit: turned out I was wrong (as always) and it's not an issue of the aircraft, but of the NAVDATA
      Giovanni D. Tarar
      FAA CPL+IR Single & Multiengine Land
      I love flying when I'm in a bad mood

      Comment


        #4
        I see you've edited, but yeah, you can also set a "or below" for speeds in the FMC. CI only affects speeds when you're in ECON but legs, SLP and speed transition restrictions have priority over ECON speed.

        A speed is a limit when it has "or below". For example, if the airplane wants to be at the IF at 180kts (small letters) to comply with FAF/FAP speed, if you type in 220B (big letters) it will still be fly that point at around 180kts. Of course the winds entered in the forcast page have to be accurate for that speed to match what'll actually happen, as 180 is just a passing speed to meet the next hard restriction. Now, if you type in 250/ at the IF, it will fly 250kts but it'll start complaining shortly after. You may get "DES PATH UNACHIEVABLE" "DRAG REQUIRED" or, depending on which FCC version, it might even kick you out of VNAV PTH altogether and revert to VNAV SPD.
        Omar Josef, from Spain
        737/757/767 Rated
        Still use the damn simulator

        Comment


          #5
          I look at the FMC differently than most since I'm old. The FMC is just a reference, it is the pilot's responsibility to make sure the airplane conforms to the various restrictions imposed by the navigational charts and ATC instructions. The way I was trained was all speed and altitude restrictions were hard loaded into the MCP. This was assurances that no altitudes or speeds were busted. When below 100 (that's ten thousand feet) the MCP was changed to FLCH. This may seem like a lot of work, but if busting a clearance or landing short is career limiting, it's is no problem at all.

          I know I'm old and I still miss the seven-oh-seven.
          Bode Bridges
          I Earned my Spurs in Vietnam

          Comment


            #6
            Dear CBT_Phoenix,

            First of all, I would like to say to thanks for you for your detailed contribution...,

            As we know; Cost Index (CI) is nothing new - most Flight Management System have been using it in some format for years.

            The lower the CI, the more "importance" the machinery places on saving fuel. Low cost indexes will result in lower climb speed, (both indicated and mach), lower cruise speed, a generally higher cruise altitude, a later descent and a slower descent mach/speed. The higher CI's will result in the opposite.

            A given cost index will result in a specific still air True Airspeed at altitude - however, it is normal for the FMS to adjust the mach number (MN) by .01 when the head wind or tail wind components exceed a programmed threshold value - ie, the airplane will slow down with a tail wind, speed up with a headwind (automatically) by .01 mach in an effort to minimize the fuel burn. More sophisticated/Integrated flight planning programs or similar apps will show this change on a leg by leg basis and will file the speed change as part of the ATC flight plan.

            But I am talkin about Constraints speed which is designated on a chart at somewhere to must correct it if its wrong...


            Best Regards
            Erkal
            Erkal SANLI - LTFJ

            Comment


              #7
              Again. That's not PMDGs part of the job. That is something related to the NAVDATA provider, in this case NAVIGRAPH. Most of us have a subscription at https://www.navigraph.com/ to get monthly AIRAC packages for the sim. PMDG still doesn't make full use of the system, as it doesn't support the newer types of ARINC segments, such as radius to fix and all that, but manages to get a decent path by setting points to define arcs. The amount of discrepancies I have found in Navigraph updates is not that much higher than what I find in the real airplane. It's very impressive.
              Omar Josef, from Spain
              737/757/767 Rated
              Still use the damn simulator

              Comment


                #8
                Originally posted by Bluestar View Post
                I look at the FMC differently than most since I'm old. The FMC is just a reference, it is the pilot's responsibility to make sure the airplane conforms to the various restrictions imposed by the navigational charts and ATC instructions. The way I was trained was all speed and altitude restrictions were hard loaded into the MCP. This was assurances that no altitudes or speeds were busted. When below 100 (that's ten thousand feet) the MCP was changed to FLCH. This may seem like a lot of work, but if busting a clearance or landing short is career limiting, it's is no problem at all.

                I know I'm old and I still miss the seven-oh-seven.
                Yeah, that's old school. There are some places where we can still fly like that, but nowadays the SOP culture in most companies pushes us to use as much of the airplane as possible. Although you could just hand fly a glide to the airport, the current reality of airspace and noise restrictions require a lot more precision. You'd think setting up a precise VNAV is less work but that's not accurate. Although we prepare our descents before we even start descending, it's not completely hands off and we're still doing the old "levels x3" in our heads all the time as we monitor VNAV making sure the airplane starts decelerating when it should. There's nothing more satisfying than reaching the wanted speed without having used speedbrakes or flaps and not having the thrust levers stand up as you extend flaps. My old company was far more oldschool than the company I'm at right now. It's less safe because you're only relying on having understood the clearance correctly. If you have a VNAV constraint that doesn't agree with the clearance you've received, at least that'll trigger a request to confirm cleared level.
                I remember in my old company, whenever ATC started moving us around, most of us would just revert to simpler modes, such as LVL CHG or even V/S to feel more in control. I've understood now that the reason for that is an incomplete understanding of how VNAV works and its great superiority over LVL CHG (Even VNAV SPD). In my current company, I've been trained in a way that, as soon as ATC starts giving us levels and speeds, we immediately reconfigure VNAV in matter of seconds, to have a better guarantee of meeting speed and altitude restrictions. And then we go back to the old "levels x3 + tens of speed".
                Last edited by Aeromar; 23May2020, 15:50.
                Omar Josef, from Spain
                737/757/767 Rated
                Still use the damn simulator

                Comment


                  #9
                  Dear Omar,

                  Thanks for your reply and contribution.

                  Best Regards
                  Erkal SANLI - LTFJ

                  Comment


                    #10
                    Yes unfortunately I noticed straight away my mistake. But as Omar said, usually there's a cross-check with the charts, and if something mismatch, the pilots can make an intervention (either on the MCP or in the FMS).
                    I wonder if NavData and Charts providers (for simulators) are aware of this, and if they are, why they are not correcting it...
                    Giovanni D. Tarar
                    FAA CPL+IR Single & Multiengine Land
                    I love flying when I'm in a bad mood

                    Comment


                      #11
                      Originally posted by CBT_Phoenix View Post
                      Yes unfortunately I noticed straight away my mistake. But as Omar said, usually there's a cross-check with the charts, and if something mismatch, the pilots can make an intervention (either on the MCP or in the FMS).
                      I wonder if NavData and Charts providers (for simulators) are aware of this, and if they are, why they are not correcting it...
                      They use the same AIRAC used by the real life NAVDATA. They just put together the FMC navigation database with a little less love. You have to keep in mind that these updates that we use in the sim are generic and valid for all types. In real life, the validation and certification layers are much much more strict and every update is tailored for a specific type and a specific company. Sometimes what you see in a Navigraph update is exactly what was published in the national AIP, so basically it's legal and it complies. Most of the times 230/ is as legal as 230B and, sometimes /3000 is as legal as /3000A. So if the AIP has a minimum altitude expressed as a hard altitude for the IF, maybe a certain company's requirements to fly continuous descent approaches has his provider change it to "or above", as long as it also complies with the AIP. So if you're using LIDO, Jeppessen or Navtech charts, the only way to find exactly the same altitudes and speeds in the FMC is by also getting FMC updates from the provider of your charts. This is the difference between having a million € tailored service from Jeppesen in real life and having a cheap subscription to Navigraph. Navigraph is good enough. Of course having a real company provided EFB with real charts (and performance) is a plus.
                      Last edited by Aeromar; 23May2020, 19:30.
                      Omar Josef, from Spain
                      737/757/767 Rated
                      Still use the damn simulator

                      Comment


                        #12
                        Originally posted by Aeromar View Post

                        They use the same AIRAC used by the real life NAVDATA. They just put together the FMC navigation database with a little less love. You have to keep in mind that these updates that we use in the sim are generic and valid for all types. In real life, the validation and certification layers are much much more strict and every update is tailored for a specific type and a specific company. Sometimes what you see in a Navigraph update is exactly what was published in the national AIP, so basically it's legal and it complies. Most of the times 230/ is as legal as 230B and, sometimes /3000 is as legal as /3000A. So if the AIP has a minimum altitude expressed as a hard altitude for the IF, maybe a certain company's requirements to fly continuous descent approaches has his provider change it to "or above", as long as it also complies with the AIP. So if you're using LIDO, Jeppessen or Navtech charts, the only way to find exactly the same altitudes and speeds in the FMC is by also getting FMC updates from the provider of your charts. This is the difference between having a million € tailored service from Jeppesen in real life and having a cheap subscription to Navigraph. Navigraph is good enough. Of course having a real company provided EFB with real charts (and performance) is a plus.
                        Or we can ask Jeppesen for a custom made NavData 😁
                        Anyway, what you said brought up an important difference between sims and RL. On the simulator there is no regulating entity, and no strict boundaries for those who offer these services.
                        There's obviously a serious difference between a multi-million airplane flying hundreds of people, and a software flying on another software.

                        But to be honest, since those "issues" in the end, are not incorrect NavData, I don't find it so bothering; as if you're flying offline, there's no one enforcing those restrictions, while if flying online with ATC, most of the time the Approach will give speed restrictions based on the current amount of traffic. Anyway there might be some people that aim at the absolute realism (and I understand them), and may find the lacking of the B before 230 an issue to be corrected. I'm tempted to ask whether Navigraph or NavData Pro will ever make custom NavData for each airplane (or at least the most used ones), but I know almost for sure that this is not going to happen very soon, and it will cause an increase in the subscription price.

                        Thank you for the explanation of how these things work in real life. Something new to add on the personal knowledge database 😊
                        Giovanni D. Tarar
                        FAA CPL+IR Single & Multiengine Land
                        I love flying when I'm in a bad mood

                        Comment


                          #13
                          Hi,

                          if it originated from the AIRAC datas, the same problem should be experienced on all the different planes, no problems at charted altitudes, there was only speed that I mean


                          Best Regards
                          Erkal SANLI

                          Erkal SANLI - LTFJ

                          Comment


                            #14
                            Originally posted by Aeromar View Post

                            Yeah, that's old school. There are some places where we can still fly like that, but nowadays the SOP culture in most companies pushes us to use as much of the airplane as possible. Although you could just hand fly a glide to the airport, the current reality of airspace and noise restrictions require a lot more precision. You'd think setting up a precise VNAV is less work but that's not accurate. Although we prepare our descents before we even start descending, it's not completely hands off and we're still doing the old "levels x3" in our heads all the time as we monitor VNAV making sure the airplane starts decelerating when it should. There's nothing more satisfying than reaching the wanted speed without having used speedbrakes or flaps and not having the thrust levers stand up as you extend flaps. My old company was far more oldschool than the company I'm at right now. It's less safe because you're only relying on having understood the clearance correctly. If you have a VNAV constraint that doesn't agree with the clearance you've received, at least that'll trigger a request to confirm cleared level.
                            I remember in my old company, whenever ATC started moving us around, most of us would just revert to simpler modes, such as LVL CHG or even V/S to feel more in control. I've understood now that the reason for that is an incomplete understanding of how VNAV works and its great superiority over LVL CHG (Even VNAV SPD). In my current company, I've been trained in a way that, as soon as ATC starts giving us levels and speeds, we immediately reconfigure VNAV in matter of seconds, to have a better guarantee of meeting speed and altitude restrictions. And then we go back to the old "levels x3 + tens of speed".
                            Omar,

                            The new technology is nice, but when the magenta line and the automation goes away some folks are going to struggle.

                            I can remember coming into PANC at three in the morning in the middle of December on day 12 of a ten day trip and having to shoot the ILS 07R (the numbers have changed) and circling to RWY33 with the weather a minimums and base was downwind (tired, night, and bad weather a recipe for disaster). This approach was flown by hand and no autothrottle. The RNAV RWY33 and the new magic would have make life easier and a lot safer.

                            We also had an advantage with the third man in the cockpit, the F/E. He made life so much easier especially when there was an issue with the airplane (which was extremely rare.)


                            Bode Bridges
                            I Earned my Spurs in Vietnam

                            Comment


                            • Michael Codd
                              Michael Codd commented
                              Editing a comment
                              I bet your poor F/E was made to do the external check in the freezing cold before you left PANC ? So cheer up Bode, because you didn't have to eat the crew chicken and I'm sure there are a lot of young at heart guys out there who still remember sitting in the hot cockpit of the seven-oh-seven with the same sort of passion you have for it, in spite of the fact that it never had an FMS and only a few had INS fitted (not including the KC135).

                            • Bluestar
                              Bluestar commented
                              Editing a comment
                              Michael we had professional F/Es and most of them had been with the company before I was born. When I had time I would do a walk around with them. They forgot more about airplanes than I would ever know. As for navigation all the aircraft flying the NOPAC routes had dual Civa INS which was very good. I was setting on the ground at KSUU and checked the distance to PHNL and they were within 0.1 miles of each other. It is my opinion that the real Civa INS units were much better than what I've seen simulated.
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