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GPS Hold

Postby dzk2000 » Sun Jun 23, 2013 2:37 am

I was making a practice gps approach to KSSQ rwy 14. At MDA I hit the Missed button and on climbout I changed to Direct ALEEN , the IAF for another approach. I then noticed an option in the menu called GPS Hold, or something like that. I haven't ever noticed that option before in the 1.5 years I've been flying the horizon. I pushed the button, thinking I would like to see it do a hold at ALEEN, I was VFR in VMC with no pressing destination to get to. My RV8 immediately made about a 90 degree left turn to the South, and the display showed GPS-Hold in the annunciator section in the upper left corner. Not wanting to go South and not knowing how to set up the hold-thing, I clicked through the menu to disengage the hold, and could not find anywhere to get out of this hold operation which was taking me to the South pole, apparantly. After about 5 minutes of searching the menu options in both PFD and Map mode, I finally disengaged the Trutrak VSGV autopilot and reengaged it to its own heading and altitude mode and flew it toward home. I finally was able to get the Horizon out of the hold mode by switching the nav source to NAV1 and then back to GPS2. I searched the pdf manual and there is no documentation on GPS Hold. What the heck is it? How do you set it up? How do you get back out of it?
dzk2000
 
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Joined: Sun Jun 23, 2013 2:06 am

Re: GPS Hold

Postby GRT_Jeff » Tue Jun 25, 2013 9:00 pm

The GPS SEQ HOLD function is called OBS mode on some GPS units. Flight plan sequencing is suspended, and the course knob allows you to change the inbound/outbound course through the active waypoint, similar to a VOR. The altered course is maintained until you return to GPS SEQ AUTO and sequence to the next waypoint. For the final waypoint, or a Direct-To, the course will be maintained until the waypoint changes.

When you activated the HOLD mode, it should have started with the course established by the direct-to. I am not sure why it started flying south. With the TruTrak VSGV in GPSS or EXT L/S mode, you shouldn't have noticed anything unless you changed the course with the course knob. We recently found a problem with the course data in the "Autopilot (Aviation)" serial output during a VOR or GPS HOLD, so that's a possible explanation if the ARINC autopilot source (GPSS or EXT L/S) wasn't selected on the TT.
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Re: GPS Hold

Postby dzk2000 » Wed Jun 26, 2013 11:06 pm

I appreciate the feedback, thank you. I do remember that I spent a lot of time running through all the menu options, round and round like a mouse in a maze running the same path looking for cheese, and I never saw the GPS SEQ AUTO option, otherwise I would have pressed it. Flying South would make sense if it was using OBS, because I had my heading bug on a southerly heading prior to making the approach. But you are saying it should have followed the Direct-To, which was West of me.

Funny you mentioned the bug with the serial / ARINC. My TT is hooked up simulataneously to both my Garmin SL60 GPS via serial, and to the GRT Horizon via ARINC. The TT defaults to using ARINC if it has valid data. The concept is that if my EFIS ever fails, I need to do nothing, the TT will automatically revert to the serial input from the SL60. So if the EFIS has a bug when switched to HOLD, and quits sending valid data over ARINC, the TT would have started using the SL60 serial input. When will the bug be fixed? I am on firmware 35g already.
dzk2000
 
Posts: 5
Joined: Sun Jun 23, 2013 2:06 am

Re: GPS Hold

Postby GRT_Jeff » Mon Jul 01, 2013 9:25 pm

The bug doesn't apply in your case. It only applies if the TT serial connection comes from the EFIS, and the serial output is set to the "Aviation" format. The ARINC output is not affected. The fix has already been tested and will be in all future updates. I am not sure on when the next updates will be published.
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Re: GPS Hold

Postby dzk2000 » Wed Aug 07, 2013 5:34 pm

Mystery Solved!

The GPS SEQ HOLD is found by pressing the right knob. I had been hunting for it by first pressing one of the soft keys, and those menus don't get you to the GPS SEQ modes. It is a really good thing to mention that there are two menu sets when dealing with people like me who are easily confused.

As for the plane going South when switching to HOLD, that is still a mystery if the Horizon was supposed to start with the Direct-To heading.
dzk2000
 
Posts: 5
Joined: Sun Jun 23, 2013 2:06 am

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