530W / KAP-140 LPV approaches

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ahmebane
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530W / KAP-140 LPV approaches

Post by ahmebane »

Sorry if this is somewhat of a repeat - I've found relevant but not completely useful info on this topic.

I have a GNS530W with the KAP-140 autopilot. It flies fully coupled ILS approaches as expected. When trying to fly an LPV approach, the autopilot acts like it's not getting glideslope information. Even though its in APR mode, it maintains whatever the current set altitude is, there is no GS annunciation.

I've read about a menu item on the 530W to "enable autopilot outputs", but I have not been able to find that anywhere.

Anyone have this combo that is flying LPV approaches? Any pointers appreciated!
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blsewardjr
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Re: 530W / KAP-140 LPV approaches

Post by blsewardjr »

Holt- Your GNS530W has to be configured by an avionics tech to do this, but once done here's how it works.

From Page 120 of the latest GNS 530W Manual

Enabling Autopilot Outputs for the King
KAP140/KFC225
Autopilot outputs for the King KAP140/KFC225
autopilots are activated manually by the pilot after being
prompted during the approach procedure. After enabling
outputs, the 500W-series unit will provide guidance
information consistent with what the autopilot expects
(i.e., angular CDI scaling and glideslope capture for an
LPV or other vertically guided GPS approach).
Conditions for autopilot outputs
1. The 500W-series unit must be configured during
installation to interface with these autopilots and
using “Prompt” for GPS Select.
2. Guidance to the FAF is active as indicated by Approach
mode annunciation (LNAV, LNAV+V, L/VNAV, LP +V, or
LPV).
To enable autopilot outputs
1. Load and activate approach information as
usual.
2. When you are turned on course to the FAF (Track
and Desired Track are within 10°), a message
will prompt you to enable the autopilot outputs
before using your autopilot for an approach.
3. Press PROC. Highlight “Enable A/P APR Outputs?” with the large right knob, if necessary,
and press ENT.
4. Press the Approach button on the autopilot to
switch it to Approach mode. Your autopilot will
now use guidance from the 500W-series unit
for the approach.
Bernie Seward, IR, AGI
2003 DA40 N377DS
KCHO Charlottesville, VA
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Rich
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Re: 530W / KAP-140 LPV approaches

Post by Rich »

It's unclear whether my configuration conflicts with some part of the certification requirements, but it does not require that extra step and never has. This was true with the original KCS55A system as delivered and now with the Aspen. The 530W installation manual does make some reference to using the prompt option this but doesn't state it's required. I don't know if what I have violates some certification provision so I don't ask, as it behaves as one would desire. This is the GPS Select page from the Main System Config:
GNS 530W GPS Approach.jpg
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Re: 530W / KAP-140 LPV approaches

Post by Rich »

Note that there is also an Auto/Manual setting in the AUX Setup 1 page that is involved if the main system config is set to Auto. This is available to the pilot.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Re: 530W / KAP-140 LPV approaches

Post by ahmebane »

Update: The shop finally got to around it & I finally got the plane in the air to test the fix. The previous owner had upgraded to WAAS 530/430 units; however, the GPS select wire from the KAP 140 was going to the GPS Annunciate pin for the 530 and not the 530W - they're different. After correcting the wiring error the 530W drove the KAP140 as expected during an LPV approach. Yay!

My one question: why does the 530W have to be configured in the setup for prompting on the AP output? The choice is Prompt or Auto. Seems like Auto would be what one wants. I thought I might switch it to Auto & see how it behaves....

Thanks!
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Re: 530W / KAP-140 LPV approaches

Post by Lance Murray »

Auto works great.
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Re: 530W / KAP-140 LPV approaches

Post by ahmebane »

Final answer: yes, Auto works great, does NOT need to be configured for the prompt. Tried it out yesterday & it all works perfectly - 530W drives the KAP140 seamlessly in transition from heading/nav to approach mode.
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Re: 530W / KAP-140 LPV approaches

Post by blsewardjr »

Since my GNS530W/KAP140 is setup for PROMPT, I decided to do a little digging into why that was required for the KAP140 and the KFC225. Attached is a 2014 paper I found that explains the history of this issue, at least as it pertains to the KFC225. Basically, it has to do with the fact that the KFC225/KAP140 was designed to "kickout", i.e., switch to ROL when changing nav sources. The paper goes into great detail as to why that design feature impacts using GPS data for LPV approaches. It also explains why the KFC225 (and the KAP140 in my experience) doesn't fly GPS approaches any better than ILS approaches. Basically, as I understand it, the autopilot is not using GPS data directly but rather is tracking the HSI deviations just like it does for ILS approaches. The paper does not directly address what happens when AUTO is used instead of PROMPT but it may be related to certification of the GNS530W for use with the KFC225/KAP140 -- "Bear in mind that if the Garmin had not developed methods (GPS SELECT and PROMPT) to mitigate the dangers of the [KFC]225's kickouts, the FAA might not have approved the... 530W... to be connected to the [KFC]225."
Attachments
KFC 225 Internal GPSS overview 2014-11-01.pdf
(88.46 KiB) Downloaded 68 times
Bernie Seward, IR, AGI
2003 DA40 N377DS
KCHO Charlottesville, VA
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Re: 530W / KAP-140 LPV approaches

Post by Rich »

The KAP140 doesn’t kick out in this circumstance. For example, I’ve flown DME arc as part of an ILS approachvia GPS and switched to LOC to capture the ILS. Of course it has always been true that the HSI controls the AP, and I’m not really “changing sources”, just changing the GNS nav source sent to the HSI. This was true with the KCS55A and still true with the Aspen.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Re: 530W / KAP-140 LPV approaches

Post by blsewardjr »

I re-read the article several times to try to figure out how our 530W/KAP140 combo works. Apparently, the PROMPT vs. AUTO issue is due to programing choices Bendix King made when the KAP140 was developed in the non-WAAS, standalone, GPS days and the subsequent workarounds Garmin needed to make the combo work for a combined GPS/VOR unit that had WAAS GS guidance. The greatly simplified bottom line is that when the 530W switches from GPS to VLOC (e.g., when providing GPS guidance for the initial part of an ILS) and when it switches to providing GS information during an GPS RNAV approach (e.g, an LPV), the KAP140 responds by switching to ROL mode. (The explanation for why this occurs is very complicated, but it is more than simply changing nav sources.) The pilot then has to re-engage the AP in the APR mode. If the 530W does this automatically then the only indication to the pilot is the AP flashing that it is in ROL mode. To prompt the pilot to re-engage, for the KAP140 Garmin set it up so that the pilot manually switches the GPS to VLOC and manually enables the autopilot APR outputs. Then, as noted in the 530W manual, the pilot re-engages the AP in the APR mode. The theory appears to be that since the pilot manually initiates the actions that result in the AP switching to ROL, the pilot will see/remember to switch it to the APR mode. This is certainly what happens when I manually enable the autopilot APR outputs -- receive the message, hit enter on the 530W, AP switches to ROL, hit APR on the AP, GS arms. Are those of you who are using GPS guidance for your AP with the 530W set to automatic experiencing this switch to ROL during the initial part of the ILS or LPV approach?
Bernie Seward, IR, AGI
2003 DA40 N377DS
KCHO Charlottesville, VA
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