GPS Approaches/Missed Approach

[RV6Bldr]

RNAV GPS RWY 30 KLRU.pdf

(608.4 KiB) Downloaded 658 times

Hi Katie,

I have the single screen HX System and am using a Garmin 430W as gps#1. When leaving my airport TA50, I put in KLRU direct in the Garmin 430. On climb out I turn on the GRT Auto Pilot, dial in 7500' push the button for Heading/Alt (heading is usually 030 degrees), while climbing out and before the a/p captures 7500', I set up the approach for rwy 30 gps approach for KLRU -Vectors. I then reset the GRT AP (enav, gpv, auto) for the approach to rwy 30 klru, the auto pilot will intercept the runway heading @ 45 degrees (@ this point I press the Execute button on the HX) and the HX will fly a perfect approach to the end of runway 30 @ KLRU! When reaching DA (4800/5000') I press the "Missed" button on the screen of the HX, and the OBS button on the 430 to sequence FIPAK, upon reaching FIPAK, the ap turns the RV6 left to Coses intersection. The 430 shows a holding pattern @ Coses with a tear drop entry, but the HX only shows triangle @ Coses intersection. If I let the a/p fly the plane, when I reach Coses intersection, the a/p will quit flying the plane! My question is "why doesn't the HX Efis show the holding pattern as depicted on the 430 screen"? What am I missing in the set up for the Missed Approach?

Thanks,
LLoyd

[Bobturner]

To follow a holding pattern the HX needs to be in gnav, not enav, mode. The info comes from the Garmin over the arinc line.

[Bobturner]

BTW, if you are on vectors, you should have the autopilot on HDG, and fly the vector given. With the autopilot on gps-lpv armed, it will automatically change over at final course intercept.
Make sure you hit obs on the garmin only after the missed approach point, when it has gone to suspend.

[GRT_Jeff]

External GPS units like the 430W do not send approach information to the EFIS. The EFIS only receives waypoint coordinates, without instructions on what to do at each one. The EFIS attempts to follow the desired track and cross track error from the GPS, but that's not always enough. To fly anything that requires more information, you have to use GNAV mode. GNAV mode lets the 430W tell the autopilot what to do. That means it's best to use GNAV mode before final and for the missed approach. For a GPS approach, if you start in GNAV mode, the EFIS will switch to ENAV mode during capture, and switch back to GNAV mode when you push MISSED.

[RV6Bldr]

Sorry for the delay, have had the RV6 down for the last 10/12 days getting the fiberglass parts ready for paint. Last Saturday I went back to KLRU and did the GPS 30 approach, same results. On the way back to TA50, I setup direct to ta50, got the gnav indication in the upper left corner of the efis and a little later I noticed the Execute button illuminated on the efis, so I pushed the execute button and noticed enav was now indicated in the upper left corner of the efis. Re entered everything for ta50 and got the same results. It seems that on my missed approach after the fipak intersection I pressed the execute button and that would take the efis out of gnav and put it into enav and the auto pilot would quit flying the plane at the hold intersection. This mornings flight I did not press the execute button between fipak int. and coses and it entered and flew the holding pattern followed by an approach. Works just like it should. Thanks to Bob Turner, GRT Jeff, and Carlos for your input. Now a Happy Camper!

[330drvr]

Jeff:

Thought I understood this, but now not so sure. Why would the EFIS leave GNAV on a GPS approach? I understand the change to ENAV for an ILS because of the raw data from the nav receiver but why on a GPS approach?

[GRT_Jeff]

We've just always favored our own autopilot calculations with the extra sensor data available. With ENAV mode, you get the benefit of AHRS data. I don't think anyone has analyzed the results, though.