Here's an excerpt from the UAvionix AV-30-C Installation Manual pp. 11-12:
The AV-30-C is approved for primary Attitude, Slip and Direction of Flight. All other functionality is supplemental in nature and may not satisfy regulatory requirements for required instrumentation.
5.1 Mechanical Instrument Replacement Approval is granted to replace legacy mechanical instrumentation as follows: - Installation of the AV-30-C (Dedicated AI mode) as the primary source for attitude and slip. Installation replaces the existing stand-alone vacuum or electrically powered attitude indicator.
- Installation of the AV-30-C (Dedicated DG mode) as the primary source for direction-of-flight. Installation replaces the existing stand-alone vacuum or electrically powered non-slaved directional gyro indicator.
Note that when installed as a DG, a reversionary AI is available for display. This functionality is supplemental only and does not satisfy requirements for a backup or standby attitude, turn and slip, or turn coordinator.
5.2 Non-Required Instrument Addition Approval is granted to install the AV-30-C as a non-required instrument, augmenting existing required instrumentation. In this configuration, the AV-30-C must not replace an existing required instrument.
5.3 Vacuum System Removal The aircraft’s vacuum system typically may be removed under a field approval process (FAA form 337) if no other systems or equipment requires it. The AV-30-C installation approval does not address this alteration.
If you have a vacuum driven attitude indicator and directional gyro, then the AV-30-C could replace them both along with the slip indicator. However, you might not be able to replace the electric turn coordinator. Of course, the slip indicator is usually integrated into the electric turn coordinator so I read this caveat to mean that you can't replace the turn coordinator even if you don't have an autopilot.
You don't need the vacuum pump if you replace the vacuum driven instruments. Looks like it would be a good way to update your panel without going with two Garmin G5s. It's a nice display and a bit more familiar than the G5 PFD display, although I like the G5 HSI display. Each G5 has a 4-hour backup battery. The AV-30-C has a 2-hour backup battery.
Compatibility with a Garmin GPS such as the GNS 430W or GTN 650 is a concern. Section 8.2.5 of the installation manual describes the optional RS-232 GPS interface and section 14 describes the standard protocol functions that are available over the interface. For example, my G5 HSI displays not only the heading and compass card but also the distance to the next waypoint and ground speed, which are coming from the GTN 650. Although these standard functions are available over the RS-232 interface, there's no guarantee that Garmin has implemented them in a particular version of its software. AV-30-C owners with them connected to Garmin GPS units would have to weigh in here.
I've learned the hard way that when two different manufacturers are designing (or updating) avionics software, compatibility is not assured. If you have a Garmin GPS like the GNS 430W or GTN 650 (like I do), then you would be better off spending the extra money on the G5s to assure compatibility.
Another issue is that the AV-30-C is
not approved for IFR according to section 8.2.5 of the installation manual, whereas the G5s are.
I noticed that section 5.3 in the AV-30-C installation manual quoted above describes the removal of the vacuum system as requiring a field approval using a 337. That doesn't necessarily mean that the FSDO has to come out to inspect the installation but it might, depending on the FSDO. Most of them are really backed up and short-staffed, especially with COVID these days. It might take a while to get approval. Some FSDOs just tell the A&P to send the 337 to Oklahoma City unless it's a unique installation. We have several A&Ps on the forum who can weigh in on this.