Garmin GTN 650xi vs GNX 375

Posted On August 18, 2020

The avionics are one of the more costly parts of a kit airplane build. It is easy to spec out an equipment list that totals more than the cost of the airplane itself. One costly option I discovered is deciding to equip your plane for IFR flight.

For a new plane being built today, a GPS IFR navigator is the only sensible choice. There are a few options on the market, but since I’m using Garmin avionics almost exclusively, my choices were either the GNX 375 or a GTN 650xi. They are not exactly equivalent devices, but both are the starting point for equipping an airplane for IFR.

A little background on me: I already have an instrument rating, and I prefer to fly on IFR flight plans for any kind of point A to point B trips. So, having a legal GPS IFR navigator with LPV approach capability was my first priority. Both the 375 and 650xi fulfill this need. In the end, I decided to spend a little more to get the 650xi, here are my reasons why.

Bigger Screen

The screen on the GNX 375 is pretty darn small. The unit is only 2″ high with a 4.8″ (diagonal) screen of 732×240 pixels, so you don’t see very much of a map nor flight plan. The GTN 650xi is only a little taller at 2.65″, and diagonally the screen is about the same at 4.9″, but it is taller and packs in more pixels: 834 x 370, or about 75% more pixels.

I think the bigger screen is a benefit particularly when practicing IFR flight. When I was going through my instrument training, or even today when I go out for currency flights, it’s not unusual for me to shoot 3 or more approaches back-to-back, and practice related maneuvers like holds and procedure turns. That means a lot of interaction with the GPS. Having a bigger screen to see the information and punch in selections on the touch screen makes a lot of sense.

Garmin makes an even bigger-screened GTN 750xi. It has a 6.9″ screen, but it is taller than it is wide. The cost for those extra 2″ is $5,500 and adds no other functionality. That’s a lot of money for just 2 inches!

Nav Receiver

The GTN 650xi includes both a Comm and Nav receiver, allowing a second navigation and approach means (VOR, ILS). Even though I think GPS will eventually fully replace VHF navigation, it’s probably not going away in the next 10 years at least. ILS approaches can still be found at any larger (class B, class C) airport, and at many smaller regional airports, like my class D home field: KASH in Nashua, NH. Bigger planes use higher-precision equipment to fly ILS approaches all the way down to the ground and land themselves too.

Although the GNX 375 will let you load ILS approaches (as will the G3X), it’s only legal to do so for monitoring under VFR conditions. And you might not be able to fly a published missed approach if it includes flying a particular radial to/from a nearby VOR station.

Because of the built-in Nav receiver, the GTN 650xi can seamlessly switch between GPS and Nav receivers during an approach. At one point I considered having a GNX 375 + GNC 255A, but then I would have to manually dial-in and switch both the nav source and nav frequencies during an approach. The GTN 650xi does this automatically.

Resale Value

The GTN 650xi (and larger-screened GTN 750xi) are Garmin’s flagship IFR navigators, and will therefore be more attractive equipment to a potential buyer, if I ever decide to sell my plane or just the GPS. The previous generations of Garmin navigators have always held onto their value and have lasted a long time. The GNS 430/530, introduced in the late 1990’s, are still common equipment today.

The GNX 375 ($8,000) and its two siblings are advertised as value-oriented products. The two siblings either drop the transponder (GPS 175) or swap it for a Comm radio (GNC 355) at attractive price points: $5,000 or $7,000, respectively. However, Garmin’s product announcement points out that this GPS 175 series was designed to replace older units like the GPS 150/155 and KLN 89/90/94 series, so it seems low-cost retrofits are really the target market, not new builds.

When I look at the low-cost segment of avionics, they seem to have shorter life spans, and lose their value more quickly. Indeed, Aircraft Spruce is already selling the GNX 375 for $6,695, which is 16% below the list price after just 1 year. There are similar discounts on the GPS 175 and GNC 355. To me, this trend seems similar to the many portable GPS devices on the market (Garmin’s Aera line, for example), which don’t seem to last very long. Time will tell how the GNX 375 holds up on the secondary market, but I expect the GTN 650xi will hold up better.

Long Product Support

The GTN 650xi and its bigger brother, the GTN 750xi, are Garmin’s latest tech, introduced earlier this year. It will likely enjoy a long support cycle, at least 20 years if you use the GNS 430 series as a yardstick. It will be used broadly in both new planes and retrofits. Most other Sling builders I see are choosing the GTN 650/650xi for their planes, and I imagine this is true for other experimentals as well.

Garmin very prominently boasts on the product page that the GTN 650xi/750xi feature dual-core processors which boost the graphical display capabilities compared to the previous-gen GTN 650. There’s no mention of what’s under the hood on the GNX 375, so I’m assuming it’s also previous-generation hardware.

Garmin will probably support the GNX 375 for a while too. The 375 and its siblings will likely make their way onto several retrofit panels, but I’m guessing you won’t find as many on new designs. As a result, I expect there will be a smaller installed user base for this product.

When you consider the larger user base that is likely with the GTN 650xi, it would receive priority for product support and future updates.

Backup Capability

I hesitate to say that having a Nav receiver adds “backup” capability in case GPS goes out – but I’m also adding it to my list, as it’s an argument I frequently hear. If for some reason GPS were not available, I’d still be able to navigate (albeit poorly) and perform some precision approaches using just VHF navaids.

I have yet to experience a GNSS outage in my 20 years of flying – or while driving, or sitting in my living room. In contrast, I’ve seen or experienced LOC, GS, or VOR outages at least a few times, so that’s why this argument doesn’t sway me much.

What’s the Price Difference?

The GTN 650xi by itself costs more than the GNX 375. But you also have to factor in the cost of a transponder and some other equipment differences. If you look at the GNX 375, you need to add a Comm or Comm/Nav receiver to reach some feature parity. The 650xi needs to be paired with a transponder. If Nav receiver functionality is truly not needed, Garmin sells the GTN 635xi for a $1,000 discount compared to the GTN 650xi.

Below are a few comparison cases, using Garmin’s list prices in USD. Street prices will be lower, and Garmin occasionally offers rebates. For example, the New Horizons rebate program that ran from Jun 1 – Aug 14 this year offered $500 back for the GTN 650xi when purchased with a G3X display. They haven’t yet offered rebates for the GNX 375, but street price discounts are pretty generous already.

In the comparisons below I’m using the GTX 45R as the transponder to pair with the GTN 635/650xi, since it offers ADS-B in/out like the GNX 375. Garmin also sells the GTX 35R, but it only offers ADS-B out, so no traffic or weather products to your dash. There are other transponder and ADS-B in options as well, but seem to quickly get messy with compatibility, so I’m ignoring those for this comparison.

In all cases, I’m assuming experimental versions of products (where applicable), integrated with a G3X Touch PFD. Prices for the certified versions are higher.

In cases A-B-C, the GNX 375-equipped panel doesn’t really change much in price, it just shifts around which boxes contain which functions, but without nav radio capability. Case D is the only apples-to-apples comparison, and even then there are functional differences.

Case A: No Nav Receiver, Minimal Panel Space Usage, Minimal Weight

In this baseline case, there is a large cost advantage to the GNX 375 setup. I chose to compare it with the cheaper version in the GTN line, the GTN 635xi (which lacks the nav receiver).

The GNX375 is paired with the inexpensive GTR 20 comm transceiver. With a remote-mounted GTR 20, you use the G3X display to control the comm functions. The GTR 20 also has a built-in 2-place intercom, eliminating the need for a separate audio panel. The GTN 635xi doesn’t have that, so a GMA 245R remote audio panel is needed.

IFR Navigator	GNX 375 $8,000	GTN 635xi $11,500
Comm Radio	GTR 20 $1,000	(built-in)
Transponder	(built-in)	GTX 45R $3,500
Audio Panel	(built-in to GTR 20)	GMA 245R $1,200
Total	$9,000	$16,200 (+7,200)

Case B: No Nav Receiver, Minimal Panel Space Usage, 4-Place Intercom

If a 4-seat intercom is needed, the GTR 20 won’t be sufficient. An external audio panel is needed to get audio to 4 places.

IFR Navigator	GNX 375 $8,000	GTN 635xi $11,500
Comm Radio	GTR 20 $1,000	(built-in)
Transponder	(built-in)	GTX 45R $3,500
Audio Panel	GMA 245R $1,200	GMA 245R $1,200
Total	$10,200	$16,200 (+6,000)

Case C: No Nav Receiver, Dedicated Controls for Comm Radio, 4-Place Intercom

The panel-mounted GTR 200 costs $125 extra. To get front-panel controls for the audio panel, a GMA 245 is needed which also adds $125 to the price compared to the remote-mounted model.

IFR Navigator	GNX 375 $8,000	GTN 635xi $11,500
Comm Radio	GTR 200 $1,200	(built-in)
Transponder	(built-in)	GTX 45R $3,500
Audio Panel	GMA 245 $1,325	GMA 245 $1,325
Total	$10,525	$16,325 (+5,800)

Case D: Nav receiver and 4-Place Intercom

This is the case where the GTN 650xi makes more sense. The price difference between the GTN 635xi and GTN 650xi is just $1,000, whereas to add Nav capability to the GNX 375-equipped panel, the only option is to add a GNC 255a Advanced Comm/Nav Radio. Garmin doesn’t offer an experimental-only version of the GNC 255a, so there’s a large price premium compared to the GTR 20, since you’re getting hardware that’s also suitable for type-certificated aircraft.

I added a GMA 245R to both configurations in this example. The price difference shrinks to $3,500 in this case. And, if you can factor in rebate savings for the GTN 650xi, the price difference is just $3,000, which is pretty small in airplane terms.

IFR Navigator	GNX 375 $8,000	GTN 650xi $12,500
Comm/Nav Radio	GNC 255a $4,500	(built-in)
Transponder	(built-in)	GTX 45R $3,500
Audio Panel	GMA 245R $1,200	GMA 245R $1,200
Total	$13,700	$17,200 (+3,500)

In Summary

In summary, I chose to go with a GTN 650xi, paired with a GTX 45R and GMA 245R to complement my G3X-equipped panel. For the extra $3,000-7,000 I’m spending (depending on how you look at it), I’m gaining:

• A bigger screen
• ILS and VOR navigation capability
• Better integration for IFR flight
• Better resale value and product support
• Probably better future-proofing