Vertical guidance RNAV (RNP) GTN750
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John Wayne KSNA, no issues w/ RNAV Y 20R, but w/ the RNAV Z (RNP) 20R I am not getting vertical guidance. Is this due to the aircraft / pilot not being authorized for RNP approaches? I tried it from JWARD, and from KLEVR, was at the correct alt for each of these initial apch fixes, but it just won't arm APR.
MSFS 2020, latest nav data from Navigraph (December update).
Really am enjoying flying the B58P all around SoCal including Vegas. Very nice.
Kirk
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Glad you're enjoying the aircraft so far. The very short answer is that this sounds like something to take up with the GPS developer.
The longer answer is that I think I have seen similar comments in the past. I think they were reference to the PMS50 GTN, and whether the user had Navigraph data installed or not may have also made a difference, but don't quote me. As I recall saying last time, this is just not a combination that I am very familiar with from my testing, since my instinct from real world flying is always to avoid selecting RNP approaches in light aircraft, for obvious reasons.
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Reasonable and understood. I did not mention that what occurs is that I cannot arm APR (whether using the button in the cockpit or the one on my hardware) for this RNP approach. But "AR" (approval required) is clear, most GA pilots are not trained/certified for RNP, and most GA aircraft are not certified for it.
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Thanks for this post as I was trying out RNAV approaches last night and although using a 430 I could get a glideslope on the KI 206 the flight director wasn't giving me any vertical guidance cues.
I'll try again tonight and I'm using the latest PMS GTN750 version so maybe the problem is between keyboard and chair.
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I happen to have a weird amount of GPS knowledge (probably a good thing cause I fly in real life). As far as I am aware, LPV (and/or "LNAV + V" on Garmin GPS units) use GPS altitude and not BARO altitude, where as RNP(AR) approaches actually use uncompensated BARO Altitude. Since the Century IV, and more specifically, the KAS 297B Altitude Selector do not have the capability to couple with the GTN 750/650 VNAV, vertical guidance will not be able to be provided when loading an RNP(AR). I trust TDS correctly implemented this due to the utilization of the Garmin Trainer Software, but PMS is not an accurate or technical simulation of the GPS.
More unnecessary info:
Technically for a GPS unit to load RNP(AR) approaches it would also require the ability to load Radial Fix (RF) legs. On Garmin Units Specifically this requires simulation of the latest TSO-C146c capabilities and not TSO-C146a capabilities, although these Technical Standard Order (TSO) designations actually have nothing to do with RNP(AR). It just happens that Garmin implemented RF leg capability to some units after TSO-C146b and I believe all their units since TSO-C146c. I believe Working Title simulates the G1000NXi and GNS 430/530 accurately as a Garmin TSO-C146a units omitting RNP(AR) approaches from being selected and the G3000 and G5000 as TSO-C146c which should be able to load RNP(AR) approaches (but I have little experience using the latter two in the sim). Since the TDS GPS units utilize the Garmin Training software, they simulate the latest TSO-C146c version and as such will be able to Load RNP(AR) simply because they can actually depict the RF Legs on the approach, but the units alone do not provide the requirements to fly the approach. Please let me know if you have any questions...More on Garmin GPS Limitations:
LPV requires WAAS Class 3, where as WAAS class 2 will only provide advisory Vertical Guidance indicated by "LNAV + V" on Garmin units. As far as I am aware all the Garmin GPS simulations in MSFS are WAAS Class 3 allowing you to fly any traditional "RNAV" or "RNP" approach with GPS Vertical Guidance in the sim (not RNP(AR) noting that many traditional RNAV approaches outside of USA are commonly designated as RNP). You will usually see "LNAV + V" on RNAV approaches where LPV is not available due to obstruction clearance requirements on the approach or there is a lack of SBAS equipment on the ground to provide accurate vertical precision. "LNAV + V" is to be treated as Advisory only and LNAV minimums are to be used, not LNAV/VNAV. -
I happen to have a weird amount of GPS knowledge (probably a good thing cause I fly in real life). As far as I am aware, LPV (and/or "LNAV + V" on Garmin GPS units) use GPS altitude and not BARO altitude, where as RNP(AR) approaches actually use uncompensated BARO Altitude. Since the Century IV, and more specifically, the KAS 297B Altitude Selector do not have the capability to couple with the GTN 750/650 VNAV, vertical guidance will not be able to be provided when loading an RNP(AR). I trust TDS correctly implemented this due to the utilization of the Garmin Trainer Software, but PMS is not an accurate or technical simulation of the GPS.
More unnecessary info:
Technically for a GPS unit to load RNP(AR) approaches it would also require the ability to load Radial Fix (RF) legs. On Garmin Units Specifically this requires simulation of the latest TSO-C146c capabilities and not TSO-C146a capabilities, although these Technical Standard Order (TSO) designations actually have nothing to do with RNP(AR). It just happens that Garmin implemented RF leg capability to some units after TSO-C146b and I believe all their units since TSO-C146c. I believe Working Title simulates the G1000NXi and GNS 430/530 accurately as a Garmin TSO-C146a units omitting RNP(AR) approaches from being selected and the G3000 and G5000 as TSO-C146c which should be able to load RNP(AR) approaches (but I have little experience using the latter two in the sim). Since the TDS GPS units utilize the Garmin Training software, they simulate the latest TSO-C146c version and as such will be able to Load RNP(AR) simply because they can actually depict the RF Legs on the approach, but the units alone do not provide the requirements to fly the approach. Please let me know if you have any questions...More on Garmin GPS Limitations:
LPV requires WAAS Class 3, where as WAAS class 2 will only provide advisory Vertical Guidance indicated by "LNAV + V" on Garmin units. As far as I am aware all the Garmin GPS simulations in MSFS are WAAS Class 3 allowing you to fly any traditional "RNAV" or "RNP" approach with GPS Vertical Guidance in the sim (not RNP(AR) noting that many traditional RNAV approaches outside of USA are commonly designated as RNP). You will usually see "LNAV + V" on RNAV approaches where LPV is not available due to obstruction clearance requirements on the approach or there is a lack of SBAS equipment on the ground to provide accurate vertical precision. "LNAV + V" is to be treated as Advisory only and LNAV minimums are to be used, not LNAV/VNAV.@SadBucket you really know your stuff, and thank you for that detailed reply, are you getting vertical guidance cues on the flight director when using an rnav approach?
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I happen to have a weird amount of GPS knowledge (probably a good thing cause I fly in real life). As far as I am aware, LPV (and/or "LNAV + V" on Garmin GPS units) use GPS altitude and not BARO altitude, where as RNP(AR) approaches actually use uncompensated BARO Altitude. Since the Century IV, and more specifically, the KAS 297B Altitude Selector do not have the capability to couple with the GTN 750/650 VNAV, vertical guidance will not be able to be provided when loading an RNP(AR). I trust TDS correctly implemented this due to the utilization of the Garmin Trainer Software, but PMS is not an accurate or technical simulation of the GPS.
More unnecessary info:
Technically for a GPS unit to load RNP(AR) approaches it would also require the ability to load Radial Fix (RF) legs. On Garmin Units Specifically this requires simulation of the latest TSO-C146c capabilities and not TSO-C146a capabilities, although these Technical Standard Order (TSO) designations actually have nothing to do with RNP(AR). It just happens that Garmin implemented RF leg capability to some units after TSO-C146b and I believe all their units since TSO-C146c. I believe Working Title simulates the G1000NXi and GNS 430/530 accurately as a Garmin TSO-C146a units omitting RNP(AR) approaches from being selected and the G3000 and G5000 as TSO-C146c which should be able to load RNP(AR) approaches (but I have little experience using the latter two in the sim). Since the TDS GPS units utilize the Garmin Training software, they simulate the latest TSO-C146c version and as such will be able to Load RNP(AR) simply because they can actually depict the RF Legs on the approach, but the units alone do not provide the requirements to fly the approach. Please let me know if you have any questions...More on Garmin GPS Limitations:
LPV requires WAAS Class 3, where as WAAS class 2 will only provide advisory Vertical Guidance indicated by "LNAV + V" on Garmin units. As far as I am aware all the Garmin GPS simulations in MSFS are WAAS Class 3 allowing you to fly any traditional "RNAV" or "RNP" approach with GPS Vertical Guidance in the sim (not RNP(AR) noting that many traditional RNAV approaches outside of USA are commonly designated as RNP). You will usually see "LNAV + V" on RNAV approaches where LPV is not available due to obstruction clearance requirements on the approach or there is a lack of SBAS equipment on the ground to provide accurate vertical precision. "LNAV + V" is to be treated as Advisory only and LNAV minimums are to be used, not LNAV/VNAV.@SadBucket I just wanted to take a moment to thank you for contributing your real world aviation knowledge to our forum. Although I know there are plenty of fellow real world pilots who frequent this forum, I often find that I am the one sharing my knowledge of real world flying, and worry that it's either not appreciated, or that my "nothing ever works that well in the real world" answers can sound evasive coming from the developer. Thank you for taking the time to do these writeups and sharing them with my users
