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GAJ52

EGKK LAM4M Problem

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I posted this in the PMDG forum but was advised to request help here.I have loaded up the latest EGKK SID's from Planepath in to my PMDG 737-800 and have selected the LAM4M sid from runway 26L. I can see the first fix (IWW2.3) in the FMS Plan screen but the magenta line does not fly over it. The IWW2.3 is the first turn point after takeoff but the aircraft follows the maganta line and turns too early. I have LNav selected and the autopilot in command mode. Any ideas why its not waiting for the IWW2.3 fix before it turns to the right. It can't be following the HDG bug because this is set to 260.I'm also having the same problem with the latest Navdata SIDGlen

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Hi there Glen,I think I know what is going on. Some background so we are on the same page. There are two types of waypoints, fly-by and fly-over. The fly-by means the aircraft will turn before it reaches the waypoint in order to be on course for the next leg. The fly-over means the aircraft has to fly over the waypoint before it is released to go to the next waypoint. This usually results in an overshoot where the plane has to fly a correcting course to get back on the next leg course line.Now this all leads up to what you are seeing. The default rule is to use fly-by unless the waypoint is specified as a fly-over. With that in mind the reason, I think, that the first turn is before getting to IWW23 is because of the fly-by rule. The plane is turning early in order to try and roll out on the next leg course line. Now having said that I think I will change the procedure and make IWW23 a fly-over because after rereading the narrative section of the SID it is implied that it is a fly-over.Thanks for bringing this to my attention. The changes will show up in the next cycle because I need to have a look at all the EG-- procedures. If you would like to make the change yourself now then do this.Open the EGKK.txt file and find the "FIX IWW23" in the line below "SID LAM4M FIX LAM 6000". Change "FIX IWW23" to read "FIX OVERFLY IWW23" which makes the waypoint a fly-over type waypoint. Save the file and go fly. The plane will now fly over IWW23 before turning.RegardsTerry

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I can confirm this IS down to FLYBY vs FLYOVER waypoint settings, Terry - and it's a regular issue with many UK airports.However, I tend to think of it as a pilot-responsibility issue, rather than something we can expect the FMC to get right 100% of the time.Reason being, some planes (such as those by PSS) simply don't have any way at all of denoting FLYOVER in the loadable procedures (though it IS possible to mark them as such, via the FMC, only after the proc is loaded up, using the OVFY triangle button - and I think the PMDG has something similar, too).Certainly it would be great if you can incorporate FLYBY/FLYOVERness in the PMDG data, and the other types that can handle it in the proc code - but be aware (if you're not already) that some of the UK SIDs are NOT clearly defined on the charts alone, and refer also to the Noise Abatement Procedures (which they usually incorporate) given in the AIP Textual Data sections for each given airport. A common 'brickbat' you'll encounter is those initial climbout waypoints that are 'X DME at or above Y thousand feet' (ie, fixed distance with minimum height), and those which are 'no turn before Y thousand feet or X DME, whichever is the earlier' (ie, more like a climb-to-alt leg, but with min distance if that height is not met in time).From experience, they can be a real pig to code, even on PMDG, because there's not an exact rule to handle that particular combination of restrictions! In those situations, the fact that the initial waypoint is NOT necessarly fixed as a FLYOVER actually means the plane turns more appropriately (as per the real world) than it would if the point was marked FO. Of course it varies, though, so it'll be a lot of work to cross test it all (and of course, I'm willing to do my bit when and wherever I can).For that reason, I always think it's still a good idea for a pilot to approach things from a 'do I need to alter any constraints or mark a FLYOVER waypoint here or there?' perspective, and not rely wholly on the FMC proc to get it 100% right every time. I'm sure in the real world something similar happens, too, so it ain't so bad ;)Regards

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Terry,Many thanks, I have modified the sid as per your example and it now works as expected.Glen

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