flyingcheesehead
Taxi to Parking
If your immediate problem is a dying HSI, then dual GI 275's are a no brainer for your first step. Solves your HSI problem, significantly increases reliability by getting rid of your vaccum system, gives you redundant AI, and maximizes compatibility with current and future Garmin devices.
https://sarasotaavionics.com/avionics/gi-275-package
This! We have a very similar setup to Bill (Mooney, King autopilot/AI/HSI, etc) and this is exactly why we went with the GI 275. It can drive our existing King autopilot today, and it can also drive the GFC 500 should the King autopilot quit tomorrow. It allows for a staged upgrade approach very nicely.
Does the G3x not drive the king AP? I was under some impression that it did?
Nope. The G3X really only drives the GFC 500. Other autopilots need to keep another instrument (TC for S-TEC, AI for most other autopilots) to drive the autopilot.
The GI 275 can eliminate those extraneous instruments. Maybe at some point Garmin will update their hardware/software to allow the G3X Touch to communicate with the GI 275 and drive a legacy autopilot indirectly, similar to how the G500TXi can communicate with the G5 and drive the GFC 500 despite lacking the software to do it directly.
I really like those GI275’s and it might make sense in some cases, but for the cost of an AI and HSI and/or EIS, you could have a full blown G3X touch (or close to). Without a doubt, it makes sense to ditch the vacuum system, especially for more frequent IFR flying.
That's part of why we only did the single GI 275. We'd like to go full glass in the next few years and at that point we could use the GI 275 as a backup. If we were to get dual GI 275s now, one of them would likely be "wasted" later and we'd just end up selling it at a significant loss on the used market.
I gotta admit, I do kinda wish we'd done two of them... But if we had I'd probably be wishing I had more money.