Why 2 GPS units?

I'm thinking hard about this myself for "part 2" of the Mooney's avionics upgrade.

We now have a GTN 750 as the #1 Nav/Com/GPS. We know we want a G3X Touch, G5 backup, and GFC 500... But there's still an old King KX165 #2 Nav/Com and I think it would stick out like a sore thumb in a panel full of Garmin stuff, not to mention the flaky screen that costs as much as an entire new radio to replace and the fact that it takes up too much room.

So, there's GPS, Nav, and Com. The second com is a definite need - I use that on every flight. But a second Nav seems like an emergency-use-only kind of item these days, and so does the second GPS when you've got one or two other large screens in the panel to use as MFDs, plus a third one in the form of an iPad...

If I had something with a bigger panel (310 or larger), I'd probably do what @James_Dean has in his Conquest: Dual GTN 750s + glass. Why yes, I have three monitors on my desk at work and I feel like that's not enough sometimes... I've even felt that way with six! But in the limited amount of space we have in the Mooney, and the limited amount of money in my wallet, IMO the 10" (left, PFD+MFD) + 7" (right, PFD or MFD) G3X displays make more sense, with the single GTN 750 in between.

With the amount of room we have in the main stack (about 10.5"), if we put the GMC 507 (GFC 500 mode controller) somewhere on the left hand side instead of in the stack, we have about 3.2" of vertical space available. That's plenty even for a GTN 650 (2.65"). However, A GNC 255 nav/com is 1.65", so we might even be able to move the transponder into the main center stack (it currently lives with the KX165 in the right-hand stack). The GTR 225 com is also 1.65" high.

Then, there's cost. The GTR 225 com is $2,095 (list). The GNC 255 is $4,495, and the GTN 650 is $11,995. The differences in cost will only be amplified by the differences in installation labor.

To me, that second GTN is overkill. I think the most likely failure mode for GPS is probably interference testing, which is going to take out all of the GPSs simultaneously... And it'll leave the GTN with the capability to shoot an ILS to get us down. Are we ever going to wish we had a second nav or a second GPS? :dunno:
 
flyingcheesehead said:
With the amount of room we have in the main stack (about 10.5"), if we put the GMC 507 (GFC 500 mode controller) somewhere on the left hand side instead of in the stack, we have about 3.2" of vertical space available. That's plenty even for a GTN 650 (2.65"). However, A GNC 255 nav/com is 1.65", so we might even be able to move the transponder into the main center stack (it currently lives with the KX165 in the right-hand stack). The GTR 225 com is also 1.65" high.
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I'm not quite following which goes where, but it sounds like you might be able to squeeze the GMC and a Trig TY97 or TX56 (33mm) into the stack.
 
asicer said:
I'm not quite following which goes where, but it sounds like you might be able to squeeze the GMC and a Trig TY97 or TX56 (33mm) into the stack.
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Right now, our center stack is, from top to bottom, annunciator panel, GMA 350c, GTN 750, KFC 150. Right-hand stack is KX165 and GTX 345, just above the yoke with a bunch of blank space above.

Our desire is to use that space above the right-seat yoke for a 7" G3X display, with a 10" on the left side. We'll need to get rid of at least one of the two things we have over on the right to fit that in.

I did get the stickers from Garmin at Oshkosh this year. Sometime soon I'll have to sit in the hangar and play pretend-panel. :)
 
I was just reading IFR magazine. The article was describing a "visual" approach in IMC by selecting the course to the runway and programming the VNAV feature of the GPS. With two 530s in my case, I could show the navigation page on the top 530 and the VNAV on the lower. I think later RNAV units could couple to this profile. Anyway it's another benefit of two units.
 
Jabe Luttrell said:
I fly a Cessna340. It has two Garmin 530Ws, a Garmin 345 Transponder, a Garmin audio panel and a Narco DME.
I like the two big gps screens. I select one for navigating and the other for traffic, weather, terrain, etc as necessary. I like the knobs. In turbulence touch screens are tough to use. For IFR the included VOR/LOC was a benefit when I installed the 530s but now a days the preflight briefing includes so many NOTAMs stating the VORs and ILSs are out of service that I basically am forced to rely on GPS. I also have a Foreflight iPad. It eliminates the 60 pounds of paper charts. The 530s do provide most of the data that the foreflight has except for the chartage and approach plates. Once you become proficient with the LPV and the LNAV/VNAV etc approaches you wouldn't hesitate conducting any approach to minimums. That said, I always fly with two pilots, me and Otto or me and a buddy. Someone should always be flying the airplane accurately and someone else should be managing the flight - two different tasks. Otto is my three axis autopilot with altitude hold. It keeps me from busting altitude during cruise. It turns to a vector precisely without overshoot or wandering. It keeps me from chasing the needle on approach. It nails the glideslope or glidepath. I manage the flight and the communications. Don't fly IFR without two pilots. It's just too much work. From my young and stupid days I learned that approaches with one NAVCOM and an ADF was possible but made for really wet underarms. Even then I used a wing leveler.
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Oh yeah, concur, single pilot IFR without an autopilot is hard work when in the clag; even in our 172, I'm grateful for our STEC AP that can track a GPS or VOR course. No altitude hold, but in a 172, things happen slow, so not an issue. I know guys flew plenty of single pilot IFR without an AP, but I'd want to be doing that a LOT, like flying professionally, before being cavalier about it. I'm OK with handling a AP failure in route, just up my game, my focus. But if I anticipated a long flight in the clouds, and knew the AP was broke before the flight, I'd probably cancel, or re-think altitudes and routes.
 
Jabe Luttrell said:
I was just reading IFR magazine. The article was describing a "visual" approach in IMC by selecting the course to the runway and programming the VNAV feature of the GPS. With two 530s in my case, I could show the navigation page on the top 530 and the VNAV on the lower. I think later RNAV units could couple to this profile. Anyway it's another benefit of two units.
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Or of the GTN series, which will calculate a guided visual approach to any runway, provided the software is recent enough (within the last couple of years, feature was added in version 5.something I think). If you have a GTN without it, get your software updated, there's lots of other goodies in newer updates as well.
 
I like the 530/430 set up. I don't usually crossfire. I put the flight plan in the 530 and direct destination in the 430. The 430 is on the nav screen with one of the data fields set to VSR. This way if I get a crossing restriction, I put in the 530 and always know where I am VSR wise to destination.
 
flyingcheesehead said:
Or of the GTN series, which will calculate a guided visual approach to any runway, provided the software is recent enough (within the last couple of years, feature was added in version 5.something I think). If you have a GTN without it, get your software updated, there's lots of other goodies in newer updates as well.
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Should be said that it comes with a huge warning that it doesn’t do obstacle calcs for that. Huge warning in the manual. Be cautious with it.
 
denverpilot said:
Should be said that it comes with a huge warning that it doesn’t do obstacle calcs for that. Huge warning in the manual. Be cautious with it.
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It is most definitely for visual approaches only. I think all it's doing is calculating a 3-degree glidepath along the centerline of any particular runway. It says something about the 3 degrees when you enable it, and I don't think there's any way to change that.

Still, a useful feature, if you respect its limitations, and basically doing exactly what the previous post was doing to give guidance for a visual approach, but with a lot fewer steps.
 
The advisory vertical guidance modes are potentially dangerous, especially at night at an unfamiliar airport. Best to fly the approach or keep the PAPIs in sight at all times. Obstruction clearance is not necessarily guaranteed if following advisory vertical guidance, especially beyond the MDA for the relevant approach. At many airports, including ours, PAPIs are not a standard angle, and may not match the approach angle, to further add to confusion. The FAA is asking airports to align their PAPIs with the approach angle with the most recent recharting.
 
Salty, your question has been answered. If I were you and had the money, I would get 2 ifr gps and dual nav coms with ils. Plus an autopilot. You say now that you will not fly in IMC regularly, but I suspect that when you get that ticket your attitude may change. Since I got mine in February I worry much less about ceilings and clouds. Ice and convective activity still worry me, but even thunderstorms, if isolated and not embedded are not that bad to deal with if you give them healthy respect and berth. My personal mins are +500 on mins and + 1 mile on vis. Not sure if that will ever change for me, we'll see.
 
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