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Waypoint

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Background

In real life, there are different types of waypoints: "fly-over" vs. "fly-by" - check out the FAA's "Instrument Procedures Handbook" App. A, p6: http://www.faa.gov/library/manuals/aviation/instrument_procedures_handbook/media/APPENDIX-A.pdf

n real flight management systems, there are additional waypoint constraints possible. Such as for example altitude constraints to indicate max/min altitudes for passing a given wpt.

With Boeing aircraft, this can be configured using an optional suffix behind altitudes, such as "A" for "this altitude or above" or "B" for "this altitude or BELOW".

For example: SFO@5000A would mean "pass SFO fix at 5000 ft or above", while "SFO@5000B" would mean "pass SFO fix at 5000 or below".

This could probably be implemented just by having two additional autopilot modes for climbs/descent "at-or-above" (minimum altitude) respectively "at-or-below" (maximum altitude) so that the altitude change is guaranteed to take place with a gradient that ensures the constraint is made.

Also, flight levels can often be directly specified using the "FL" prefix, eg "FL210" (but that could also be just implemented in future CDU implementations that internally convert everything to ft).

Path Terminators

In real life, instrument procedures are defined and stored in navigational databases that internally use the ARINC 424 format. ARINC 424 uses the so called path/terminator concept, to define legs:

Path Terminator concept

  • Transforms procedures into coded flight paths
  • Set of two letters
  • PT instructs to navigate from a starting point
  • to a specific point
  • or terminating condition

(see: http://www.acac.org.ma/Ateliers/6.ppt )

ARINC 424 Path & Terminators (short considerations)


Description of Leg Types introduces the ‘Path/ Terminator’ Concept:

  • Path – logically describes how the aircraft gets to the Terminator (track, course, heading);
  • Terminator – is the event or condition (fix, altitude, distance, manual) that causes the system to switch to the next leg;

(see: http://www.ecacnav.com/downloads/7_The% ... pplier.ppt )

Status

Cquote1.png James has done a lot of work recently on the route manager, to support these different kind of waypoints, turn prediction etc. I don't know whether the A330 makes use of it (I remember some of the Airbuses using a Nasal system), but if it does it should have that working in 3.4.
— Gijs (Feb 21st, 2015). Re: A330-200 with Canvas and other features.
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Development

Cquote1.png the existing waypoints don't seem to contain enough information, I've written some more Nasal classes to handle SID/STAR/IAP, Top of Climb and Top of Descent pseudo waypoints and Altitude constraints versus FMS calculated altitudes etc.
— scotth1 (Jun 21st, 2011). Re: ND prototype (not even in Git, yet).
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Cquote1.png I don't want to hard-code that kind of logic in C++, if I can avoid it - but we need to work out a way for Nasal to set the values into the route-manager or GPS data, so the ND can pick it up - especially all the cruise/phase-of-flight/altitude/energy stuff. I apologise for being lay, but can you remind me where the relevant Nasal code is? Then we can have a discussion (possibly involving some other people) about which parts can be in C++, and some standard locations the ND can look for Nasal-computed value, and so on.
— zakalawe (Jun 21st, 2011). Re: ND prototype (not even in Git, yet).
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Cquote1.png Due to the waypoint transition system being really picky on getting to the waypoint, I've wrote a different nasal transition system for my aircraft (A320neo, A330-200s and -300s) which simply increases transition range. The 2 different GPS accuracies on those aircraft let you go on to the next waypoint a little before you get to the current one.
— omega95 (Dec 28th, 2012). Realistic waypoint transition system.
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Types of Waypoints

Fly-by

Fly-over