Peter wrote:
+V merely clears all obstacles between FAF and MAP.
Peter,
The +V advisory glidepath is constructed by the manufacturer of the database drawing a line between the FAF at its minimum crossing altitude to the the runway threshold at an altitude of the crossing height. It is nothing more and nothing less. It will pass thru the MDA at roughly the point that on US charts show a Visual Descent Point (VDP) V symbol. It has not assurance of obstacle avoidance beyond the VDP point or anytime below the MDA. An officially vertically guided procedure on an APV provides clearance to the runway and is evaluated by the state, not the manufacturer.
So, AIUI, both LNAV/LPV and LNAV/VNAV are obstacle-cleared all the way to the tarmac?
Anders wrote:
But it seems strange that there is no better way of knowing if you should plan to use the LNAV/VNAV minima or LNAV minima.
When you select the approach, it will display the minimums that will be available. This is true for the GTN and the GNS. The GNS shows it on the select approach dialog map. If you want to check, ou can go thru the selection process for an approach at any time, but just cancel out of the selection once you have obtained the annunciation information you were looking for,
If you have a current database in one of the simulators, you can check at home.
Peter wrote:
So, AIUI, both LNAV/LPV and LNAV/VNAV are obstacle-cleared all the way to the tarmac?
No such thing as an LNAV/LPV, but if you restate to “AIUI, both LPV and LNAV/VNAV are obstacle-cleared all the way to the tarmac?” the answer is yes and this is accomplished by the state authority when they evaluate and design the procedure.
Edit: I make one proviso, you remain on the course centerline and GS as there can be obstacles off to the side.
In other cases, specific approaches may not be coded for LNAV/VNAV because of software issues in the Garmin equipment. The RNAV (GPS) RWY14L at EDDK is an example of an approach that Garmin had an issue with because the final approach course is 7.0 NM or greater.
Is that a typo? Do you maybe mean they had a problem and couldn’t code it to be an LPV?
As an aside, the FAA is getting more involved with +V, even though they don’t design the approach with this in mind. The +V path is now evaluated on new LNAV approaches by flight test. They fly the approach one dot below the potential +V and if there are any deviations required in the flightpath to avoid obstacles, the flight test report indicates that the approach is not suitable for +V. This results in the Visual Descent Angle and TCH being removed from the chart and a note being added that used to state “Descent Angle – NA” and now states “Visual Segment – Obstacles”. With thousands of approaches already published, it will take years before those approaches that now have +V will all be evaluated and have the +V removed from the database.
NCYankee wrote:
Any state can determine what the permissible criteria are for an LNAV/VNAV procedure. It appears that some states have effectively banned them using a WAAS GPS for the vertical on LNAV/VNAV approaches.
I know that Germany explicitly allow EGNOS to be used for vertical guidance on APV-Baro / LNAV/VNAV approaches. See the excerpt I added in my original post, post #1.
And then the guys running EGNOS say that there are 69 EGNOS enabled APV-Baro approaches in Germany. I would like to know which they are. I have loaded a few on the GTN650 but so far I have only got a LNAV annunciation. I have a feeling that you in reality will only get LNAV annunciation for any LNAV/VNAV approach in Germany.
Flyer59 wrote:
Is that a typo? Do you maybe mean they had a problem and couldn’t code it to be an LPV?
No. The charted procedure does not have an LPV, but it does have an LNAV/VNAV. My point is that this procedure has a final approach segment that is 7.0 NM or greater and therefore when Jeppesen makes the database record for that procedure it can’t be coded as an LNAV/VNAV. This was caused by a software error detected many years ago and since resolved, but it is not clear if the database has been updated to take advantage of the fix. It is also not clear if all GNS/GTN/G1000 systems have been upgraded to have the fix. The error was that the lateral CDI full scale deflection (FSD) on the WAAS systems was +/- 2 degrees for the final approach segment. At 6.95 NM, FSD is 0.3 NM wide. This made the CDI FSD greater than 0.3 NM when the final approach segment is 7.0 NM or greater, but the LNAV/VNAV FSD is not permitted to be greater than 0.3 NM. The final approach segment for the EDDK is 8.5 NM. Garmin’s solution is to only code the approach in the database as LNAV using a maximum FSD fixed at 0.3 NM, thus losing the LNAV/VNAV capability.
That means, although published I might arrive there and not get the LNAV/VNAV right?
Flyer59 wrote:
That means, although published I might arrive there and not get the LNAV/VNAV right?
Yes. You can check on your GNS in the airplane or using the simulator at home. PM me.
