II VSGV Failover Sequence question

[PhantomPholly]

Hi Lucas,

I may have known this but forgotten. I have an IFR GPS (480) connected via ARINC, and also a hand-held (496) connected via Serial connection. The IFR unit transmits flight plan info to the 496 automatically. My autopilot is a DigiFlight II VSGV with the old magnetometer. My experience to date is that on some days I will temporarily lose GPS lock on the 480, but virtually never on the 496. This was true in my last airplane, too, with a 430/296 combo.

Question: If ONLY the IFR GPS loses lock, will the unit revert to GPS ground track using the 496 GPS info, or magnetic heading? I do know that under no circumstance would it automatically switch to the 496 flight plan - I would have to push the trk button and the AP would also have to think that there is no valid ARINC signal for that to happen.

I guess the real question here involves what the AP thinks about doing when it has a valid ARINC signal but the signal is saying, "I don't know where I am." Does it treat that as "No ARINC signal" or simply "GPS Lost." The difference to the question, I'm thinking, will determine whether or not the AP will "consider" information from the 496.

A parallel question would be, "what happens when the ARINC signal is restored?"

[TrutrakTech]

Hi Bill,

Ok. If you're tooling along on a flightplan from your 480 via ARINC and the signal goes south, be it from loss of GPS satellite or simply bad data coming out, the AP will leave GPSS/EXT LS mode. If your 496 is connected via the RS232 connection and is still feeding GPS ground track data, the AP will simply revert to GPS track mode and hold the current track.

Any hiccup in the ARINC data stream will cause the AP to leave GPSS/EXT LS mode. This is the safest route, rather than follow some erroneous directions the AP will simply continue on your current track.

If/when ARINC data is restored, you would have to push the MODE button again to re-enter GPSS/EXT LS mode.

I hope this helps clear it up. :)

[PhantomPholly]

Ok, so loss of GPS lock in your ARINC source is treated identically to power off - the AP goes and looks if it has a valid serial input source and, if so, holds current GPS course.

What happens if you are in serial GPS course mode and ARINC is restored? Continue GPS course, but use ARINC signal, or continue to use Serial?

This could be important, because sometimes I purposely do NOT cross-feed - and depending on when I hit the TRK button I may start following the 496 or the 480.

Too, what if I hit TRK (to follow the 496 flight plan) while it is consuming the serial stream and then subsequently the ARINC stream is restored? Does it continue to follow the 496 flight plan, or drop serial in favor of ARINC ground track?

I really wish we could program our failover modes. Even better would be if the screen had enough letters on it to indicate which source it is currently relying on (A/B/Mag). Well, some day... :D

[TrutrakTech]

Ok, I'll try to answer these in order. :D

If you're in TRK mode and ARINC signal is returned, it does nothing. It will continue in TRK mode. If no flightplan is being received over serial, then the flashing * will change to a flashing +.

If you're following the flightplan in your 496 via RS 232 and GPS Nav and ARINC is restored, it will continue to follow the flightplan on your 496. You would have to manually toggle back to TRK mode, then back to GPSS mode with the MODE button.

I hope this helps!

[PhantomPholly]

Ok, I'll try to answer these in order. :D

If you're in TRK mode and ARINC signal is returned, it does nothing. It will continue in TRK mode.

I'll be picky on this - track mode, using the serial-supplied GPS info or track mode, using the ARINC? Based on the second question's answer I'm thinking serial...

If you're following the flightplan in your 496 via RS 232 and GPS Nav and ARINC is restored, it will continue to follow the flightplan on your 496. You would have to manually toggle back to TRK mode, then back to GPSS mode with the MODE button.

VERY interesting! So, it is always "aware" that the serial signal is there but if you attempt to enter a flightplan mode it will pick ARINC, if available, but won't abandon serial if ARINC becomes available later.

Thanks Lucas!

[TrutrakTech]

I'll be picky on this - track mode, using the serial-supplied GPS info or track mode, using the ARINC? Based on the second question's answer I'm thinking serial...

We do not get any position data over the ARINC, strictly steering commands. Although many units will output position and navigation data, we only use the steering data.



VERY interesting! So, it is always "aware" that the serial signal is there but if you attempt to enter a flightplan mode it will pick ARINC, if available, but won't abandon serial if ARINC becomes available later.

Thanks Lucas!

Correct. If the DG in the top left is showing TRK, it's receiving serial data whether you're in GPSS or not.

[PhantomPholly]

We do not get any position data over the ARINC, strictly steering commands. Although many units will output position and navigation data, we only use the steering data.

Hrrm - well I didn't know that either. Does that mean that it won't even fly GPS heading mode if you have only ARINC connected?

Currently I only have ARINC connected (long story, I disconnected serial during troubleshooting under the theory that ARINC carried a superset of data). I hadn't actually tried pushing the track button without either a flight plan or direct to active.

That may explain the odd behavior I experienced coming home from Oshkosh.

[TrutrakTech]

Hrrm - well I didn't know that either. Does that mean that it won't even fly GPS heading mode if you have only ARINC connected?

Currently I only have ARINC connected (long story, I disconnected serial during troubleshooting under the theory that ARINC carried a superset of data). I hadn't actually tried pushing the track button without either a flight plan or direct to active.

That may explain the odd behavior I experienced coming home from Oshkosh.

Correct. If you have no serial connected and no flight plan active, you will get either the Mag heading mode or bank angle mode; depending on which unit you have.