Why 2 GPS units?

Salty

Salty

Touchdown! Greaser!
PoA Supporter
Joined
Dec 21, 2016
Messages
14,292
Location
FL
Display Name
Display name:
Salty
Why do so many people put up the dough for 2 in-panel GPS for IFR planes?

What capabilities / benefits do you get from having two when flying IFR?
 
Salty said:
Why do so many people put up the dough for 2 in-panel GPS for IFR planes?

What capabilities / benefits do you get from having two when flying IFR?
Click to expand...

Crossfill, and because stuff happens
 
James331 said:
Crossfill, and because stuff happens
Click to expand...
Can you elaborate on "crossfill"? I don't have my IR yet, and I have no GPS installed, so have have zero experience here.
 
Salty said:
Can you elaborate on "crossfill"? I don't have my IR yet, and I have no GPS installed, so have have zero experience here.
Click to expand...

Program on the one gps and the other gps automagically has all the info from the first. So you can keep the moving map up on one and scroll through the data pages on the other.
 
As @James331 and @EdFred says, and also many of these were installed before the advent of stuff like Foreflight on tablets. We had a club plane I few 13 years ago that had two 430's, it was nice. Now that I also have Foreflight, one suffices.
 
Crossfill
Basically what the others said, the top is a moving map with some data, the bottom you use like a FMS with your flight plan and waypoints and stuff.

Also dispatch, ForeFlight is cool and all, but you better not file as a /G if that’s your only GPS, and you sure wouldn’t want to shoot a approach with it. Thus if anything happens to one GPS nav/com and you only have one, well now you’re a VFR airplane, also if anything odd happens while in the soup it’s nice to have a cross reference as well as a second means of navigation you can switch to.
 
Bill Jennings said:
As @James331 and @EdFred says, and also many of these were installed before the advent of stuff like Foreflight on tablets. We had a club plane I few 13 years ago that had two 430's, it was nice. Now that I also have Foreflight, one suffices.
Click to expand...
That answered my next question, which was whether foreflight / GP makes the 2nd less needed.
 
James331 said:
Crossfill
Basically what the others said, the top is a moving map with some data, the bottom you use like a FMS with your flight plan and waypoints and stuff.

Also dispatch, ForeFlight is cool and all, but you better not file as a /G if that’s your only GPS, and you sure wouldn’t want to shoot a approach with it. Thus if anything happens to one GPS nav/com and you only have one, well now you’re a VFR airplane, also if anything odd happens while in the soup it’s nice to have a cross reference as well as a second means of navigation you can switch to.
Click to expand...
And that provides a good reason for having 2 anyway.
 
So my plan is to pop in a GNX-375, but that will require me to remove my 2nd NAV/COMM as there isn't room in my stack for both. My 2nd Nav/Comm is a giant MX-170C

There is room for both a GNX-375 & a GNC-355, which would give me redundant GPS & Nav/Comm, but will also cost me $7k more just for the hardware.

I have no plans on flying in actual IMC other than maybe to pop through innocuous clouds on an otherwise nice day. In fact, I don't even have plans to start my IR training quite yet so I'm debating the option of just popping for the GNX-375 and living with 1 GPS and 1 Nav/Comm for the time being. I don't really want to just pop in a nav/comm that will fit because even a used SL-30 will cost me a couple-three grand, and I really can't see spending more than 4 grand on a new garmin N/C. I'd rather put in something nice for a bit more, but it's a bit much for my budget right now.

I'm thinking I'm willing to risk having only one GPS and radio for awhile. 80% or more of my flying is blue sky VFR in familiar areas anyway.
 
I’d figure out your plans first.

Also no such animal as “just pop through a cloud” if you aren’t prepared to takeoff and fly IMC to mins, don’t play the IFR game.

I’d leave your panel be till you have a set plan, I’ve also seen some good deals on 430Ws from people chasing the Jones’s

What type of autopilot?

Single pilot IFR really should have a 2 axis AP with GPSS etc.
 
James331 said:
I’d figure out your plans first.

Also no such animal as “just pop through a cloud” if you aren’t prepared to takeoff and fly IMC to mins, don’t play the IFR game.

I’d leave your panel be till you have a set plan, I’ve also seen some good deals on 430Ws from people chasing the Jones’s

What type of autopilot?

Single pilot IFR really should have a 2 axis AP with GPSS etc.
Click to expand...
Of course I'd be prepared to fly to minimums. But I don't plan on planning any trip that REQUIRES it. I have no interest being in the clouds down low unless it's unavoidable, even when I do have my IR.

Autopilot is what I'm waiting on. Not doing anything until then. There aren't any choices for me yet, though probably my best bet will be the GFC-500. So yeah, I'm dreaming still.

You'll be hard pressed to talk me out of the GNX-375, it checks too many boxes. The 430 would require major changes to the panel, if I spend that kind of money I'm going to new tech.
 
James331 said:
I’d figure out your plans first.
Click to expand...

This line made me laugh. I'm trying to build a plan and you say I should figure out my plans first. ;)
 
- Dual receivers for backup. Also typically includes comm and traditional nav receivers.

- Two screens for more screen real estate.

- Cross fill.

If you already have another Nav/Com it’s less important, or if you’re worried about the second Nav/Com’s age or supportability.

Also for the screen real estate issue a Flightstream device (usually the 510 for GTN) pretty much alleviates that problem if you’re also flying with an iPad. Garmin Pilot can act as a (larger, brighter, better) display for the moving map using data from the GTN while you’re poking in some data menu. Not a certified device, etc... your mileage may vary.

The common setup you’ll often see for IFR is a GTN 750 and GTN 650 stacked. The 750 is the only unit that can display approach plates, so the plate will be up there and the moving map or other data on the lower 650.

Same effect can be done with Garmin Pilot on an iPad for the plate and a single 650 in the panel.

It’s all in how you want it displayed, what backup level you want, certified or not, etc.
 
That’s the touch screen version of my 530/430 stack.

After having flown GTN/GNS/G1000, for me I just don’t dig the GTN, I’m not as fast as I am, especially in chop, compared to the knobs of the GNS and G1000. I think the touch screen was a whiz bang idea thought up by someone with more computer time than flight time.

What I meant by figure things out, you don’t even have your IFR yet and you’re trying to build a IFR panel, perhaps get some sim time in and if you could use a desktop sim to play with different layouts. Lots of times it’s apparent (especially in experimentals) when a VFR pilot tries to make a IFR panel.

Personally I also like my iPad / plates on my lap. TONS of different ways of setting up “the office” thus my point of getting some IFR training before dumping truck loads of cash into a panel.
 
Because I can't afford 3...
In reality you should never have 2 of anything, because then you can't tell which one is wrong, you should always have an odd number. Although I guess technically my tablet or the old fashioned VOR receiver can break the tie between the 2 panel GPS units.

And if you only have one then you never know if it's wrong so you won't care.
 
Don’t see why I need an IFR before building an IFR panel. I’m not totally stupid, and I have a great resource where people can tell me what I should be thinking about. For example, I could start threads asking why you might want two gps units. Just as an example.
 
Two reasons...

1. Backup in case one fails. (Probably rare, but important if it happens.)
2. Sandboxing. That is, you can put contingency plans in #2 without farting up the flight plan in #1. Lots of uses: formulating plans around changing weather, putting in takeoff or destination alternates before you need them...These can be quickly cross filled into #1 if needed.

I wish I had two GPS boxes. :( But alas that is pretty expensive.
 
If you are building an IFR panel, you will probably want some ground-based NAV backup, certainly something capable of ILS approaches. For maximally capable IFR I would want to check the following boxes: at least one WAAS (TSO146) GPS, at least one VOR/LOC/ILS, and at least two COM distributed over two separate units. Plus an ADS-B panel solution with IN capability and the capacity to display on a panel unit and/or EFB. The #1 unit connected to the AP should have the GPS.

These days, there are lots of combos to get there. Just make sure everything can talk to each other, your (current or future) glass panel elements, and autopilot. And bring a pretty big checkbook. :eek:
 
chemgeek said:
If you are building an IFR panel, you will probably want some ground-based NAV backup, certainly something capable of ILS approaches. For maximally capable IFR I would want to check the following boxes: at least one WAAS (TSO146) GPS, at least one VOR/LOC/ILS, and at least two COM distributed over two separate units. Plus an ADS-B panel solution with IN capability and the capacity to display on a panel unit and/or EFB. The #1 unit connected to the AP should have the GPS.

These days, there are lots of combos to get there. Just make sure everything can talk to each other, your (current or future) glass panel elements, and autopilot. And bring a pretty big checkbook. :eek:
Click to expand...

The ADSB thing is IMO nice, but not needed.

Being able to switch the AP from nav 1 to nav 2 is a bigger deal.
 
James331 said:
After having flown GTN/GNS/G1000, for me I just don’t dig the GTN, I’m not as fast as I am, especially in chop, compared to the knobs of the GNS and G1000. I think the touch screen was a whiz bang idea thought up by someone with more computer time than flight time.
Click to expand...

Grab the knobs and spin them on a GTN. The UI is designed to be nearly identical as the GNS. Quite a few people don’t realize this.

It was a joke at the Garmin demo booth long ago. If someone had flown the GNS a long time they reached for a knob. If they hadn’t they poked at the screen as their first interaction with the GTN demo unit.

Give it a try. You’ll probably be surprised.
 
I have a 430 and I’m adding a GNX375. Adds more capability... I can have a moving map on the 430 and traffic on the 375 or use the 375 for LPVs if I need to. 430 has comms too
 
But wait, I thought you needed 4 gps's to get a 3 dimensional position?
 
My preferred setup for real IFR is at least one installed GPS (430, 530, 650, 750, etc.) and a ship powered, battery backup GPS (preferably panel mounted) such as a 396/496, etc. If you lose total ship power while IMC, the handheld will give you enough information save your bacon in an emergency. It may not be legal in normal circumstances, but in an emergency you do what you have to in order to survive.
 
Back to the original question, I dunno. I suspect it was just the most expensive way for the OEMs to offer dual GARMIN NAV/COMs and the GPS was just a bonus but was never the design goal for the panel. In my own panel I have a 2-screen Garmin EFIS, an SL30 and a GTN 650 plus a 2-axis autopilot. This setup has served me well flying IFR for the past 4-1/2 years.
 
Just my subjective opinion - two panel mounts is probably excessive, though not grossly so: We have a 530 and a Blue Tooth gateway (FS-210) - allows our 530 and ForeFlight to "talk" to each other. As in, exchange flight plan data, etc. I can have the approach active on the panel mount 530, and still have the "bigger" picture on my iPad. Or vice/versa. Two moving maps, with different scales if I want, or different displays altogether - looking at plates, airport data, etc.

Essentially, my iPad is my second GPS (I use a Dual GPS receiver with it). In practical terms, I use my iPad as "primary", until I'm in approach mode - it's just a faster, cleaner, more intuitive interface than the 530. Changes go in FF first, then to the 530, once I've done the necessaries. I back myself up on the 530, of course.

So if we already had a second panel mount, sure, I'd keep it. But I wouldn't buy a second one now - we already have an additional, independent nav/com, so we don't need a third radio. If the 530 failed on approach, we don't have a "legal" backup, of course, but we have ILS, a second nav/com, and I'd use FF to maintain a "lower stress" situational awareness.

I think in a higher end GA airplane, the marginal cost of a second panel mount might make sense - but we have a mid-70s 172; a second panel mount Garmin would be a significant percent of the airplane's value, and a 172 doesn't do anything in a hurry, so a GPS failure, even on approach, won't raise your blood pressure. In a higher performance airplane I could see buying a second.

Hope this helps. . .
 
One thing I will add, it’s very uncommon to see a working IFR plane that doesn’t have at least two navcomms, for overwater stuff you actually need two comms as I recall, thus might as well make them navcomms
 
James331 said:
One thing I will add, it’s very uncommon to see a working IFR plane that doesn’t have at least two navcomms, for overwater stuff you actually need two comms as I recall, thus might as well make them navcomms
Click to expand...

Why would you need a vhf nav flying overwater? It’s useless overwater unless you’re doing a coast in/out fix.

INS/IRS yes, GPS yes, dual comms yes..dual Navs? No.


Sent from my iPhone using Tapatalk Pro
 
Fracpilot said:
Why would you need a vhf nav flying overwater? It’s useless overwater unless you’re doing a coast in/out fix.

INS/IRS yes, GPS yes, dual comms yes..dual Navs? No.


Sent from my iPhone using Tapatalk Pro
Click to expand...

I was talking comms via the regs

Nav wise, if you’re putting in two comms, might as well make them nav comms eh?
 
Not these days. I really had to contemplate putting even 1 VHF nav in my plane during the avionics upgrade.

I have a GTN650 and a Garmin 225 for additional comm. I definitely believe in a backup comm. If I lose all electrical, I have the Aera660, GDL51, and 2 G5’s with enough battery endurance to get me anywhere and still have weather and METAR info. I also have the iPad too with AHRS and GPS info from the GDL51.

These are inexpensive backups priced well below the second VHF NAV with a ton more capabilities.


Sent from my iPhone using Tapatalk Pro
 
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.
 
You must log in or register to reply here.
Back
Top