Backup GPS for G3X system used for IFR approaches

I am planning a G3X system for my RV8 that will include a GNX375 as the primary IFR navigator. I realize if that fails I will be relying on the "VFR" navigator that is built into the G3X and the system will only show waypoints after the FAF. Does anyone on this thread know if adding a GPS20A to the system will provide a better IFR backup solution? IE access to the full instrument approach.

That only covers an internal failure. What if the gps system fails, e.g., deliberate jamming, or something else. Maybe I?m paranoid, because I have personally experienced a gtn650 presenting a big red X during an LPV approach (I never did find out the actual cause of the signal degradation). I carry around an SL30 nav/com, just so I can sleep at night. YMMV.

philfoshee said:

I am planning a G3X system for my RV8 that will include a GNX375 as the primary IFR navigator. I realize if that fails I will be relying on the "VFR" navigator that is built into the G3X and the system will only show waypoints after the FAF. Does anyone on this thread know if adding a GPS20A to the system will provide a better IFR backup solution? IE access to the full instrument approach.

Click to expand...

Hello Philip,

No, adding a GPS 20A doesn't turn the G3X GDU into an IFR navigator with the ability to load a full approach.

Could you explain what failure mode you are trying to cover?

It would be pretty unlikely to all of a sudden suffer a GNX 375 failure in the middle of an approach, but if it occurred, the G3X system will automatically revert to internal flight planning, with the approach intersections it received from the GNX 375 in the flight plan, using the WAAS GPS receiver internal to the PFD. You can push the NAV button on the GMC 507 to re-couple laterally to the flight plan and continue the approach without any vertical guidance, at least until you figure out your next move.

Thanks,
Steve

Steve,

Thanks for the reply. I suspect the reversion mode of the G3X is adequate for my needs in the remote chance of total failure of the GNX375.

Phil

STC upgrade for the GPS20A

Hi Steve,

Any plans to upgrade the GPS20A to STC it for IFR navigation so the G3x touch will be able to function like the G1000 and be able to input and perform GNSS approaches etc.

This would be the icing on the cake for this system.

Phil,
If you wanted the fixes before the FAF using your G3X, you could always just load them manually. They are in the data base, just not sinked with the approach. Can you legally use the G3X with manually loaded enroute fixes and file IFR with only that equipment? - nope, but you were talking about an unlikely failure mode, and what can I do to get out of it... If you need to be able to finish your vacation flying IFR with failed equipment, then you will need another IFR approved navigation source. If you just need to get the airplane on the ground to get it fixed, or into VFR conditions after a -375 failure, then that G3X is a pretty good resource.

Phil,

Agree with what Scott said.

The fact that every GDU 370/375/450/460/470 display has an excellent WAAS GPS receiver and full flight planning built-in is probably one of the reasons that so many G3X aircraft only have a single IFR navigator.

If your IFR navigator fails, you can fly autopilot coupled anywhere in the country with the built-in GPS. That is a great safety net.

While we are talking backup capability for an all GPS aircraft with G3X Touch and GNX 375 (like my aircraft), don't forget that the autopilot has 2 lateral modes (HDG/ROL) and 4 vertical modes (IAS/VS/ALT/PIT) that can be used to fly out of a no-GPS service area while talking to ATC, or just to get an ATC heading vector to an airport where you can land and wait it out.



So, if you lose GPS and all moving maps in the aircraft, stay in ALT hold, push in on the HDG/TRK knob to sync heading to current heading, and push the HDG button to re-engage the autopilot in HDG/ALT mode to give you a chance to deal with the loss of quite a bit of situational awareness and execute plan B.

Thanks,
Steve

Ian Coates said:

Hi Steve,

Any plans to upgrade the GPS20A to STC it for IFR navigation so the G3x touch will be able to function like the G1000 and be able to input and perform GNSS approaches etc.

This would be the icing on the cake for this system.

Click to expand...

Hello Ian,

Every G3X and G3X Touch display contains an excellent non-certified WAAS GPS receiver, but that is only the first small step in achieving performance and functional parity with a certified IFR navigator like the GTN 6XX/7XX (or G1000).

While the GPS 20A performs at a level consistent with a TSO-C145 WAAS navigation sensor, there is a large gap between just having this type of sensor and having a full-blown TSO-C146 standalone IFR navigator.

The two TSOs listed below specify the required performance and functions of a certified WAAS GPS navigation sensor (TSO-C145) and a complete stand-alone IFR navigator capable of being used for all phases of IFR operation including enroute, terminal, and approach (TSO-C146).


While the Airman's Information Manual may not be regulation (any you may not live in the U.S.), it is the FAA's guidance on using GPS for IFR operations.


It further specifies what is required to use GPS as the sole source of navigation (even enroute) if you are not using a WAAS corrected TSO-C146() navigator like the GTN.


Many reading this will quickly say "yes, but we fly EAB aircraft, so we don't need TSO'd equipment. We only have to meet the performance requirements of the TSO'd equipment."

While this may be true, meeting the performance requirements for IFR operations to safely fly down to minimums (sometimes 200 ft) in the clouds on an LPV approach is a tall order.

DO-229 specifies the Minimum Operational Performance Standards (MOPS) for TSO-C146 navigators like the GTN 6XX/7XX and GPS 175. It is over 500 pages and contains very strict requirements on just about everything imaginable associated with IFR navigation using a WAAS GPS navigation source.

The performance requirements for integrity monitoring and alerting to make sure a pilot does not continue toward the earth on a precision approach when the integrity of the 3D navigation solution is not assured are particularly stringent.

We take IFR operation very seriously, and feel that the G3X/G3X Touch integration with Garmin IFR navigators provides the best of both worlds for EAB aircraft. The affordability of a non-certified EFIS system with the design assurance, performance, and safety of a rule compliant certified IFR navigator.


Thanks,
Steve

Hi Steve,

Thanks for the explanation of the differences between 145 and 146 standards but my question really relates to the upgrade of the GPS20A so that it is comparable to a GIA63W within the G1000 suite, a 146 standard receiver to fully integrate the G3x touch system without a stand alone navigator.

Regards Ian

+1 on having the SL30.

It's a great complement to an IFR GPS as they each backup the other.