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Wrong turn on intercept

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Good afternoon

 

Some SIDs include a turn to intercept a radial or track where the turn is not executed in the shortest direction, but the opposite, leading to a turn of more than 180 degrees. Reason for this "loop" is mostly noise abatement. Examples are NORDI 1D in Larnaca (LCLK) or ALBIX 1R in Zürich (LSZH). Unfortunately, the 777 does a straight left turn in the Larnaca example, not flying the 240 degree loop to the right, but a 120 straight turn to the left. In the Zurich example, the ND flips back and forth between a left turn loop and a straight right turn, until it finally decides for one option or the other after takeoff.

 

How to deal with this. if it is a problem with the Airac data, can this be corrected with manual entries in the FMS LEG page? Does the Airac even carry the necessary information?

 

Thanks

Peter

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Amazing how realistic PMDG made this simulation, lol.

 

Years ago we had this exact problem on the real 777.......airplane would make the initial departure turn in the wrong direction with Lnav.

Not allways....but under certain conditions and I dont remember them exactly.

A service bulletin was issued by Boeing with instruction of how to prevent the issue untill the FMC coding was fixed in the next update.

 

Using heading select (not arming Lnav) to get the airplane to turn in the right direction and thereafter engaging Lnav would fix the problem.

An other way would be to create a waypoint on the legs page to make sure the airplane turns in the correct direction......but this is not ideal as it could screw things up even more causing noise abatement violations etc.

 

I am not sure if in this case the FMC programming by PMDG is at fault and a bug should reported to them.....or that the Nav Database you use is at fault.

 

What navdata do you use?

I use aerosoft......if you use a different database then I can test as well and see if it is FMC coding or database coding!

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I am not sure if in this case the FMC programming by PMDG is at fault and a bug should reported to them.....or that the Nav Database you use is at fault.

 

The problem, in my opinion, is we have not yet been able to migrate to the same data format as used by FMS i.e., ARINC-424, which would be much more powerful than the simple text-based 'macro' language that we use now.  On the plus side, the macro language is easy to learn and one can create and modify their own terminal procedures. On the minus side, there are many things, like RF legs, than can only be approximated.  The big obstacle is price. PMDG has looked for a reasonably priced source for this data but so far nothing has turned up.

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The problem, in my opinion, is we have not yet been able to migrate to the same data format as used by FMS i.e., ARINC-424, which would be much more powerful than the simple text-based 'macro' language that we use now. On the plus side, the macro language is easy to learn and one can create and modify their own terminal procedures. On the minus side, there are many things, like RF legs, than can only be approximated. The big obstacle is price. PMDG has looked for a reasonably priced source for this data but so far nothing has turned up.

Interesting....I allways ignored all that Airinc stuff in our study material because it is just too much......or not enough maybe as I hate it when a subject is only touched at the surface and I still understand nothing of it.

 

So for me to read that PMDG has even gone through the trouble of trying to understand and simulate the real Airinc system (even if that ended up as not feasable) is quite impressive!

 

I like the text base system though because, as you said, it can be easily adapted.

Even I was able to do that!

And others have made Rnav approaches into KaiTak :-)

 

I actually even like it when the (simulated) system does not allways do what it should do.

You are not supposed to blindly follow the FD.....if it does not do what you want it to do in Lnav, then choose another mode that does.....keeps you on your toes these little quirks ;-)

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Thanks a lot for all your insights. I now understand that this is a data issue - i.e. the necessary information is not available to the FMS. Is it possible to rectify this myself by correcting / amending the waypoints on the LEG page after first having selected and activated the respective SID?

 

- Peter

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Thanks a lot for all your insights. I now understand that this is a data issue - i.e. the necessary information is not available to the FMS. Is it possible to rectify this myself by correcting / amending the waypoints on the LEG page after first having selected and activated the respective SID?

 

- Peter

The best thing to do, in my opinion, is to fly the airplane first. For example, use MCP HDG instead of LNAV on departure and use HDG to commence your turn. As you roll out on your initial heading towards the next fix you can then set up LEGS page by double clicking the LSB next to the fix and EXEC then engage LNAV to follow your magenta line.  It is okay to fly off of the magenta line.

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PMDG has looked for a reasonably priced source for this data but so far nothing has turned up.

 

That's interesting because the data (RF fix, multiple ILS per runway) is available from Navigraph/Jeppesen (and Aerosoft/LIDO) is is used in the AIRAC's they provide for aircraft capable of using it.  At one point PMDG had said they would be implementing advanced navigation features but apparently other development got in the way.  At any rate, using the raw  ARINC-424 format would be a nightmare from both the parsing and performance standpoint - consequently we have tailored databases.

 

DJ

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raw ARINC-424 format would be a nightmare from both the parsing and performance standpoint

 

And that is interesting because the data is readily available from the FAA and is used by many commercial operators.  The problem as I understand it is that the information is not available globally at a reasonable price.  I do not speak for PMDG, but this is a subject that I am very interested in and have spent years playing with 'navdata' so when someone claims that ARINC-424 is available for a reasonable price you've got my attention. Show me.

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Dan,

 

I never said the raw AIRAC-424 data is cheap.  I said the data necessary  to implement the features I mentioned above is available from LIDO and NavTech and is used in datasets provided by Navigraph and Aerosoft.  The lack of the raw ARINC is not, or should not, be an issue for PMDG since other developers have been able to get the data they need implemented.  The ARINC spec is available (as I recall) for around US $250 the last time I looked, and the spec is all that is needed to develop for the implementation.

 

ARINC data as used by operators has been rebuilt into a more usable format for speed and a great deal of the miscellaneous data has been removed - very like the datasets we use for FS.

 

DJ 

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