Peter wrote:
Can’t you fly the enroute sector and then continue to a +V descent, like a normal GPS approach?
On NPA, you could hit “+V FAP” (point where +V touches the platform altitude) few nm before FAF (point where you need to start descending), one is flying the latter not the former…
Near MAPT above MDA, with +V you can guess where the runway sits vs aircraft path, I am not sure why one should not use that precious information on non-precision?
Ibra wrote:
+V is just there to help you, it’s useless near FAF
Please elaborate.
Airborne_Again wrote:
Please elaborate.
On non-precision, you don’t descend when you intercept +V at platform altitude, you descend after FAF (as given by your DME distance, navigation FIX or whatever definition it has on the plates), maybe very obvious when hand-flying but you gotta watch the autopilot if he is armed against +V
The difference could be tiny like 0.1nm or large 1nm, after the FAF you can catch +V from above with your hands if you wish (as long as you respect your min altitude for a given distance)
minima should be no lower than circling minima which is also the case for CAT A and B, but not CAT C or D.
Good catch. I’ll tell austro control.
Ibra wrote:
On non-precision, you don’t descend when you intercept +V at platform altitude, you descend after FAF (as given by your DME distance, navigation FIX or whatever definition it has on the plates), maybe very obvious when hand-flying but you gotta watch the autopilot if he is armed against +VThe difference could be tiny like 0.1nm or large 1nm, after the FAF you can catch +V from above with your hands if you wish (as long as you respect your min altitude for a given distance)
As Peter hinted at, you can use VNAV up to the FAF, which gives you a seamless descent past the FAF. When I tried the LOWG VOR 16C approach in the GTN650Xi simulator, it actually did that automatically!
You still have to use the “real NPA FAF” whereas VNAV takes you “overlay FAF in GPS database”, while difference is very tiny if FAF is defined as existing navigation FIX but maybe not if based on DME rather than GPS distance, the difference is still academic compared to where “+V FAP” sits…
I will try not to do that in France as every NDB has same name as DME in the database: I would not trust VNAV to AT at Annecy to fly NDB on GPS 
Ibra wrote:
You still have to use the “real NPA FAF” whereas VNAV takes you “overlay FAF in GPS database”, while difference is very tiny if FAF is defined as existing navigation FIX but maybe not if based on DME rather than GPS distance, the difference is still academic compared to where “+V FAP” sits…
The overlay FAF is designed to be identical to the original FAF. Why should there be a difference at all? Roundoff errors in the database?
I will try not to do that in France as every NDB has same name as DME in the database: I would not trust VNAV to AT at Annecy to fly NDB on GPS
There’s no DME AT at Annecy, but never mind… As I wrote, you get this automatically. You set up the approach to start at the IAF (Chambery VOR in this case), and the box will automatically give you a VNAV profile to the FAF which respects all stepdown fixes. You don’t have to enter the profile yourself. And even if you did, you would define the profile relative to the FAF in the navigator flight plan – and that point will be the NDB and not any DME with the same name. (As the approach has been loaded from the approach database.)
I would be more inclined to use VNAV in a difficult case like Annecy, as it would lower the chance that I screw something up.
In any case, even if the nav box is supposed to do it automatically, it is always the responsibility of the pilot to respect any minimum altitudes and step-down fixes. You don’t blindly follow a glide path pointer, do you?
Peter wrote:
According to many threads here, Avidyne IFD boxes also offer +V. What I don’t know is whether they offer it if SBAS is not available, but that isn’t so important because SBAS is practically always available in Europe. Somebody can also check on an IFD sim what LGST shows
As I understand it, Avidyne provides +V when not in SBAS service volume. This was available before the GTN series added the capability. RTCA DO 229Cadded the following note that allows it, so it may be included in any GPS system that was TSO certified using DO-229C or later.
Note: LNAV equipment may provide advisory vertical guidance. Advisory vertical
guidance is defined as supplemental guidance where the barometric altimeter
remains the pilot’s primary altitude reference. This advisory guidance should
use the vertical path and deviations defined in Section 2.2.4. This advisory
guidance may be provided even when SBAS corrections or integrity information
is not available. This advisory guidance cannot be used to descend below the
LNAV MDA or step-down altitudes.
Ibra wrote:
On non-precision, you don’t descend when you intercept +V at platform altitude, you descend after FAF
Ibra wrote:
On NPA, you could hit “+V FAP” (point where +V touches the platform altitude) few nm before FAF (point where you need to start descending), one is flying the latter not the former…
That’s not consistent with the Graz LOWG VOR Rwy 16C approach posted by @Snoopy. That descent needs to start 2300’ higher and 10.2nm further out than the FAF. Waiting for the FAF to start descent just wouldn’t work.
chflyer wrote:
That descent needs to start 2300’ higher and 10.2nm further out than the FAF. Waiting for the FAF to start descent just wouldn’t work.
CDFA only starts after FAF? before that it’s cruise (climb, descent, level), the suggested CDFA profile starts at D11.7-MAPT, you could always dive at VNE between IAF/IF and FAF, fly my platform and stabilize, configure (gear, flaps) before reducing power at FAF?
Same if you are kept high or vectored by ATC, you are still in cruise mode and not yet entitled to stable config & approach, it’s after FAF where you start the stable continuous descent…
Airborne_Again wrote:
You don’t have to enter the profile yourself. And even if you did, you would define the profile relative to the FAF in the navigator flight plan – and that point will be the NDB and not any DME with the same name. (As the approach has been loaded from the approach database.)
Got it, I misunderstood it as Direct-VNAV outside database !
