I’m working on procedure building, and trying to understand this: why is there typically a center waypoint (usually of the runway, the airport, or a navaid on the airport) used at the FAF / FAP, even when that segment is not an arc? The developer docs don’t cover this from what I can find, nor does the ARINC-424 documentation I’ve reviewed.
I’m having an issue on my procedure where the lateral pathing works perfectly, but the VNAV path breaks at the FAF, no glidepath angle is specified in the FMC even though it’s specified in the data for every leg from the FAF to the runway, and though the runway is specified in the navdata, in the FMC the airport ID is used instead as the end of the approach / the MAP. I’m obviously missing something; wondering if this center waypoint for the FAF is related.
Hi,
I’m not sure what dataset you are using nor do I see any example. At least an example would hel - which airport, which procedure and also which ARINC424 version you use as your source?
Thanks very much for the reply. You’re right, I could have provided more detail, sorry. I’m working with the new PMDG navdata, which seems to be the standard DFD format?
As far as an example of what I mean, it seems any RNP approach has something - runway, airport or on-field navaid - as a center waypoint in the record for the final approach point. The PANC RNAV33 and the VNKT Rnav 02 (I think the Z approach) are a couple examples of procedures where the leg to the FAF is a TF leg, but the runway or airport are still used as a center waypoint. (If the leg in question is an RF leg, then the center waypoint used is the center of the arc like every other RF leg, so that makes sense.).
As far as an example of my procedure, that’s a little trickier. It is a real-world but non-public procedure; to post it I’d probably have to obfuscate waypoint names/coords, but as the lateral path is not the problem that would probably be ok. My overall problem is that even though the FMC recognizes it as a selectable approach with the defined transition, the FMC doesn’t seem to recognize it as having a final approach segment - the VNAV path disappears at the FAF and there’s no runway waypoint but instead the airport (PAJN).
But one thing at a time I guess; I’d like to understand the use of these center waypoints on non-RF segments. This stuff is fascinating; I’ve been flying them for years but it’s really interesting to see the data behind them and to build one into the sim. I know this isn’t really the intent of the forum here, so I really do appreciate any time you take to explain this or point me to the relevant documentation. Thanks again.
There is no use of a center WPT outside of an RF-Leg in ARINC 424 SID, STAR or Approach records.
Looks like its just the pointer to the MSA (APT, RWY, Navaid, WPT) used for that procedure. But it has no impact on the aircraft. You should be able to leave it blank since its up to you to specify an MSA or not for a tailored procedure.