iFly GPS Forum

Hey all...

I'm having an interesting issue with a 740b and a TruTrak Digiflight IIVS autopilot.  The AP is connected to the iFly via the Adventure Pilot DB9-to-USB cable, connected to a DB9 connector that I made that connects back to the AP data wire and ground per the iFly manual.  There is a USB jumper between the factory cable and the iFly unit to to provide a 90° USB connection on the iFly side so the cable will fit in the Airgizmos dock I'm using.  The jumper was recommended to be by another iFly installer on the same aircraft type who has had no issues with using the exact same make/model cable.

The issue is that a couple of times in the air I have noticed the AP is working, but in HDG mode only, and will not go into NAV mode.  It's as if it cannot talk to the iFly unit, or doesn't "see" it anymore through the NMEA connection.  When this has happened I have gone into setup and confirmed the NMEA interface is active and set to extended data (which is how it has always been working).  The odd thing is, once I have shut down the unit (in this case, always on the ground after the flight), and restarted the iFly (for the next flight) the NMEA interface comes right up.  I have gotten into the habit of testing the AP before takeoff to ensure the NAV mode is tracking as a result of this.  Since I have started doing this it has always worked on the ground and in the air (just a couple of flights though).

As I see it there are two possibilities:

1) There is an intermittent connection issue with wiring.  I was pretty careful with this and used all high quality aviation wires and connectors and I do have some aviation wiring training, but it's certainly possible as I'm not a wiring expert by any meas, or...

2) There is a software bug in the iFly 740b that is causing the NMEA connection to be lost or stop talking to the AP.

I'm assuming that (1) is more likely, but before I start tearing into all the wiring, I wanted to ask if anybody else has had similar issues (or other AP weirdness) with an physical iFly unit connected to an AP.

Thanks!   

That's a good suggestion. You can check with TruTrak's documentation for what NMEA sentences they look for and disable the others. And of course make sure the baud rates match.

Could this behavior be related to the behavior described in this similar (but more recent) post?  http://www.iflygps.com/Support/Forum/...345/scope/posts (Edit:  copied wrong link here the first time.)

In that other post, it was determined that the undesired behavior occurred while on the ground, but the desired behavior occurred in flight.  Does your issue occur on the ground or in flight?  (Or both?)