VGP: have you used it?
#22
Gets Weekends Off
Joined APC: Jul 2013
Posts: 459
The method of flying the approach doesn't determine the minimums (DA or MDA). It is the approach type that determines either a DA or MDA. If the approach is an APV, Approach with Vertical Guidance, then a DA may be used, in fact, it is published. The only APV approaches I'm aware of are RNAV (GPS) to LNAV/VNAV minimums, LPV approaches, and RNAV (RNP) approaches. All other Non-xLS approaches are Non-Precision approaches with a horizontal ROC which requires an MDA. To use a DA in lieu of an MDA for these approaches requires OpSpec C073.
Further, MDA is generally no longer used when using CDFA method. Typically a Derived Decision Altitude is set 50' above MDA, for the decision point to land or go around.
Further, MDA is generally no longer used when using CDFA method. Typically a Derived Decision Altitude is set 50' above MDA, for the decision point to land or go around.
#23
Line Holder
Joined APC: Mar 2012
Posts: 41
Airbus calls this the FLS for "FMS Landing System". It generates an FMS-derived glidepath and extended final approach course based on whatever nonprecision approach is in the box. You DO, in fact, press the APPR button to arm it, and it arms and captures modes called F/LOC and F/GS (FMS Localizer and FMS Glideslope). Can join off the LNAV course or a heading, just like a regular ILS.
In fact the deflections are displayed on the PFD (and ND if so selected) exactly like a regular ILS but using double diamonds for the "needles". The FMS signal is actually routed through the same multimode receiver that processes conventional Localizer and Glideslope signals, which then displays the ILS lookalike indications.
Works wonderfully and completely replaces the FINAL APP mode in aircraft so equipped.
In fact the deflections are displayed on the PFD (and ND if so selected) exactly like a regular ILS but using double diamonds for the "needles". The FMS signal is actually routed through the same multimode receiver that processes conventional Localizer and Glideslope signals, which then displays the ILS lookalike indications.
Works wonderfully and completely replaces the FINAL APP mode in aircraft so equipped.
#24
On Honeywell Apex avionics we use Approach mode for all "Localizer" type approaches; ILS, LOC, LPV, LNAV/VNAV. During last recurrent I asked about LNAV/VNAV to verify and was told yes.
#25
The FMS VNAV path starts from 50" above the first brick of the runway and is only concerned per ARINC 424 to clear obstacles from there to the FAF. If there are no terrain or step down problems in the final segment then the angle will be 3 degrees. If there are obstacle factors in the final segment then the VNAV path will raised to clear them to a limit of 3.8 degrees "if I remember right from my FMS coding days". I.E. you are only guaranteed step down clearance inside the FAF. There is a new generation of approaches being tried out where the VNAV path will clear all step downs further out. I think you will have to activate approach mode or equivalent at a certain point.
A little light reading
https://www.faa.gov/documentLibrary/..._Circular/AC%2
090-105.pdfhttps://ieeexplore.ieee.org/abstract/document/5347485/?reload=true
ARINC 424 Navigational Data - Jeppesen
A little light reading
https://www.faa.gov/documentLibrary/..._Circular/AC%2
090-105.pdfhttps://ieeexplore.ieee.org/abstract/document/5347485/?reload=true
ARINC 424 Navigational Data - Jeppesen
#26
If we are talking about ARINC coded VDAs -calculated glidepaths for NPAs, they DO NOT provide any obstacle clearances between the FAF and the MAP. They are strictly mathematical computations for a TCH and FAF altitudes giving a coded angle for a displayed glidepath.
#27
I just checked with a old friend who still codes FMS Navdata and ARINC 424-19 spec is to go from 50' above the runway to the FAF and make the VNAV angle clear any step downs between the FAF and the 50' crossing height.