KAP140 coupled approach question

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Rich
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Re: KAP140 coupled approach question

Post by Rich »

Over the years (including recent history) I've had to (and/or come to) revise my steps, given installation of a FS210 and Aspen. This is true even for enroute phases. The former since FF and my 530W now have a FP/approach synchronization capability. And upon the Aspen installation I needed to make an adjustment in handling the event of transitioning to Approach mode for RNAV approaches and incorporation of flying a coupled DME arc to ILS. I haven't had occasion to try the DME arc for a VOR approach yet. I wonder also whether I could pull off one of those complicated RNP RNAV approaches. KRDM does have such a thing.
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: KAP140 coupled approach question

Post by Rich »

So much for trying the RNP types. Foreflight has them available and you can load one into a flight plan but the GNS database doesn't have them, so no go. Not terribly surprising.

I've been looking for where this is documented, but my KAP140 will not capture GS from above. This isn't a bad thing for obvious reasons. But if I somehow start an approach at a position where I'm above the GS I find I have to manually (using CWS) fly it down to where I'm just a smidge below GS and then let it capture and fly from there.

I was recently watching a webinar linked to the American Bonanza Society where the presenter was focusing on behaviors of older autopilots. These are still in use, apparently, among this population of aircraft. Some of these really old autopilots require 20-40 seconds on the localizer before they'll capture GS. :shock:
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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nathanda40
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Re: KAP140 coupled approach question

Post by nathanda40 »

Rich wrote: Fri May 21, 2021 8:38 pm So much for trying the RNP types. Foreflight has them available and you can load one into a flight plan but the GNS database doesn't have them, so no go. Not terribly surprising.

I've been looking for where this is documented, but my KAP140 will not capture GS from above. This isn't a bad thing for obvious reasons. But if I somehow start an approach at a position where I'm above the GS I find I have to manually (using CWS) fly it down to where I'm just a smidge below GS and then let it capture and fly from there.

I was recently watching a webinar linked to the American Bonanza Society where the presenter was focusing on behaviors of older autopilots. These are still in use, apparently, among this population of aircraft. Some of these really old autopilots require 20-40 seconds on the localizer before they'll capture GS. :shock:
yeah i think ours has a similar issue (or maybe it's just how it's designed). yesterday it captured a localizer and glideslope perfectly and flew me down to near minimums without issue. other times, the gs won't arm. will have to take note if this only happens when i'm above the gs.

i suppose this makes some sense, as perhaps it only "trips" as the gs passes through the neutral area. so if you start above it you never end up near it, and it won't trigger
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Re: KAP140 coupled approach question

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nathanda40 wrote: Fri May 21, 2021 9:35 pm i suppose this makes some sense, as perhaps it only "trips" as the gs passes through the neutral area. so if you start above it you never end up near it, and it won't trigger
I never thought of it that way. I'll give this a try next chance I get to practice:
1. Be intentionally high when switching to approach.
2. Switch ALT to VS.
3. Set dive-bomb VS (1000 FPM?)
4. Power back to maybe 7-8 inches or as necessary to keep speed down.
5. See what happens :D
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: KAP140 coupled approach question

Post by blsewardjr »

Interestingly, according to the DA40 POH Supplement A13 "NOTE- Autopilot can capture glideslope from above or below the beam" (Page 9 - A13 -24 - 2005 edition).

The Cessna 182 POH puts it slightly differently - "The KAP 140 autopilot can lock on the glideslope from above or below. Capturing the glideslope from above is not recommended."

hat said, I've never gotten it to capture the GS when the HSI indicated I was above the GS, i.e. if I switched to the APR mode AFTER I had passed over the GS, the KAP 140 would not descend the aircraft automatically.
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Re: KAP140 coupled approach question

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blsewardjr wrote: Fri May 21, 2021 11:56 pm Interestingly, according to the DA40 POH Supplement A13 "NOTE- Autopilot can capture glideslope from above or below the beam" (Page 9 - A13 -24 - 2005 edition).

The Cessna 182 POH puts it slightly differently - "The KAP 140 autopilot can lock on the glideslope from above or below. Capturing the glideslope from above is not recommended."

hat said, I've never gotten it to capture the GS when the HSI indicated I was above the GS, i.e. if I switched to the APR mode AFTER I had passed over the GS, the KAP 140 would not descend the aircraft automatically.
I think Nathan may have supplied the clue. In order to capture the GS it has to essentially collide with it. As soon as I get some decent weather I'll test this hypothesis.

Capturing from above needs to be done carefully. You can't just nose down without reducing power, perhaps substantially. In the CWS scenario I mentioned, this is a critical part of the procedure.
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: KAP140 coupled approach question

Post by perossichi »

There was a question about putting the KAP 140 into ROL mode before intercepting the localizer. I have never done that and I do not understand what that achieves. When being vectored, you want to be in HDG mode with the segment of the approach you will intercept activated. When you get “maintain xxxx until established, cleared ILS...”, then you make sure you are on VLOC and hit APR on the KAP 140. Note controllers are required to vector you to with 30 degrees of the approach course. The KAP will intercept the course and arm the GS.

I have never tried nor seen the need to intercept the GS from above. Pro tip: you can intercept the GS at any point prior to the FAF and fly it. It is not necessary to dive down to GS intercept altitude before the FAF and intercept GS at the FAF. In particular, if the approach is steep, you can find it easier to fly a more stabilized approach by intercepting the GS before FAF. As long as you are between the IF and FAF with the localizer identified, you can capture and fly GS.

I suppose if you really wanted to intercept the GS from above, you could hand fly until you are flying GS and then put KAP 140 in APR mode which will work.
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Re: KAP140 coupled approach question

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perossichi wrote: Sun May 23, 2021 5:16 pm I have never tried nor seen the need to intercept the GS from above. Pro tip: you can intercept the GS at any point prior to the FAF and fly it. It is not necessary to dive down to GS intercept altitude before the FAF and intercept GS at the FAF. In particular, if the approach is steep, you can find it easier to fly a more stabilized approach by intercepting the GS before FAF. As long as you are between the IF and FAF with the localizer identified, you can capture and fly GS.

I suppose if you really wanted to intercept the GS from above, you could hand fly until you are flying GS and then put KAP 140 in APR mode which will work.
I have had, and have read of, cases where you wind up just a bit too high as you turn on to the approach. We're not talking full deflection. The merest smidge will do it. I hadn't thought before why it wouldn't grab the GS in these cases. My response has been to use CWS to manually get just a wee bit below GS (careful to keep my airspeed down) and then release CWS, whereupon it captures just fine. I figure to try the alternate switching from ALT to VS while in APPCH mode and see if it will capture by itself. This is an academic exercise if nothing else to better understand the AP behavior.

I've also found capturing ILS and WAAS requires slightly different button-pushing sequences.
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: KAP140 coupled approach question

Post by perossichi »

Ok, ATC procedures require that the approach intercept occur before the approach gate which starts one mile from the FAF. Given that a 3 degree approach is about 310 ft per mile, to vector you onto the approach course above the GS they have to leave you very high. Typically, I get vectored to an intercept at least 3 miles from the FAF. So to get vectored so that you are above GS at the time of intercept would require you to be very high.

The min altitudes for each approach segment are all below the GS.
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Re: KAP140 coupled approach question

Post by Rich »

Here's an example where ATC has no requirement to consider a glideslope and where they kept me too high: The RNAV RWY 10 here at S39 is an LP/LNAV approach. Technically it does not have a GS. So as long as I'm above the minimum altitude, they've fulfilled their obligation.

But in reality my GNS units (as with most modern UNITS) will turn it into an LP+V, giving me a glideslope to which it will couple just as it will with an ILS. I've had them do this on a practice approach at KBDN, also. That one is an actual LPV. I don't recall specifying the "LPV Approach" or just RNAV. I'm not sure it would have made a difference. I speculate that ATC assumes the lowest common capability (LNAV) for RNAV approaches.
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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