G5 External antenna

[PT20J]

The G5 has an internal GPS receiver which uses an external antenna (the antenna is external to the G5 but not the aircraft -- it is designed to mount on or under the glare shield). Instead of using the internal receiver, it can be wired to receive GPS information from a panel mounted GTN or GNS GPS. I'm trying to figure out if there is any need for installing the external antenna if I have a G3X (which also has an internal GPS receiver and has an antenna mounted outside the aircraft) and a GTN 650Xi where the G5 is only a standby instrument. I'm curious what others have done.

Skip

[David Lloyd]

Shop told me it was not needed if you have another GPS source (your 650Xi).  

[PT20J]

Yes, clearly it's not required if there is a panel mount GPS. I guess what I'm trying to figure out is if there is a use case for installing it. Perhaps a complete electrical failure in which case the G5 running on battery is all you have.

[carusoam]

Having a plan for all the failure modes possible....

Or just the worst case...

Or just the most common case...

Like... What happens if battery#1 decides to go TU... and all the lights go down on Broadway...

What does the G5 have to get you home on its own?

• battery
• gps
• antenna

Sounds pretty powerful...

I’ve only lost my electrical system once... on a VFR day... portable garmin GPS worked pretty well...

PP logic only, not a mechanic or CFI....

Best regards,

-a-

[Vance Harral]

We elected not to bother with an external GPS antenna installation when we recently had a G5 ADI installed, even though it's our primary ADI.  GPS data is fed to our G5 from an external source (GTN 650 in our case, but any WAAS GPS will do).

Our rationale was that the G5 does *not* become unusable if it loses GPS signal.  The availability of GPS data allows the G5 to perform exceptionally good drift correction, but without that data, it can still provide "pretty good" drift correction using air data (pitot/static) to drive the drift correction filter.

The shops we talked to about the installation all claimed it was very rare for them to install the GPS antenna and configure the G5 to use its internal GPS.  Not saying you should just do what everyone else is doing, but it seems most shops and customers are coming to the same conclusion we did.

[jamesm]

I went the expensive route.... when installing My G5 several years ago under something like rev1  of the G5 installation manual. I installed the Comant  2480-201 Com\GPS (non WAAS) antenna this was before the glare shield  GPS antenna was an option. the com antenna  is for my GNC255 nav/com. My rational was I didn't want to drill more holes in the fuselage  for  another com antenna and new  GPS  which would have also cost me money.  Though the cost would have been not as much and also in the reduction of  drag department and again probably not enough to justify the added cost but over many years possibly, which  got negated when I had to install the ADS-B antennas.

James '67C

Edited April 10, 2021 by jamesm

[Ragsf15e]

I have dual g5s connected to my gns430w.  First, I think the G5 only allows you to select one source at a time, meaning that you have to go back through the config menu to switch to internal antenna if it’s configured for external (doesn’t auto switch) which includes restarting it.  Second, it works just fine if the gps signal goes off.  I have turned off my gns several times and there’s no noticeable change.  Finally, I turned off the gns and rebooted the G5 in the config menu, changed it to internal gps and it immediately picked up a signal with no antenna.  I had accurate groundspeed and track.  
 

So I don’t think you need an antenna  to pick up gps, and even if you did, I don’t think you need one to make the G5 reliable.

[PT20J]

Thanks for everyone's comments.

After reading all of Garmin's terrible manuals again (Installation, Maintenance, AFMS, and Pilot's Guide) it appears that with no GPS signal (panel mount GPS failed, no external antenna on the G5) that the G5 goes into DR (Dead Reckoning) mode. However, I can find no description of exactly what that mode is or how it works. I don't see any great advantage to having an external antenna. In the unlikely event that the entire electrical system fails, I can keep upright with the G5 (which will still correct the AHRS with air data) and navigate with the iPad. Besides, the external antenna is $199 and doesn't even have the correct connector -- you have to buy a $95 adapter. So, it would be probably $500 installed. This whole project is pushing $80K.

Skip

[EricJ]

43 minutes ago, PT20J said:

Thanks for everyone's comments.

After reading all of Garmin's terrible manuals again (Installation, Maintenance, AFMS, and Pilot's Guide) it appears that with no GPS signal (panel mount GPS failed, no external antenna on the G5) that the G5 goes into DR (Dead Reckoning) mode. However, I can find no description of exactly what that mode is or how it works. I don't see any great advantage to having an external antenna. In the unlikely event that the entire electrical system fails, I can keep upright with the G5 (which will still correct the AHRS with air data) and navigate with the iPad. Besides, the external antenna is $199 and doesn't even have the correct connector -- you have to buy a $95 adapter. So, it would be probably $500 installed. This whole project is pushing $80K.

Skip

I'm not sure it'll revert to the antenna if the driving GPS fails, although one would think it should.   Also, I seem to recall when I looked at this before that there isn't really any significant requirement on the attached antenna if there is normally a GPS unit driving it.  In my install manual the requirements for the antenna are pretty basic.   When I was looking at this I was looking at just putting a generic GPS patch antenna on it and there didn't seem to be any barrier to doing that, especially if mounted on/under/in the vicinity of the glareshield.

 

[Ragsf15e]

3 hours ago, PT20J said:

Thanks for everyone's comments.

After reading all of Garmin's terrible manuals again (Installation, Maintenance, AFMS, and Pilot's Guide) it appears that with no GPS signal (panel mount GPS failed, no external antenna on the G5) that the G5 goes into DR (Dead Reckoning) mode. However, I can find no description of exactly what that mode is or how it works. I don't see any great advantage to having an external antenna. In the unlikely event that the entire electrical system fails, I can keep upright with the G5 (which will still correct the AHRS with air data) and navigate with the iPad. Besides, the external antenna is $199 and doesn't even have the correct connector -- you have to buy a $95 adapter. So, it would be probably $500 installed. This whole project is pushing $80K.

Skip

You know the one thing I wish I had in total electrical failure? I trust the battery on the G5s to keep me upright, I can navigate and probably shoot an approach with the ipad, but I can’t talk to atc at all. I’d like an “emer” avionics switch that jumps #2 nav/com directly to my battery. The Pa46t I fly essentially has this in case you need to shut down all the electrical, including the master.

[Mark89114]

My understanding is that the G5 requires a GPS source, whether it is the internal GPS, which has no antenna or a ship source.  I had a well known mooney shop install a G5 and they didn’t tie it into the ship GPS, which would have been expensive.  It was working but the actual avionics shop seemed surprised that it was working.  They installed a Garmin antenna which we velcroed to the dash, total cost $200.  

[Ragsf15e]

2 hours ago, Mark89114 said:

My understanding is that the G5 requires a GPS source, whether it is the internal GPS, which has no antenna or a ship source.  I had a well known mooney shop install a G5 and they didn’t tie it into the ship GPS, which would have been expensive.  It was working but the actual avionics shop seemed surprised that it was working.  They installed a Garmin antenna which we velcroed to the dash, total cost $200.  

It does require gps input (either internal or external) for normal operation, but it’s designed to continue to work after losing the signal in case of ship’s electrical failure.  Supposedly this mode is slightly degraded, but it still looks perfect.  But yes, under normal circumstances, a gps signal is required to keep it perfectly aligned.

[Mark89114]

You have to have an antenna per the installation manual.  Just because there is a GPS receiver inside the G5 box DOES NOT mean there is an antenna there.  Just because it works doesn't make it legal and/or safe.  That was my point, the original installer DID NOT install an antenna, it is REQUIRED.  Below are the references.  

 

1.6.1.4 GPS Aiding The G5 requires GPS for attitude aiding. It contains an internal GPS receiver that can be connected to an external antenna or optionally can use external GPS input if available.

3.4.1 GPS Antenna A GPS signal is required. The G5 can use an external GPS antenna or GPS data from one of the GPS navigators or GTX 3x5 listed in Section 5. 

 

[Ragsf15e]

8 hours ago, Mark89114 said:

You have to have an antenna per the installation manual.  Just because there is a GPS receiver inside the G5 box DOES NOT mean there is an antenna there.  Just because it works doesn't make it legal and/or safe.  That was my point, the original installer DID NOT install an antenna, it is REQUIRED.  Below are the references.  

 

1.6.1.4 GPS Aiding The G5 requires GPS for attitude aiding. It contains an internal GPS receiver that can be connected to an external antenna or optionally can use external GPS input if available.

3.4.1 GPS Antenna A GPS signal is required. The G5 can use an external GPS antenna or GPS data from one of the GPS navigators or GTX 3x5 listed in Section 5. 

 

Yeah, I don’t think anyone said you didn’t need an antenna.

[Raymond Ritter]

Does anyone have experience with installation cost for a single Garmin G5 AI?

[TCUDustoff]

I'm getting close to wrapping up my dual G5 install with a 430W.  Since the ADI is supposed to be on the "Battery Bus," what I did was split my Avionics Bus and put a diode in-between the two bars.  This is controlled with a dual position Avionics Master switch: UP is ON through the Relay while DOWN is ON just for the three position bus bar directly through the Battery.  My 430W GPS circuit breakers are on this bus as well as the G5 ATT. This accomplishes two things:

• On the ground, I can power up the GPS and enter my flight plan and get weather / clearance.
• In the air, if I have a generator failure or an avionics relay failure, I can quickly isolate and run the Attitude Indicator and 430W from the battery.

Note that, without the GAD, you can't control an autopilot nor feed ARINC data to the G5.  But, and I confirmed this with the local avionics shop, the GPS data is fed via RS-232 to the G5.  So, long story short, this will keep the G5 in fully functioning attitude indicator mode and have GPS navigation, and a radio, in an emergency.  

[PT20J]

This sounds like the GNS 430W would be powered any time the battery master is on. Does the 430W installation manual recommend this? I recall reading in some Garmin installation manual, and also hearing from my avionics shop, that the hazard in having the radios on during starting is not voltage spikes as generally thought, but low voltage “brownout” caused by the starter’s high current draw. Garmin claims that the power supplies for the primary instruments that need to be on during start are specifically designed for this.

The concern is plausible as modern avionics use switching power supplies and the current through some components will increase as voltage drops. It’s generally current that is the limiting factor with semiconductors.

Skip

 

[OR75]

5 hours ago, TCUDustoff said:

I'm getting close to wrapping up my dual G5 install with a 430W.  Since the ADI is supposed to be on the "Battery Bus," what I did was split my Avionics Bus and put a diode in-between the two bars.  This is controlled with a dual position Avionics Master switch: UP is ON through the Relay while DOWN is ON just for the three position bus bar directly through the Battery.  My 430W GPS circuit breakers are on this bus as well as the G5 ATT. This accomplishes two things:

• On the ground, I can power up the GPS and enter my flight plan and get weather / clearance.
• In the air, if I have a generator failure or an avionics relay failure, I can quickly isolate and run the Attitude Indicator and 430W from the battery.

Note that, without the GAD, you can't control an autopilot nor feed ARINC data to the G5.  But, and I confirmed this with the local avionics shop, the GPS data is fed via RS-232 to the G5.  So, long story short, this will keep the G5 in fully functioning attitude indicator mode and have GPS navigation, and a radio, in an emergency.  

Honestly, it sounds complicated for what you get 

the G5 has a backup battery . You can have an external antenna to have GPS position 

an iPad or iPhone is a cheap gps navigation backup … 

the only times I would want to get a clearance before starting an engine would be at major airports (class B ) where you may have to wait on the ground between clearance and clearance to taxi. I like getting the engine warm before taking off anyway. 
And if I lost the alternator , I would want to land . That’s what light signals are for. 

just my 2 cents , recognizing every operates differently 

[Ragsf15e]

5 hours ago, TCUDustoff said:

I'm getting close to wrapping up my dual G5 install with a 430W.  Since the ADI is supposed to be on the "Battery Bus," what I did was split my Avionics Bus and put a diode in-between the two bars.  This is controlled with a dual position Avionics Master switch: UP is ON through the Relay while DOWN is ON just for the three position bus bar directly through the Battery.  My 430W GPS circuit breakers are on this bus as well as the G5 ATT. This accomplishes two things:

• On the ground, I can power up the GPS and enter my flight plan and get weather / clearance.
• In the air, if I have a generator failure or an avionics relay failure, I can quickly isolate and run the Attitude Indicator and 430W from the battery.

Note that, without the GAD, you can't control an autopilot nor feed ARINC data to the G5.  But, and I confirmed this with the local avionics shop, the GPS data is fed via RS-232 to the G5.  So, long story short, this will keep the G5 in fully functioning attitude indicator mode and have GPS navigation, and a radio, in an emergency.  

I like the idea of it, but would prefer the ability to have a switch between a “conventional” avionics switch and an “emer” avionics switch that has your items on it.  Normal ops would be conventional, all avionics off during start like Skip mentioned.  In an emergency, I could have gps, radio, etc.  I agree with @OR75 that a radio isn’t required, and neither is a panel gps, but IFR, a radio sure would be nice if you’ve got a long ifr divert ahead of you.

Edited June 13, 2021 by Ragsf15e

[PT20J]

I did ask Garmin technical support about the G5 external antenna and GPS requirements for the AHRS. Their email didn't answer all my questions, but between it and reading some threads on BeechTalk where the Garmin guys are more active at answering questions, I learned the following:

The G5 uses GPS and pitot/static aiding for the AHRS as follows:

1. If the internal GPS is available, it favors that. There is an internal antenna, but that may not work well in all installations so the STC calls for a glareshield mounted antenna. Originally, it was possible to use an antenna mounted on the fuselage but that option was removed for improved lightning resistance (I'm certain this is the case for a G5/G3X combination; I'm less sure in a single or dual G5 installation).

2. If the internal GPS is not enabled, then an external GPS must be connected by RS-232 to the G5. Apparently, if both external and internal GPS are connected the G5 will favor the internal GPS over the external GPS. How it determines that a source has become invalid  and decides to use the other was not described.

3. If no GPS is available, the G5 will use pitot/static sources for AHRS aiding.

4. If no GPS or pitot static is available, Garmin claimed in one thread that the G5 AHRS would be accurate enough to fly by for up to two hours.

Skip

 

[201Mooniac]

1 hour ago, PT20J said:

I did ask Garmin technical support about the G5 external antenna and GPS requirements for the AHRS. Their email didn't answer all my questions, but between it and reading some threads on BeechTalk where the Garmin guys are more active at answering questions, I learned the following:

The G5 uses GPS and pitot/static aiding for the AHRS as follows:

1. If the internal GPS is available, it favors that. There is an internal antenna, but that may not work well in all installations so the STC calls for a glareshield mounted antenna. Originally, it was possible to use an antenna mounted on the fuselage but that option was removed for improved lightning resistance (I'm certain this is the case for a G5/G3X combination; I'm less sure in a single or dual G5 installation).

2. If the internal GPS is not enabled, then an external GPS must be connected by RS-232 to the G5. Apparently, if both external and internal GPS are connected the G5 will favor the internal GPS over the external GPS. How it determines that a source has become invalid  and decides to use the other was not described.

3. If no GPS is available, the G5 will use pitot/static sources for AHRS aiding.

4. If no GPS or pitot static is available, Garmin claimed in one thread that the G5 AHRS would be accurate enough to fly by for up to two hours.

Skip

 

Skip, what Steve from Garmin explained to me was that if both the internal GPS was enabled and the G5 is also connected to an external GPS via RS-232 that it will use the GPS metrics (like HDOP, VDOP, etc.) to decide which was providing the better fix and use that information for the aiding.

[PT20J]

22 minutes ago, 201Mooniac said:

Skip, what Steve from Garmin explained to me was that if both the internal GPS was enabled and the G5 is also connected to an external GPS via RS-232 that it will use the GPS metrics (like HDOP, VDOP, etc.) to decide which was providing the better fix and use that information for the aiding.

Well, that would make sense. I do not understand why they don't publish some tech notes that explain how it works and what some of the tradeoffs are for various installation options. Maybe they sell enough stuff that they don't feel the need. Maybe they are arrogant and think pilots are too dumb to understand it.

[201Mooniac]

1 minute ago, PT20J said:

Well, that would make sense. I do not understand why they don't publish some tech notes that explain how it works and what some of the tradeoffs are for various installation options. Maybe they sell enough stuff that they don't feel the need. Maybe they are arrogant and think pilots are too dumb to understand it.

I also wish they published much more technical information.  I've found that most avionics installers don't really understand the technical details of how this new equipment works and without even having installation docs available that leaves those of us who really would like to understand trying to piece together bits of information.

[EricJ]

So it sounds like the best thing to do is to connect a glareshield antenna and enable the internal GPS.   Even if the glareshield antenna fails, if the RS-232-connected GPS is still providing data it will revert to that.   If that also fails, it'll revert to pitot/static.   I think if the internal GPS is not specifically enabled in configuration it'll ignore it?   This is still a little confusing...no surprise there.

Anyway, all of these recent discussions are making me glad I have a G5 rather than a GI-275, and if/when I go to replace my vacuum AI it'll likely be a G5.

 

[OR75]

I wonder if the GPS position information is transmitted between 2 G5s connected by a can bus ( in case only 1 G5 is connected to an antenna and rs232 signal is lost )