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Glide slope diamond never showed up on Approach

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    Glide slope diamond never showed up on Approach

    I flew the following flight plan below, and when on final approach to RWY28R, after capturing the LOC with the APP armed in the 747-8, the G/S Diamond never appeared in the PFD. I was forced to abort the approach as the weather/smoke at KSFO was really bad. I made a similar flight a few days earlier from KDEN to KSFO, landing on RWY 28R again, and experienced the same issue.

    KDEN 35L.COORZ6.VOAXA OAL.MOD9 DUMBA ILS RWY 28R KSFO

    To see if I could reproduce the same issue quickly. I flew a local circuit at KSFO, taking off from RW28R and landing on RW28R. The Glide Slope worked perfectly two times in a row!

    Any idea on what would cause this, or if I set something incorrectly?

    Bill Clark
    Bill Clark
    Win10, V-2004//I5-8600K 5.2GHz//Nvidia GTX 1080Ti//VRAM 11GB
    RAM 32GB//2TB M2.NVMe//Gigabyte Z370 Gaming 7//Corsair H115i

    #2
    Do not arm APPR until after you see the GS deviation indicator. Before it appears only arm the LOC/VOR.

    You didn't mention any altitudes flown so one cannot dissect the exact problem. Note crossing CEPIN 3000A the GS is actually above 3200 ft at that point and I'll typically hold the 3000 until the GS decreases to that altitude and then commence the descent, or I'll use V/S to set a gentle 500 ft/min descent to GS intercept.
    Dan Downs KCRP
    i7-10700K 32GB 3600MHz 1080Ti

    Comment


      #3
      Thanks Dan,

      In the past, I have always engaged APP button shortly after the LOC turns green............been doing that for many years in PMDG A/C with no issues.

      Is the G/S deviation indicator the tiny little diamond in black outline that appears on right side of PFD?

      As I recall I did see that when G/S failed.

      Bill Clark
      Bill Clark
      Win10, V-2004//I5-8600K 5.2GHz//Nvidia GTX 1080Ti//VRAM 11GB
      RAM 32GB//2TB M2.NVMe//Gigabyte Z370 Gaming 7//Corsair H115i

      Comment


        #4
        Originally posted by Bingo041 View Post
        Thanks Dan,

        In the past, I have always engaged APP button shortly after the LOC turns green............been doing that for many years in PMDG A/C with no issues.

        Is the G/S deviation indicator the tiny little diamond in black outline that appears on right side of PFD?

        As I recall I did see that when G/S failed.

        Bill Clark
        That works fine unless the aircraft is equipped with IAN. The GS deviation indicator is the diamond on right vertical axis, yes.
        An IAN equipped aircraft, such as the 747-8, will not capture GS if APPR is armed before it is live because it automatically sets up an IAN approach (G/P instead of G/S) and ignores G/S.
        Dan Downs KCRP
        i7-10700K 32GB 3600MHz 1080Ti

        Comment


          #5
          Thanks again Dan,

          Is this diamond the same size and color as the captured G/S?

          I need to know what to look for?

          Bill Clark
          Bill Clark
          Win10, V-2004//I5-8600K 5.2GHz//Nvidia GTX 1080Ti//VRAM 11GB
          RAM 32GB//2TB M2.NVMe//Gigabyte Z370 Gaming 7//Corsair H115i

          Comment


            #6
            The diamonds (for both LOC and GS) turn green once captured, when the diamond first appears then you are receiving the signals and you can arm the approach modes. I believe it is white until captured... or maybe just an outline. I haven't been in the -8 for a couple of weeks.
            Dan Downs KCRP
            i7-10700K 32GB 3600MHz 1080Ti

            Comment


              #7
              Ok, I will experiment later today if I can get to it, to see what I can figure out.

              Thanks,
              Bill Clark
              Bill Clark
              Win10, V-2004//I5-8600K 5.2GHz//Nvidia GTX 1080Ti//VRAM 11GB
              RAM 32GB//2TB M2.NVMe//Gigabyte Z370 Gaming 7//Corsair H115i

              Comment


                #8
                [QUOTE=DDowns;n83824]The diamonds (for both LOC and GS) turn green once captured, when the diamond first appears then you are receiving the signals and you can arm the approach modes. I believe it is white until captured... or maybe just an outline. I haven't been in the -8 for a couple of weeks.[/QUOTE

                I see some wrong statements here.

                400 and -8 has does not have LOC/VOR switch, it's only LOC.

                On the -8 performing an IAN or any approach you can arm the APP mode anytime, there is no such thing as not to arm APP (not APPR) unless you see GP (not GS indication).

                There are recommended procedures at different airlines as to how to do the transition from one to the other.

                Usually, you are on vectors to intercept and when you cleared for the approach you will arm APP mode, verify LOC/FAC, and GP armed.

                Now, if you still in LNAV to intercept the final course you need to pay attention that LNAV might parallel the localizer without actually capture it, so if that's the case you need to use HDG SEL or HDG HOLD to intercept.

                Something else worthy of mentioning here,
                If the APP switch is pushed and the selected approach does not have a glidepath , the advisory FMC MESSAGE displays, and the FMC APP UNAVAIL – GP message appears in the CDU scratchpad.

                The diamonds (for both LOC and GS) turn green once captured



                Those "diamonds" actually localizer/glideslope pointers they are not green by any means, actually, magenta and they fill in a solid color when within 2 1/3 dots of the center scale.
                I guess you are a bit confused with some other airplane.
                My question is why it did not capture the GS, what actually happened.

                Last edited by Aurel Vlaicu; 16Sep2020, 01:37.
                Aurel Vlaicu

                Comment


                  #9
                  Bill,
                  Out of curiosity, I did a couple of flights between KOAK and KSFO to ILS28R and a few KSFO DEP/ARR to ILS28R and did not have any issues.
                  I'm very careful here not to say that it didn't happen, would be possible to remember what it did actually happened in your case?
                  Do you remember the FMAs and if you had any messages? I didn't notice any malfunction that we can induce as a G/S failure to say that it was active?
                  It could be an intermittent software bug or a P3D issue, very difficult to determine with so little info.
                  Aurel Vlaicu

                  Comment


                    #10
                    Bill,

                    it’s just a guess because Inhave experienced something more or less similar, would you please check if your P3D map says ILS or something else if you click ON the green beam?

                    Background is, I had installed FSAerodata and it was placed in my library automatically. It caused SOME ILS to disappear like Salt Lake City, others became LOC only. In my case I could resolve it by placing the FSAD entries at the bottom of my library.

                    Even if you don‘t use FSAD it‘s absolutely unlikely that the diamonds just don‘t appear for no special reason when they do for others but I would expect something like this to happen if the scenery, some bgl, etc gets corrupted. Ever noticed it somewhere else?
                    i7-6700k, GTX 1080TI, 32GB DDR4 RAM @2666MHz, 4k
                    Marc Ehnle

                    Comment


                      #11
                      Dan, and others,

                      I am in the process of flying another flight into KSFO. Attached is a screenshot of my PFD and ND showing LOC active, and the tiny diamond you said is where the G/S is receiving signals? Once this appears symbol the press the APP to arm the G/S?

                      Bill Clark
                      ND & PFD Pre-glidelope.jpgND & PFD Pre-glidelope.jpg

                      Bill Clark
                      Win10, V-2004//I5-8600K 5.2GHz//Nvidia GTX 1080Ti//VRAM 11GB
                      RAM 32GB//2TB M2.NVMe//Gigabyte Z370 Gaming 7//Corsair H115i

                      Comment


                        #12
                        The diamond is just above the VNAV descent deviation indicator is a G/P indicator because you are in IAN mode. Note FAC is indicated on the FMA. This means you are in IAN mode and will not be able to capture the GS; rather, it will attempt to capture a GP (glide path). LOC is not active, were it then FMA would indicate LOC and not FAC (final approach course is an IAN mode indication). The on course indication is not an indication that you are on the LOC rather you are on a path defined by the FAF.

                        It is unknown from the information you have provided how you initiated the IAN mode rather than ILS coupled approach. What led up to this point? When did you change from LNAV to FAC?
                        Last edited by DDowns; 16Sep2020, 21:16.
                        Dan Downs KCRP
                        i7-10700K 32GB 3600MHz 1080Ti

                        Comment


                          #13
                          Dan,

                          I didn't do anything to change to IAN mode, in fact, I don't even know what IAN mode is. I just entered RWY 28R (ILS), and expected to get a LOC and G/S. Attached is a shot of the entire panel in full size, so by slide the bars possibly you can see what I may have done inadvertently, or I have a problem with my system? G/S failed.

                          Any ideas, I see you can open image in new tab to enlarge it?

                          Bill Clark

                          Glideslope Failuer.jpg
                          Last edited by Bingo041; 16Sep2020, 22:32.
                          Bill Clark
                          Win10, V-2004//I5-8600K 5.2GHz//Nvidia GTX 1080Ti//VRAM 11GB
                          RAM 32GB//2TB M2.NVMe//Gigabyte Z370 Gaming 7//Corsair H115i

                          Comment


                            #14
                            Originally posted by Bingo041 View Post
                            Dan,

                            I didn't do anything to change to IAN mode, in fact, I don't even know what IAN mode is. I just entered RWY 28R (ILS), and expected to get a LOC and G/S. Attached is a shot of the entire panel in full size, so by slide the bars possibly you can see what I may have done inadvertently, or I have a problem with my system?

                            Any ideas?

                            Bill Clark
                            Bill... I've been trying to explain something to you that apparently is totally foreign and unknown. The 744 doesn't have IAN, the 748 does.

                            Please see the FCOM NP.21.42 Landing Procedure ILS/GLS: Verify the LOC and G/S pointers are shown BEFORE (emphasis mine) Arm the APP mode.

                            As I suggested in my first post in this thread.... if you arm APPR before those pointers (diamonds) are showing then you enter IAN mode.

                            IAN mode procedure FCOM NP.21.44.

                            Try also Google Boeing IAN for additional information. It's time to become familiar with the features of the -8 my friend.
                            Dan Downs KCRP
                            i7-10700K 32GB 3600MHz 1080Ti

                            Comment


                              #15
                              Bill,

                              Depending on how you flew the arrival it could be that it‘s a P3D inaccuracy that catches you. Dan explained it already, your 747 is in IAN mode, it‘s Integrated Approach Navigation, where the airplane (748 and 737NG) follow a theoretically simulated ILS profile to the runway. It‘s based on the airplane-own nav systems GPS and IRS. It calculates a 3 degree glide slope to the runway and to make it clear that the plane is not on the ILS it names it FAC and GP on the FMA, glide PATH.

                              This mode can be used if no ILS is available but the pilots want to fly an ILS-like approach, for example if the aurport does not have any instrument approaches available. But other than ILS IAN does not feature an autoland capability. I believe it‘s handled with the rules comparable to an RNAV approach.

                              The thing with P3D is that sometimes, all above when you enter the final approach from a straight-in arrival, the magenta line is drawn slightly next to the extended centerline. So if you come in with LNAV and VNAV, the airplane sometimes doesn‘t recognize that there is a localizer to capture and turns on IAN (FAC). If it does that it is not able to switch to LOC by itself anymore. So it waits for that simulated 3 degree glideslope and captures it, but not using its ILS receivers but using GPS/IRS and the database and it announces GP.

                              So what you can do: use HDG SEL to fly an intercept heading with the centerline and when you are on this intercept heading you can arm APPR mode. The plane will correctly recognize the ILS and will capture the localizer, announced as LOC in the middle.
                              i7-6700k, GTX 1080TI, 32GB DDR4 RAM @2666MHz, 4k
                              Marc Ehnle

                              Comment


                                #16
                                Marc, thanks very much for your explanation of ILS IAN. You explained its potential use pretty clearly.

                                I followed up by reading FCOM pages NP.21.42 thru NP.21.45 where the procedures of a traditional ILS versus this "GPS" IAN approach is covered. My main takeaway is to use APP button, and not LOC, but be aware of the risk using LNAV, as HDG SEL may be a safer mode.

                                My next question is, when do you use LOC button, I would think for localizer only approaches?

                                I had a successful flight a few minutes ago and the LOC and G/S were active as expected.

                                Thanks again,
                                Bill Clark
                                Bill Clark
                                Win10, V-2004//I5-8600K 5.2GHz//Nvidia GTX 1080Ti//VRAM 11GB
                                RAM 32GB//2TB M2.NVMe//Gigabyte Z370 Gaming 7//Corsair H115i

                                Comment


                                  #17
                                  Bill, as you might have found out already, the best way to guarantee you will always capture a valid ILS signal safely in the B744/-8 is to avoid using LNAV/VNAV modes and use HDG and ALT modes instead. The protection range for the use of an ILS is approx 30nms maximum from the transmitter. However, provided the aircraft's PFD is displaying the correct ILS information then the ILS LOC and G/S signals can be relied on and there is no need to check the ILS ident before it can be used in anger. Bear in mind that the FMA annunciations are key to everything you do with the AP and FD selections, so you need to familiarise yourself with them and know what you expect to see during a manual or automatic ILS approach. Always include them in your Instrument scan throughout the approach.

                                  You should select FLCH (or V/S - with care) for the intermediate descent down to the initial approach altitude. If you plan things correctly then ideally you will slow down and extend Flaps on schedule as you get closer so that you maintain a low thrust continuous descent until capturing the ILS glideslope. As soon as you are on an intercept heading to the ILS LOC centreline (e.g. on a 30 to 45 deg intercept angle) you should arm the LOC mode - there is no need to wait for it to become active and DO NOT arm APP mode yet. Always plan to capture the LOC below and before the glideslope, so that the aircraft is stable at the initial approach altitude and on the LOC centreline before the glideslope becomes active. As soon as the autopilot has captured the LOC and it is tracking inbound nicely then that is the time to arm APP mode. The AP/FD will eventually capture the G/S and the aircraft will start to descend on the ILS. At this stage the LOC and G/S annunciations you see on your PFD will both be green. I hope this simple explanation is helpful.
                                  Michael Codd

                                  Comment


                                    #18
                                    Thanks Michael for your detailed response,

                                    Dan, one of our forum monitors, recommended that I refer to the following, which I did:

                                    "Please see the FCOM NP.21.42 Landing Procedure ILS/GLS: Verify the LOC and G/S pointers are shown BEFORE (emphasis mine) Arm the APP mode."

                                    There is no mention of Arming of the LOC button in the Boeing manual, on the pages prior to, or pages after that which is mentioned above. What you are recommending is what I used to do all the time. Apparently, all that is needed NOW, is to just "verify the LOC/FAC and GP pointer are shown in the correct position. Then Arm APP mode." If this is what professional pilots do, then when is the LOC button used?

                                    So what you stated works well for you, but it seems like the way Boeing implemented another new feature not available to older 747's, is a GPS mode capability at runways with no ILS. Because of this new feature, the ILS procedure of the 747-8 was designed to deviate slightly from the 747-400?

                                    I'm not an an airline pilot, so I depend on forums like this one, PMDG documentation (well done), and YouTube videos to help me. The Boeing manual provides official information, but a good training program at major airlines, I assume, have instructors that provide context lacking in official aircraft manufacturers manuals.

                                    Bill Clark
                                    Bill Clark
                                    Win10, V-2004//I5-8600K 5.2GHz//Nvidia GTX 1080Ti//VRAM 11GB
                                    RAM 32GB//2TB M2.NVMe//Gigabyte Z370 Gaming 7//Corsair H115i

                                    Comment


                                      #19
                                      The Boeing manuals supplied with your PMDG aircraft are approved 'generic' documents and you should follow those procedures if you are happy with them. Different airlines will adopt their own approved standard operating procedures and these will often differ from Boeing's procedures to a greater or lesser extent. So for example, it is permissible to use LNAV and VNAV for the initial approach provided the complete arrival procedure is programmed into the FMS, but when any last minute ATC changes or constraints are given it is more appropriate to manage the flight using the MCP heading selector and altitude windows. You can arm LOC anytime you are on an ILS intercept and whilst keeping an eye out for the ILS indicators once you are established inbound then arm the APP mode. Time permitting the legs sequencing page in the FMS CDU's would also be tidied up by the non-handling pilot.

                                      The maximum intercept angle for the localiser is 120 degrees, but G/S capture will not occur if the intercept angle to the localiser is greater than 80 degrees. Initially arming LOC instead of APP is a standard operating procedure adopted by several B744 operators I know of. It reduces the risk of capturing a false glideslope lobe before the aircraft is fully established on the ILS Localiser centreline. Incidentally, this is one of the reasons why you are quite right about not arming APP before the ILS raw data indicators are both active. Establishing on the localiser using LOC before arming APP mode also avoids any risk of the aircraft descending on the glideslope below the Initial or Final Approach altitude when it is not yet fully established inbound on the ILS centreline - to descend like this is a definite NO, NO in any pilot's instrument flying handbook!

                                      The trap you seem to have fallen into on your approach - at least as far as the aircraft's failure to descend after AXMUL is concerned - is that although you had programmed the correct ILS for 28R into the FMS you still had VNAV active (others have already explained about the differences between ILS and IAN approaches). Your aircraft had just passed over AXMUL and the FMA indication confirmed that it had only just captured the 1,800ft as set in the MCP altitude window (hence the momentary green box around the VNAV ALT annunciation). Unfortunately, as you no doubt discovered, the aircraft will stay sitting at 1,800ft ad infinitum with VNAV ALT mode active and 1,800 ft set in the MCP altitude window until you do something about it; or until the aircraft runs out of fuel and then it will definitely start to descend!
                                      Last edited by Michael Codd; 18Sep2020, 22:45.
                                      Michael Codd

                                      Comment


                                        #20
                                        Michael,

                                        Thanks very much, you offer good advice.

                                        A lot of information has been presented in this thread, and it is much appreciated. I would prefer using the LOC button. I have been flying PMDG A/C for many years so I'm pretty good at managing speeds, headings, and altitudes. I just was not aware of this IAN feature that caught me off guard.

                                        I have several airline pilot friends, unfortunately, none of them have ever flown this newer version of the 747.

                                        Bill Clark
                                        Bill Clark
                                        Win10, V-2004//I5-8600K 5.2GHz//Nvidia GTX 1080Ti//VRAM 11GB
                                        RAM 32GB//2TB M2.NVMe//Gigabyte Z370 Gaming 7//Corsair H115i

                                        Comment


                                          #21
                                          Michael,

                                          the only thing about that - on a second glance - is, why does Bill‘s aircraft arm GS mode while it has captured FAC and remains in VNAV? I have overseen that the first time I watched his screenshot. It was my understanding that as soon as the plane enters IAN it won‘t show an ILS mode anymore. But it seems that while it‘s in IAN laterally it still waits for the vertical ILS mode. Is that correct or could there be a little bug?
                                          i7-6700k, GTX 1080TI, 32GB DDR4 RAM @2666MHz, 4k
                                          Marc Ehnle

                                          Comment


                                            #22
                                            Originally posted by Ephedrin View Post
                                            Michael,

                                            the only thing about that - on a second glance - is, why does Bill‘s aircraft arm GS mode while it has captured FAC and remains in VNAV? I have overseen that the first time I watched his screenshot. It was my understanding that as soon as the plane enters IAN it won‘t show an ILS mode anymore. But it seems that while it‘s in IAN laterally it still waits for the vertical ILS mode. Is that correct or could there be a little bug?
                                            The problem I have is not knowing exactly what Bill was doing to the FMS legs, autopilot modes and FMA indications before AXMUL, so I can't honestly give you a definite answer. However, I do not believe there is a bug, because if you look closely at Bill's first image there isn't a G/S armed annunciation and the AP/FD is in a VNAV PTH descent, which is what I would expect to see during an IAN procedure. In his second image there is a G/S armed indication but the aircraft is already high for an ILS approach at this point, having levelled off at 1,800 ft. It has already flown through the G/S just before reaching this position, so it is obviously now above and beyond the capture range for the G/S signal. Furthermore, the FMS was never programmed correctly for an IAN approach, because if you look at the IAN procedures for RWY 28R at KSFO and compare them with the ILS plate you will see the position AXMUL appears on the ILS plate. No wonder the autopilot was confused!!! 😂 🤓
                                            Last edited by Michael Codd; 19Sep2020, 10:35.
                                            Michael Codd

                                            Comment


                                            • Ephedrin
                                              Ephedrin commented
                                              Editing a comment
                                              ah, yes I haven't gone into the charts, thanks

                                            #23
                                            I thought I would show you what I did originally as I attempted to duplicate the flight that started this thread.

                                            Normally this STAR and ILS RW28R starts with a VECTOR prior to DUMBA (1st image).

                                            I overwrote the VECTOR with DUMBA to complete a direct LNAV and VNAV path to the runway (2nd image).

                                            I waited later in the path this time to press the LOC button and the localizer was captured this time (3rd image).

                                            Just as I crossed CEPIN at at 3000 ft, descending towards 1800 ft. at AXMUL, the magenta G/S diamond appeared (4th image)

                                            Bill Clark


                                            Vectors.jpgOver wrote Vector with DUMBA.jpgLocalizer Capture.jpgGS Capture.jpg
                                            Last edited by Bingo041; 19Sep2020, 21:54.
                                            Bill Clark
                                            Win10, V-2004//I5-8600K 5.2GHz//Nvidia GTX 1080Ti//VRAM 11GB
                                            RAM 32GB//2TB M2.NVMe//Gigabyte Z370 Gaming 7//Corsair H115i

                                            Comment


                                              #24
                                              That looks good Bill, note that ARCHI is available as an approach transition which makes the need to create a path unnecessary. Also, when I have a good G/S indication and I'm below it (as expected) then I will switch to V/S pitch mode and descend at perhaps 500 fpm to allow the G/S (which descends at about 800 fpm depending on ground speed) to reach me before the FAF. The VNAV PTH will generally not intercept G/S until FAF and I prefer to be on an an establish final descent in the B748 a little earlier.
                                              Last edited by DDowns; 19Sep2020, 22:20.
                                              Dan Downs KCRP
                                              i7-10700K 32GB 3600MHz 1080Ti

                                              Comment


                                                #25
                                                Dan,

                                                Looking at the chart, ARCHI is another choice I could use.

                                                Using V/S to capture the G/S sooner is a great tip.

                                                Would it be better to use HD SEL and FLCH from ARCHI to capture the LOC first?

                                                I haven't flown the 747-8 for about 4 months as I was on DCS developing missions, but it seems like I used to capture the G/S prior to CEPIN, just can't remember for sure?

                                                Thank for your help,
                                                Bill Clark
                                                Bill Clark
                                                Win10, V-2004//I5-8600K 5.2GHz//Nvidia GTX 1080Ti//VRAM 11GB
                                                RAM 32GB//2TB M2.NVMe//Gigabyte Z370 Gaming 7//Corsair H115i

                                                Comment


                                                  #26
                                                  Originally posted by Bingo041 View Post
                                                  Dan,

                                                  Looking at the chart, ARCHI is another choice I could use.

                                                  Using V/S to capture the G/S sooner is a great tip.

                                                  Would it be better to use HD SEL and FLCH from ARCHI to capture the LOC first?

                                                  I haven't flown the 747-8 for about 4 months as I was on DCS developing missions, but it seems like I used to capture the G/S prior to CEPIN, just can't remember for sure?

                                                  Thank for your help,
                                                  Bill Clark
                                                  The use of HDG mode to intercept LOC is a simulatorism, used to solve the problem of a LNAV track not aligning with the LOC. My own procedure is to use it by exception. I am familiar with locations in the simulator world where it is required but in general will use LNAV and monitor the LOC deviation. If the LNAV path starts turning me to the final course before the LOC is captured then intervention with HDG mode is used.

                                                  FLCH descent is used when you want an aircraft to descend expediently to a lower altitude. The thrust will retard to idle and the pitch mode will sustain the VNAV SPD (or MCP SPD if intervening) at whatever rate of descent is necessary for that speed unless the aircraft is within a certain range of the MCP ALT. I prefer to use V/S in these cases because I usually want to control the rate of descent, especially when I just a few miles from final approach intercept. With V/S mode you descend at the rate you set at the speed you set.

                                                  Dan Downs KCRP
                                                  i7-10700K 32GB 3600MHz 1080Ti

                                                  Comment


                                                  • Michael Codd
                                                    Michael Codd commented
                                                    Editing a comment
                                                    As I previously indicated, it is common practice to use HDG SEL in the real world B744 to intercept an ILS LOC, so it should definitely not be regarded as a 'simulatorism' (whatever that means!🤔).

                                                  • DDowns
                                                    DDowns commented
                                                    Editing a comment
                                                    Interesting... thanks.
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