LNAV+V in Australia

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Steve77
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LNAV+V in Australia

Post by Steve77 »

I am flying two brand new DA40NGs in Australia.

In Australia we don’t have SBAS (yet) and I understand the baro input is not “certified” so we can’t do LPV or LNAV/VNAV approaches. So I think the only GNSS approach I can do with vertical guidance is “LNAV+V”.

However i’ve noticed that when flying LNAV approaches, I am unable to get the vertical advisory “LNAV+V” Glide Path (GP) to activate (turn green) to automate the descent. After I press approach mode (APR) I can see GP preselected (in white) and GPS is active (green), but as I approach the FAF I never see the vertical deviation indicator or magenta diamond appear and the GP never engages. It just sits there preselected as I fly straight over the TOD point for the approach. I’ve noticed that when I initially select the approach, it only shows as “LVAV” and not “LNAV + V”. All databases are current.

The same approaches present as LNAV+V in Cirrus an GP engages as expected.

Does anyone know why I wouldn’t get LNAV+V approaches on a brand new DA40NG?


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chili4way
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Re: LNAV+V

Post by chili4way »

Two sources suggest that SBAS (WAAS) is required to generate path-oriented vertical guidance.

The first source is an FAA article from 2009 that states: "Some WAAS-enabled GPS units provide advisory vertical guidance in association with GPS approaches. The LNAV+V notation is simply the equipment manufacturer’s term for a GPS approach that includes an artificially created advisory glide path from the final approach fix to (the touchdown point on the runway."

The second source is an early version of the G1000 Pilot Guide for the Cessna 172 (Revision A, Feb 2007, 190-00498-02, page 2-9) that states: "NOTE: The Glidepath Indicator is only shown for aircraft with GIA 63W Integrated Avionics Units when WAAS is available."

This doesn't answer the question as to why Cirrus provides advisory vertical guidance (+V) that should require SBAS and Diamond does not (in Australia, where there is no SBAS yet). One possible explanation is that the Diamond aircraft has SBAS explicitly disabled. That would be evident by looking at the SBAS selection field of the AUX-GPS Status page on the airplane(s) MFD.

garmin-gps-status.png

If both the Cirrus and Diamond airplanes have SBAS enabled, about the same satellite reception, but still provide different +V availability for LNAV on the same approach, then perhaps Garmin technical support can provide the answer you're looking for.
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Re: LNAV+V

Post by Chris »

chili4way wrote: Thu Dec 08, 2022 5:11 pm Two sources suggest that SBAS (WAAS) is required to generate path-oriented vertical guidance.
Garmin's website states the same thing.
Garmin wrote:Most LNAV approaches are eligible for upgrade to LNAV+V. The criteria for being included in the database are:
  • It must be a GPS-approved approach.
  • There must be a non-zero vertical angle for the approach.
  • A valid geoid height for the runway must exist.
  • The approach does not contain LNAV/VNAV or LPV service levels.
Additionally, the unit must have a SBAS (WAAS, EGNOS, GAGAN or MSAS) signal of sufficient integrity. This means the GPS Status page must show “3D Diff Nav”.

If all these requirements are met, the Garmin navigator will automatically upgrade the approach from LNAV to LNAV+V.
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Re: LNAV+V

Post by Steve77 »

Very helpful thanks guys. I did notice my GPS status is “3D Nav” and not “3D Diff Nav”.

So this means it’s not possible to get any vertical guidance (LPV, LNAV/VNAV, or LNAV+V) on an RNAV/RNP approach in a Diamond in Australia? This is disappointing…

I even tried using VNAV during an RNAV approach and adjusting the FPA to match the approach (eg 3 degrees instead of the default 2.5 degrees) but it kept reverting to 1.7 degrees for some reason (Ie overruling what I set) and this would mean starting the descent too early and potentially breaching the minimum steps on way down. Any advice on how I can get VNAV to work during an RNAV approach?

Thanks
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Re: LNAV+V

Post by chili4way »

I'm puzzled how LNAV+V works on a Cirrus in Australia with no SBAS. It's not a Diamond-specific limitation.
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Re: LNAV+V

Post by Rich »

chili4way wrote: Fri Dec 09, 2022 2:23 pm I'm puzzled how LNAV+V works on a Cirrus in Australia with no SBAS. It's not a Diamond-specific limitation.
I often wonder about the efficacy of WAAS-based capability outside North America. The system requires a number of ground transmitter/receivers at known locations within a few hundred miles of you. Are there such stations in, say, Australia?

These ground stations transmit correction information to two ground-based stations, which then relay it to three WAAS satellites, which include the correction information sent out to the aircraft-based receivers. These satellites are geosynchronous, essentially placed above the Americas. It doesn't appear that these satellites' signals would be available to Australia.
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Re: LNAV+V

Post by chili4way »

More digging into this: Initial ("early Open Services") SBAS became available in Australia in September 2022. This suggests a software update might be required to process the L1 SBAS signal. "The Service Provider ID bits of the health and status word of Message Type 17 will be set to ‘8’ to indicate the navigation messages are provided by SouthPAN." Software version differences in the Garmin G1000 NXI system could explain the reported differences in LNAV+V availability between Cirrus and Diamond. The screenshot from the G1000 NXI Pilot Guide for the DA40NG (above) suggests only SBAS from WAAS, EGNOS, and MSAS are currently supported.

Article about the status of SPAN (Southern Positioning Augmentation Network) -- the regional SBAS solution. A technical explanation starts at 13:33. The part focusing on aviation starts at 33:54.
https://www.ga.gov.au/scientific-topics ... m/southpan

The following fact sheets (page 2) explains the characteristics of the "early Open Services."
https://www.ga.gov.au/__data/assets/pdf ... users-.pdf

The suggested next step would be to ask your local (Australian) Diamond distributor about the schedule for Diamond to support SPAN.
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Re: LNAV+V

Post by chili4way »

Consider retitling this thread as "LNAV+V in Australia (SBAS)"
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Re: LNAV+V

Post by Steve77 »

chili4way wrote: Thu Dec 08, 2022 5:11 pm This doesn't answer the question as to why Cirrus provides advisory vertical guidance (+V) that should require SBAS and Diamond does not (in Australia, where there is no SBAS yet). One possible explanation is that the Diamond aircraft has SBAS explicitly disabled. That would be evident by looking at the SBAS selection field of the AUX-GPS Status page on the airplane(s) MFD.

If both the Cirrus and Diamond airplanes have SBAS enabled, about the same satellite reception, but still provide different +V availability for LNAV on the same approach, then perhaps Garmin technical support can provide the answer you're looking for.
I have spoken to Garmin about this... They state "Just wondering if you have called Diamond up about their issue. Even without SBAS you should be able to do the LNAV+V without SBAS. This is something dictated by the manufacturer. We have many other GA aircraft here in Australia that can take the Advisory VNAV to the LNAV line of minima.. Im wondering why its not allowed in the DA's. We have loads of Cessnas 172's, 182's etc flying LNAV +V "

So now I am asking Diamond why they prevent +V with no SBAS if other manufacturers allow it.
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Re: LNAV+V

Post by Steve77 »

chili4way wrote: Fri Dec 09, 2022 2:23 pm I'm puzzled how LNAV+V works on a Cirrus in Australia with no SBAS. It's not a Diamond-specific limitation.
According to Garmin - it is an aircraft manufacturer decision as to whether they allow +V without SBAS. I also understand Cirrus has a "certified" baro pressure input (whereas the Diamond does not) and that is why Cirrus can do LNAV/VNAV in Australia. Garmin also suggested it may also be because of this certified baro input that the Cirrus allows LNAV+V without SBAS. But this is not clear yet.
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