Garmin IFR Navigators

There's no doubt that pilots love Garmin's IFR navigators. Most of the airplanes in my flying club's fleet have Garmin GNS 430s or GTN 650s. They're easy to use and bullet proof.

I've seen many of the newly completed E-ABs include a GTN 650 to fulfill the IFR navigation role. On occasion, some homebuilts sport the larger GTN 750 or an Avidyne IFR navigator of competing sizes and functionality. Even some of the more cost conscience panel are using available GNS 430/530 configurations.

I've given some thought to the role an IFR navigator would play in my Sling TSi panel. From an initial configuration perspective, an IFR navigator is not needed when the plane rolls off the production floor (that is, out of my garage). Certification and flight testing would involve no IFR use, and in fact, I wouldn't fly the plane IFR until it has at least 100 hours on it, maybe more.

So, what's my problem this time?

I find it interesting that the dimensions of the GTN 650, 635, & 625 cases are identical. Their weights are published as 7.0, 6.2, and 5.4 pounds respectively, so it appears the insides are different, as would be expected. I also find it interesting that each model is 8 tenths of a pound different from the next model regardless of the additional radio technology.

I bring this up because Sling builders have written about the need to modify the subpanel in order to fit the GTN 6xx and I wonder why Garmin made them all the same size. Perhaps Garmin's intention is to allow for slide-in upgrades between the 6 series and future offerings? Perhaps it is easier from a production/cost perspective to use the exact same form factor?

Whatever the reason, the large depth dimension of nearly 12 inches can be an inconvenience for some builders whose airplane designs typically accommodate smaller, modern avionics. We don't need a GPS navigator to fly IFR, but this where approach, departure, and en route systems are trending.