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FMC data, LNAV/VNAV apps and DME ARCS

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Hi AllDoes anyone know if the current FMC programme will be updated to include proper DME arc's without having to make up lots of points. and slope guideance to allow the flying of RNAV approaches using LNAV/VNAV (Boeing) and Fully Managed Approaches (Airbus)I find these to be the two main missing factors in the writing code of the current programme.CheersDavid


David Cook

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Guest M-Sauce

It does allow VNAV approaches, I do them all the time. Select non-ils approach from the FMC DEP/ARR page. You will notice that if the missed approach point is before the runway, there should be a glidpath angle on the right hand side of the legs page, by the Airspeed/Alt constraint entry. When flying the approach, obviously you should be in VNAV mode. You can try this with an ILS approach, just don't select APP on the MCP. Rather arm the LOC and then use VNAV for the descent. Once the first fix of the approach cycles, you will be able to open the speed window and control speed while the aircraft flies the path. You should see these FMA modes SPEED | LNAV (or whatever else you are using | VNAV PTH. If the vertical mode switches to VNAV SPD then you opened the window too soon. You must make sure that the altitudes are programed correctly and that all the modes are entered correctly. I can't teach you that, but I asure you, I've been flying VNAV approaches on the 73 and 74 since I bought them both. I must say, the VNV on the 73 is quirky and not foolproof, but it does the job somewhat decently. Hope this helps.Mariano

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DME arcs do not exist in the real FMC database... the pilots have to build them with custom place/bearing/distance waypoints.As stated, we do in fact already support VNAV approach guidance.


Ryan Maziarz
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Hi RyanThanks for your reply, however DME arcs do appear in real FMC/FMGC databases. What we really need is coding that allows an arc to be drawn properly between two points not lots of P/B/D which is actually unrealistic under normal operations.I know that the VNAV works at the moment, particularly in the 747 but I was wondering if the A320 fully managed approach function will work correctly. What I'm eluding to is coding that allows a slope value to be entered in the proceedure when it is written, giving actual slope guideance not just a line between two heights, if you know what I mean. OK, thanks againDavid


David Cook

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The ARINC RF (radius to fix) isn't supported. We're hoping that the new stuff they are working on will be a lot more current in this area. The VNAV especially needs work.On the plus side, the sidstar & airac data files are in a language or construct that is very easy to work with... facilitating lots of contribution from the community. There are workarounds to arcs, procedure turns and even parallel entry to holding that can be easily written... just can't make the VNAV do much more than it does.


Dan Downs KCRP

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DME arcs are certainly in our database. I cant think of a reason why they wouldn't be in UAL's. One of the RW limitations of the DME arc approaches is that you can only join them at a preprogrammed position on the arc (ie off an inbound rte). This can be a nuisance if being radar vectored or tracking to a different place on the arc that is avaialable for selection in the FMC. This can be overcome by entering the arc app, EXECuting it but leaving the RTE discontinuity in there. Do not join up the gap between the point before the arc and the TO point on the arc. Use heading select to maintain trk to the arc. Arm LNAV. LNAV will automatically capture the arc and fly it the correct way, even if when approaching the arc the active waypoint is showing in the opposite direction. When LNAV engages it will change the active waypoint to the next one on the correct side. Magic bit of kit.I agree with the points raised above that the code needs to be looked at to facilitate easier writing of SIDs, STARS etc. VNAV also needs a tweak, especially in the area of eng out and missed approaches. VNAV also does not work correctly for descents or VNAV approaches.


Cheers

Steve Hall

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Hi AllThe FMGC handles the arc in much the same way as you describe Steve, except we have to clear last and next waypoints to force the first waypoint in the correct direction of turn to be the active.To me the FMC/FMGC is the heart of the aircraft and for PMDG to truly have the greatest product the programming of these needs to be better. Don't get me wrong I think all PMDG products are the best, they have got the visual model and systems to an excellent level, it just needs to be topped off with better detail in the FMC/FMGC area.With the increasing use of RNAV and RNP approaches it would be wonderful to have a simulation that can represent these ever more common proceedures perfectly. This is particularly the case with curving (arc) arrival segments for example NZQN (see attached link if I got i right)http://www.aip.net.nz/pdf/NZQN_45.3_45.4.pdfSteve, I have completed a major rewrite of the NZAA (Navdata) arrivals and approaches, including the RNAV approaches, it seems to work pretty well now in LNAV/VNAV with the 744, the 737 is not so good. Let me know if I have made any mistakes.CheersDavid


David Cook

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David,Just as a side note. Your linked procedures for Queenstown did not seem to contain any arc segments. Just nicely curved lines. How do you program those without a radius or centre?See UME DME ARC 12 on the below chart. The segment starts at UME radial 029 and ends at UME radial 323. The radius is 12 nm and the centre is VOR UME.http://www.lfv.se/upload/ANS/AIP/AD/AD2/ES...ESNU_4_5_en.pdfCheers,


Mats Johansson
PMDG Flight Test Dept
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>DME arcs are certainly in our database. I cant think of a>reason why they wouldn't be in UAL's. They aren't in Varig's 777s either. At least they weren't since Varig, Alas, is no longer.edit: forgot to sign!Godspeed,Victor


Cheers,
Victor M. Lima
 

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David I agree with you with respect to the need to update the PMDG FMC programming. The accuracy of the FMC reproduction and the ability to fly common place RNAV approaches will be a defining point for FS add ons. 90% of the FMC works very well and is reproduced very accurately which unfortunately has a downside when you strike something that is glaringly wrong. NZQN is one of many airports now using curved segments for both arrivals and departures. There is a work around, as Dan has pointed out, but this involves the addition of many waypoints (the closer together the more "curved" the track) but this can become a little confusing when attempting to monitor the approach.Where is your NZAA file? Is it on the NAVDATA site?Ray Lang has produced some RNAV arrivals for NZQN and can be downloaded from here: http://www.vatnz.net/cms/index.php?option=...id=37&Itemid=33


Cheers

Steve Hall

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Hi AllMats, I included the link to NZQN as an example of the future of RNAV/RNP. Your example is of course a normal DME arc centred on a navaid, which is easily made up using P/B/D but is actually not realistic, compared with the arc selected in the FMC/FMGC. The NZQN RNAV/RNP is vertually impossible to model correctly, made worse by the poor VNAV of the 737.Steve, my NZAA is on Navdata, or is attached if I got it right (again)CheersDavid


David Cook

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David I have yet to fly your NZAA SIDS/STARS procedures although I have had a look thru it. Do you find that the AT or ABOVE 4000 SPEED 220 works? I have found that the speed will only be flown if coded against a hard altitude ie. AT 4000 SPEED 220.


Cheers

Steve Hall

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Guest stew286

hi dave 05 looks very tricky especially in low viz.stu

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SteveYou are right it does not work, might have to change that to 4000 SPEED 220.I am having trouble with speed at other places to, like NOKAM SPEED 210 and BERMA SPEED 210.Any advice?David


David Cook

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