Dual G5 anomaly

[jamesm]

I discovered an interesting anomaly while doing some instrument flight training the last couple of flights . When power up both ADI / HSI positions came up as an ADI.

I thought it was weird but dismissed it by going to Lower (HSI Position) and selecting HSI and thought nothing of it other than that was weird the flights were IFR  but in VMC conditions so no real threat.  Both G5 were  displaying as I expected.  So I had the annual last month or I working something dealing with avionics like update to the Nav database and I must had pulled circuit breaker. about week ago  started  back up on the instrument flight training. until today it happen again but I believe I caught it today, this time the battery symbol something like 40% . cycled ADI position G5  CB and the battery symbol went away. See if comes back tomorrow.

CB  for ADI G5 was pressed all way in but yet it still came up on battery not sure if it was a one off or something lurking for me at a later date. 

I suppose I should have caught the first time but maybe my rambling might help someone else.

James M '67C 

[OR75]

I am not sure what the issue or anomaly you are seeing 

but the G5 ADI is supposed to be connected to the main bus and start as an ADI 

the 2nd G5 (HSI) is supposed to be connected to the avionics bus and start as an HSI (unless it senses from the CAN bus that there is no ADI connected in which case it starts as an ADI)

[jamesm]

when both G5's come up in ADI is not correct configuration. I have rarely  ,if ever, have seen both G5's come up ADI. I am pretty sure that it's not a CAN bus or power bus issue since all the starts done over last many years the G5's come up in the correct configuration as expected.  Older model Mooney's Did not have a separate avionics bus breaker/Switch.  The point I was trying to make is even if circuit breaker pushed in can be deceiving  and  give indication that it's working when it's not and over looking the G5 and me overriding to get the lower G5 to go into HSI mode should have been first clue. I will have to see next I go flying.

[OR75]

both G5 coming up as ADI is correct IF you power the HSI G5 first 

When you have 2 G5s, the first to get power will go into ADI mode

[skykrawler]

When the master switch is turned on the avionics relay is energized to TURN OFF the avionics.  If there is any delay in that (avionics bus powers on for a moment) then the #2 G5 may boot into ADI mode.

The avionics switch actually powers off the avionics relay to supply power to the avionics.

You might try pulling the breaker to the #2 G5 and pushing it in after the master has been turned on and before the avionics power is on.   It should stay OFF until the avionics is turned on.

 

[Vance Harral]

51 minutes ago, skykrawler said:

When the master switch is turned on the avionics relay is energized to TURN OFF the avionics.

While this is a common implementation, it is not universally true.  Some aircraft with avionics master switches don't have a relay at all, much less one with "off is on" logic.  In particular, aircraft not originally equipped with an avionics master often get an aftermarket solution that's just a simple, high-current-capacity switch that connects an avionics bus to the main bus when turned on.  Our airplane has that setup, and I'm guessing it's likely the OP's 1967 M20C has the same, simple solution with no relay.

Further confusing things is that the original installation instructions for a dual G5 setup specified connecting both devices to main bus power, such that both powered on with the master switch.  It sounds like the OP's airplane is set up this way.  But a later revision to the installation manual specified that the ADI should be powered from the main bus and the HSI from the avionics bus.  Garmin never came right out and said it, but I suspect that at least one of the reasons for this change was to better control the boot order of the two devices.  As others have indicated, boot order matters.  A G5 configured to be "Device 1" in HSI mode expects to find a "Device 0" configured as an ADI on the CANBUS on power up.  If it doesn't, it will itself boot into ADI mode, leaving you with both G5s running in ADI mode.  I'm sure the boot sequence firmware has some sort of delay tolerance to account for two devices powering up at slightly different times, but I think it doesn't work that well.  I've flown a bunch of airplanes with dual G5s, some where both powered up on the master and others with only the ADI powering up on the master.  In the airplanes where both devices power up on the master, I've had several, occasional incidents of them both booting into ADI mode, but I've never seen that with the split master/avionics power up.  I no longer find "two ADIs at bootup" behavior interesting or concerning when it happens, I just manually change the 2nd device back to HSI mode like the OP did.

 

[jamesm]

I may have misspoken ... regarding both G5 coming up as ADI's in the last few flights about the same time when Nav DB was due. so last week I loaded Nav DB in to standby, since the Current Nav DB had not expired. I had to manually switched from Standby to active for Nav DB to this months Nav DB (GNC355 & GNX375) . Once I did that the last two flight it have come top G5 ADI lower G5 HSI like almost always does since 2017.  My original Post was weeks before for Nav DB expired and I believe it was power problem.  As for the Avionics master switch,  I reluctantly installed. one of person who installed my GFC500 Autopilot said I needed one.  So I called Garmin and asked me not having the installation manual for the GFC500, I said show me where it says I need an avionics master switch however they never sent me the documentation stating the autopilot's must have an  avionics master switch, but said Garmin phone support said  I need a avionics master switch. I didn't use a relay way too many points of failure. it's 35 amp Circuit breaker/switch for avionics master switch. 

It's odd to see my configuration when it powers up to see both G5's come up with ADI's displayed. I suppose there is many different was to configure them. But when almost always comes up with Upper G5 as ADI and lower G5 as HSI probably ~98% of the time or more.  I was curious to know if it was indication of what  troubles could lie ahead for me. Just don't want to happen in  IMC or check ride or some other poor timing. 

 

James