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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).
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
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 )
|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.