Course reversal with G1000 & KAP 140

[40flyer]

I have a 2005 non-WAAS version and trying to fly RNAV approaches with the G1000/KAP 140 combo. When I fly the outbound course to the IF/IAF the G1000 shows an apprpriate teardrop entry for the course reversal. With the A/P in nav mode it does not fly the teardrop but upon passing the IF outbound turns left all the way back to the Inbound course. I have tried approach loaded, approach activated, in NAV made and in APR mode and none of these scenarios flies the teardrop entry correctly. Do I have to do this entire procedure in HDG mode until intercepting the inbound course after the reversal?? Can’t figure this out. The approach I’m flying is the RNAV 28 at 6D6 with DOTIZ as IAF.

[blsewardjr]

With the Garmin 530 and KAP140 combo in my DA40, having the autopilot fly the course reversal requires both WAAS and GPSS. I have WAAS but not GPSS so must use the HDG mode.

[pietromarx]

I've had the non-WAAS / 140, the WAAS / 140, and the WAAS / GFC-700. Only the last flies the course reversal and/or holds in AP NAV mode, likely due to the lack of GPS-steering on the KAP-140 as Bernie says.

[40flyer]

Bernie/Pietro,
I have dual GPS which tracks flight plan RNAV legs no problem. But once I pass the IAF the A/P seems to be ignoring the course reversal. It’s as if the G1000 is not passing on that guidance.

[pietromarx]

Yes, that's right. The KAP-140 is a rate-controlled autopilot and can't handle things like DME arcs, course reversals, and holds. The G1000 with WAAS (and maybe without) does these things, but only when coupled with an autopilot that handles things like turn anticipation, etc. The GTX-700 autopilot will fly these things, but the KAP-140 can't.

[klang]

I see your point, however wonder why then the KAP in my DA42 is able to intercept and fly DME arcs? Have done this several times, never had a problem

[pietromarx]

OK - guessing here - but maybe the difference is WAAS in -42 and non-WAAS in the -40?

[blsewardjr]

Reviewing the difference between the Garmin 530 non-WAAS and the Garmin 530 WAAS, while both depict holds, only the WAAS version provides "active guidance" to the autopilot. I suspect the situation is the same for non-WAAS G1000's, i.e., they depict the holds, but do not provide "active guidance" to the KAP 140.

[Rich]

Keep in mind the autopilot is not a navigation device. It's a fairly simple control device. It is basically slaved to something that is a nav system. It's up to said nav system to tell George when he's off course and how far. It has nothing to do with rate vs. attitude.

In my plane in NAV mode, the FC takes orders from the HSI, which takes orders from the 530W. There is a similar command structure when the G1000 is involved.

[pietromarx]

My understanding is that the KAP-140 is connected via a pretty classic ARINC 429 interface to the various GPS'es. The software on the GPS is what drives the messages sent to the KAP-140, so I would guess that they added in roll or other functionality when they delivered WAAS that wasn't implemented in earlier versions.