Modern IFR Navigation: Difference between revisions

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(Cquoting some of the discussion on the mailing list)
 
(make this article --only-- about navigation, move MFD stuff to complex canvas avionics)
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This article is about the discussion which followed that message, which focused heavily on modern IFR navigation.
This article is about the discussion which followed that message, which focused heavily on modern IFR navigation.
== Making an MFD ==
{{FGCquote
|1=
Note that this isn't just a matter of throwing up a canvas showing some GPS waypoints and a magenta line. Modern navigators are astoundingly-complex
devices — probably an order of magnitude more lines of code than FlightGear itself — and even their basic flight planning algorithms and databases (e.g. fly-by waypoints vs fly-over waypoints, open vs closed approach procedures, transitions into RNAV approaches, etc.) are far beyond the scope of anything we've tried, and we'd also need an up-to-date database far more complex than the ones we have now. Once you get to the extra features, like FIS-B weather or TIS-B traffic info over ADS-B, or TAWS (terrain alerting), we're probably in way over our heads trying to emulate even the simplest general-aviation IFR GPS.
|2= {{cite web
  |url    =  https://sourceforge.net/p/flightgear/mailman/message/35924395/
  |title  =  <nowiki> [Flightgear-devel] RFD: FlightGear and the changing state of air
navigation </nowiki>
  |author =  <nowiki> David Megginson </nowiki>
  |date  =  Jul 3rd, 2017
  |added  =  Jul 3rd, 2017
  |script_version = 0.39
  }}
}}
{{FGCquote
|1=
As I tell my students in real life:  Don't get intimidated or hypnotied by the huge number of features. 90% of the value comes from 10% of the features. Actually that's becoming more and more of an understatement. With rare exceptions, you can ignore the features you're not using. This is relevant to FG in the sense that it is not important to implement all the features.  Most can be left out in the short term, and some can be left out forever.
|2= {{cite web
  |url    =  https://sourceforge.net/p/flightgear/mailman/message/35924414/
  |title  =  <nowiki> Re: [Flightgear-devel] RFD: FlightGear and the changing state of
air navigation </nowiki>
  |author =  <nowiki> John Denker </nowiki>
  |date  =  Jul 3rd, 2017
  |added  =  Jul 3rd, 2017
  |script_version = 0.39
  }}
}}
{{FGCquote
|1= I think there has been some development in this area for some time, but it's not clear how complete it is in terms of going beyond a PFD displaying basic flight information digitally.
For example zakharov on the forum has been developing a Garmin G1000 clone called the zkv1000:
https://forum.flightgear.org/viewtopic.php?f=14&t=32056
The DA-42 model uses some form of G1000 as well - which may be an older version of the zkv1000.
I agree that this is something we need to address, as our GA aircraft will otherwise become more and more old-fashioned.
I'm more optimistic than David - I think we do have the capability to write this - for example just look at the complexity of the Shuttle model.
|2= {{cite web
  |url    =  https://sourceforge.net/p/flightgear/mailman/message/35925226/
  |title  =  <nowiki> Re: [Flightgear-devel] RFD: FlightGear and the changing state of
air navigation </nowiki>
  |author =  <nowiki> Stuart Buchanan </nowiki>
  |date  =  Jul 3rd, 2017
  |added  =  Jul 3rd, 2017
  |script_version = 0.39
  }}
}}


== Advanced RNAV Approaches ==
== Advanced RNAV Approaches ==

Revision as of 08:55, 6 July 2017

On July 3d, David Megginson wrote to the mailing list,

Cquote1.png The airspace system is in the process of changing drastically, and I'm following it this summer by finally biting the bullet and installing an IFR GPS (Garmin GTN 650) and ADS-B transponder (Garmin GTX 345) in my Piper Warrior II. What this means that for the first time in the 15 years since I started flying in real life, I won't be able to use FlightGear to practice the IFR approaches I'm flying in real life.
 Cquote2.png

This article is about the discussion which followed that message, which focused heavily on modern IFR navigation.

Advanced RNAV Approaches

In the modern world, RNAV approaches are a lot more complex than following a magenta line and manually calculating a vertical speed or using VNAV. Modern RNAV approaches involve things such as "radius-to-fix" segments, which allow curved paths around mountains, which the aircraft can follow. One example is the RNAV (RNP) Y to 05R at Auckland: http://www.aip.net.nz/pdf/NZAA_45.3_45.4.pdf.

Cquote1.png One thing that is very important moving into the future is the RF approach (radius to fix). Please read this: https://en.wikipedia.org/wiki/Performance-based_navigation#RNAV_and_RNP_specific_functions... This style of RNAV approach is becoming more and more common, and FlightGear cannot yet simulate it.
 Cquote2.png
Cquote1.png DME arc transitions still exist, and I enjoy flying them both in FlightGear and in real life. There are two important differences for the radial-to-fix transitions (as I understand so far, still studying up the new-to-me RNAV procedures):
  • You can fly them around any fix, not just a DME/TACAN (typically colocated with a VOR). Granted, you could do that in FlightGear now simply by using the GPS distance, but ...
  • The CDI actually gives you (and the autopilot) guidance for where you should be flying, so you're not manually estimating your course based on the DME/GPS distance while flying 90° to the navaid bearing.
It's the second one that will trip us up for using FlightGear as a way to practice modern IFR procedures.
 Cquote2.png
Cquote1.png Are you wondering about the math to give you a guidance target for flying around a given point? Or are you wondering how to render the 'fly-to' indicator?

The first basically is the same as the Shuttle HAC intercept where Rdot (the derivative of the radius to the center point) in combination with R can be used as error for guidance and the second depends on your particular instrument - the Shuttle HUD shows a corresponding indicator (and so does the PFD) - but I suspect the instrument of choice of a GA aircraft will display it differently.

So this should be possible to code by any aircraft maintainer without much fuss as far as I can see.
 Cquote2.png
Cquote1.png The Route Manager should be able to handle most of the "magenta line" tasks, but it may be that the more complicated routing such as the RF approach, fly-by vs fly-over requires some new autopilot coding as you describe.
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