Dual nav radios no longer needed?

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John Myers

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John Myers
In the process of replacing a panel, I'm trying to find a reason to install a second nav radio in an aircraft that will have two WAAS units and one nav radio. I can see needing one nav as a backup to a GPS outage, but I can't come up with a reason to need a second one without resorting to contrived or implausible situations. Given the increasingly robust GPS constellation, you could even make an argument for zero nav radios, although I wouldn't take it that far.

The closest would be an approach like the LOC/DME into KASE, which has slightly lower minimums than the GPS approach, but the MAP for the GPS approach is much closer to the ALS, so I would probably still run that one anyways. I'm having a hard time definitively saying there are no others. It would be no fun to be surprised with an airport that I needed the second nav for and be unable to run the approach wanted. Does anyone know of one or have other thoughts?

Incidentally the panel will be G500 TXi w/EIS, GTN 750, GTR 225 (digital com, but they also make a GTR 255 that also has a nav radio, hence the question). Will usually have an iPad also.
 
Make sure you have 2 com radios, but with dual gps I think you’re good.

For instance I kept the dme in my plane while making upgrades, but I wouldn’t buy a new one...


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You mention having two WAAS units, but in your list, you only show one, the GTN 750.
 
I like both radios to have the same capabilities ideally, even on a ILS I like both up on the ILS and nav heads going for both just to see them doing the same thing, belt and suspenders I guess.

Now if it’s a VMC plane not really a issue though.
 
John Myers said:
G500 TXi has a GPS in it.
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Thanks. I didn’t realize that. I looked briefly at the description on Garmin’s web site, and didn’t see that the G500 TXi had internal GPS. Learn something new!!
 
James331 said:
I like both radios to have the same capabilities ideally, even on a ILS I like both up on the ILS and nav heads going for both just to see them doing the same thing, belt and suspenders I guess.

Now if it’s a VMC plane not really a issue though.
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It's a 340. One of the radios is a 750 and the other is a GTR, so they are much different units regardless. When would you use an ILS if you had an LPV approach? To my knowledge there are no airports left with both an ILS and no LPV approach, but I don't know how to definitively verify this.
 
Every once in a while you'll find an ILS with lower mins than an LPV. How often, I don't know.

What do ya know. found one on my second hit.

KBIV RWY 26
ILS gets you to 886
LPV gets you to 951
 
EdFred said:
Every once in a while you'll find an ILS with lower mins than an LPV. How often, I don't know.

What do ya know. found one on my second hit.

KBIV RWY 26
ILS gets you to 886
LPV gets you to 951
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Good point. No second nav needed for that one though.
 
Juliet Hotel said:
Is that a WAAS GPS that can shoot and approach?
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It is designed (I believe) as a backup, so I would assume so on both counts although I haven't read the manual.

But in any case, mostly concerned with needing the old fashioned nav radio.
 
John Myers said:
It's a 340. One of the radios is a 750 and the other is a GTR, so they are much different units regardless. When would you use an ILS if you had an LPV approach? To my knowledge there are no airports left with both an ILS and no LPV approach, but I don't know how to definitively verify this.
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It’s the approach in use at a towered airport (big airports still default to ILS), or the goverment is messing with GPS signals again, or lower mins, etc. always thought the more options the better, heck if I could snap my fingers and have a tacan I would.
 
Have a 530,430 wass units. Also use a stratus,foreflight. Hopefully that should be sufficient.
 
James331 said:
It’s the approach in use at a towered airport (big airports still default to ILS), or the goverment is messing with GPS signals again, or lower mins, etc. always thought the more options the better, heck if I could snap my fingers and have a tacan I would.
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Yes but he is talking about a #2 nav


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Juliet Hotel said:
Is that a WAAS GPS that can shoot and approach?
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I would say no... from the manual:

The GDU 1060 and GDU 700 displays can interface to an optional Backup GPS which can be used in the event of a failure of the primary GPS source. The Backup GPS can be used to support the display of time and the ownship on the pilot’s PFD or MFD. The Backup GPS does not provide navigation functions. Installation of a Backup GPS antenna is optional but recommended for the pilot’s PFD if an Integrated Standby System or GBB 54 Backup Battery is installed.
 
You better read the back of your G500TXI manual, right before all the stuff about operating it with gloves. It has a backup GPS, but you lose a ton of functionality including chart georef, etc../.
 
James331 said:
Wasn’t he asking why you’d go ILS when there is a LPV?
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I’m referring to the original question. But mostly I’d personally use LPV if available... but to your point there are times to prefer the ILS. But almost always of course one nav head will do...


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flyingron said:
You better read the back of your G500TXI manual, right before all the stuff about operating it with gloves. It has a backup GPS, but you lose a ton of functionality including chart georef, etc../.
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Don't own it yet, still planning the panel. Wondering about the usefulness of a nav 2. I suspect it would be used zero times and it steals two of the buttons on the GTR, apart from the cost.
 
One Nav could be plenty.

But the day you need it, you'll be completely inept at using it to find an intersection since you're likely to never touch it while all GPS stuff is working.

How much 'extra' is it to have the fully redundant system? How likely are you to stay proficient with it?
 
Ravioli said:
One Nav could be plenty.

But the day you need it, you'll be completely inept at using it to find an intersection since you're likely to never touch it while all GPS stuff is working.

How much 'extra' is it to have the fully redundant system? How likely are you to stay proficient with it?
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That’s what I’m asking, what is the day I’ll need it? I can’t come up with a plausible scenario. I could contrive one, and also contrive a reason to need three alternators and wear a parachute.

One would hope identifying when the needle is in the middle would not require recurrent training, but I take your point.
 
John Myers said:
That’s what I’m asking, what is the day I’ll need it? I can’t come up with a plausible scenario. I could contrive one, and also contrive a reason to need three alternators and wear a parachute.

One would hope identifying when the needle is in the middle would not require recurrent training, but I take your point.
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I'm actually planning to add a standby alternator... But the contrived need is a complete loss of GPS integrity. Doubtful to be certain.

But if you do get kicked back to Nav radios, and you do need to find an intersection, there's a whole lot of twisting in a single radio setup.
 
Ravioli said:
I'm actually planning to add a standby alternator... But the contrived need is a complete loss of GPS integrity. Doubtful to be certain.

But if you do get kicked back to Nav radios, and you do need to find an intersection, there's a whole lot of twisting in a single radio setup.
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I actually view a complete loss of GPS as plausible, but I wouldn't mind working with only one nav on a touchscreen. Not as convenient, but very workable in an emergency situation even without ATC help, which would likely be available.
 
I wouldn't bother with a #2 Nav. There have been pilots that flew IFR with one nav and nothing else. You have an IFR GPS and a ground-based nav receiver, that's the conventional amount of redundancy. An iPad or other portable adds a 3rd level of redundancy for emergencies (arguably, a better one since it has an independent power source).

edit: "two WAAS units and one nav radio" makes it sound like you're talking about 3 boxes, but if your primary GPS navigator and NAV/COM are 1 box then that's not the case, I would consider having an independent second nav.
 
dmspilot said:
I wouldn't bother with a #2 Nav. There have been pilots that flew IFR with one nav and nothing else. You have an IFR GPS and a ground-based nav receiver, that's the conventional amount of redundancy. An iPad or other portable adds a 3rd level of redundancy for emergencies (arguably, a better one since it has an independent power source).

edit: "two WAAS units and one nav radio" makes it sound like you're talking about 3 boxes, but if your primary GPS navigator and NAV/COM are 1 box then that's not the case, I would consider having an independent second nav.
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Yes, that's now my line of thinking. If the GTN 750 bites the dust, I'm back to the backup GPS (which I learned above is no good for approaches), ForeFlight and the com2, which is iffy. So now I'm thinking a GTN 635 is a good idea instead of GTR 225. I will have to lookup if I can operate the transponder and audio panel from the 635 if the 750 dies.
 
John Myers said:
Yes, that's now my line of thinking. If the GTN 750 bites the dust, I'm back to the backup GPS (which I learned above is no good for approaches), ForeFlight and the com2, which is iffy. So now I'm thinking a GTN 635 is a good idea instead of GTR 225. I will have to lookup if I can operate the transponder and audio panel from the 635 if the 750 dies.
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Assuming you are doing something like a GTX345R and a GMA35, the 635 should be able to control the GTX, but only the 750 will control the GMA35, however there is a reversionary mode (assuming everything is properly configured), where if it loses RS-232 from the 750 it would auto-fallback to the other COM. So you wouldn't be able to control any modes, intercom, music inputs, etc, but you should still be able to use the 2nd COM.
 
John Myers said:
It is designed (I believe) as a backup, so I would assume so on both counts although I haven't read the manual.

But in any case, mostly concerned with needing the old fashioned nav radio.
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Better not assume. If your one navigator goes TU in the soup with no VFR anywhere a backup GPS ain't gonna get you down unless it can shoot an approach.
 
My panel has one serious GPS (GNS480, but probably will be replaced soon with an avidyne) and one SL30 (nice modern VOR/LOC/COM unit). I've never felt the need for two GPSs. In fact, I rarely use the nav side of the SL30 but I feel good that it is there..
 
For many years I have had a Garmin GPS 396 panel "AirGizmo" mounted in my Arrow to provide GPS nav info, XM weather as well as audio. The 396 has its own external antenna on top of the cabin and, of course, its own battery so if I lose ship's power totally the 396 will still function and provide navigation to the nearest field. The GNS 530W is, of course, my primary navigator box but the 396 is a decent (and inexpensive) backup as a second GPS. Additionally, the 396 course left-right signal is able to be switched to the autopilot in case the GNS 530W quits. My ForeFlight displaying iPad mini does NOT have the GPS chip BUT I do have the iPad plug-in "Bad Elf" gps device AND a Garmin GLO (GPS and GLONASS) device which will bluetooth to the iPad. Of course I carry the backup SkyNav "Wac Digest" paper plate atlas too :) "Belt and suspenders"...that's me!!!
 
If you are planning a panel with one GPS Nav/Comm, consider that when the display fails you are down. Not so with an SL30 or a KX-155 as a #2. And these are relatively inexpensive.
 
Doug Reid said:
Better do your research. The G500 TXi is advertised as a "display" not as a " waas gps." The decision is yours alone...
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Huh? I know what it is "advertised" as. But the poster asked about using it as a backup to his GPS. I pointed out that while the thing does have an internal backup GPS, the functionality gets quite limited compared to what it displays when it is running on an external approved position source.
 
John Myers said:
G500 TXi has a GPS in it.
Click to expand...

Eh, kinda... But it's only good for navigating along the already loaded route, you can't change the route without the GTN, etc.

John Myers said:
Don't own it yet, still planning the panel. Wondering about the usefulness of a nav 2. I suspect it would be used zero times and it steals two of the buttons on the GTR, apart from the cost.
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What do you mean by "it steals two of the buttons on the GTR?"

John Myers said:
Yes, that's now my line of thinking. If the GTN 750 bites the dust, I'm back to the backup GPS (which I learned above is no good for approaches), ForeFlight and the com2, which is iffy. So now I'm thinking a GTN 635 is a good idea instead of GTR 225. I will have to lookup if I can operate the transponder and audio panel from the 635 if the 750 dies.
Click to expand...

I think a 635 as a backup makes a lot more sense, though for the relatively small price difference I'd probably just make it a 650.

Also, you have tons of panel room in a 340... Why bother with remote audio panel and transponder? I have the discrete panel-mounted units even in my Mooney. IMO, the remote thing is more of a gimmick unless you have a panel that simply has no room for them. @Eggman has dual 750s in his fancy Twin Cessna ;), and still has room for a panel mounted audio panel and dual transponders AND another MFD! :eek:
 
If the GPS signal gets degraded or fails, it doesn't matter how many GPS receivers you have. So you are down to the ILS. I'm building my stack right now and debating the same thing you are. I think I'd like to see two separate nav radios showing me the same thing, so I am pretty sure I'll go with a second Nav Com, the first being an Avidyne 540. I've only got a few IFR lessons under my belt, so I'm very interested in other opinions.
 
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The other option to a second nav is a handheld nav/com. It's totally independent and cheaper, albeit not as reliable.
 
flyingcheesehead said:
Eh, kinda... But it's only good for navigating along the already loaded route, you can't change the route without the GTN, etc.



What do you mean by "it steals two of the buttons on the GTR?"



I think a 635 as a backup makes a lot more sense, though for the relatively small price difference I'd probably just make it a 650.

Also, you have tons of panel room in a 340... Why bother with remote audio panel and transponder? I have the discrete panel-mounted units even in my Mooney. IMO, the remote thing is more of a gimmick unless you have a panel that simply has no room for them. @Eggman has dual 750s in his fancy Twin Cessna ;), and still has room for a panel mounted audio panel and dual transponders AND another MFD! :eek:
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There are the same number of buttons on the com only and com/nav GTR, so they make two of them multi function, which requires an extra press. Not a big deal., but not nothing. I'm a fan of simplicity.

The audio panel is more intuitive to use with the touchscreen. The transponder is as well, with an onscreeen keyboard, although there's really not much difference. I think we'll end up with a discrete transponder though as for whatever reason Garmin charges $1k extra for the remote version. I like the clean look of the panel, but there's really not much difference either way. We do want to keep everything in one stack to reserve the right side for an iPad mount.
 
JohnAJohnson said:
If the GPS signal gets degraded or fails, it doesn't matter how many GPS receivers you have. So you are down to the ILS. I'm building my stack right now and debating the same thing you are. I think I'd like to see two separate nav radios showing me the same thing, so I am pretty sure I'll go with a second Nav Com, the first being an Avidyne 540. I've only got a few IFR lessons under my belt, so I'm very interested in other opinions.
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Two separate ones showing the same thing, or in cases where it's helpful, a second nav to tune to another station to identify fixes.
 
John Myers said:
There are the same number of buttons on the com only and com/nav GTR, so they make two of them multi function, which requires an extra press. Not a big deal., but not nothing. I'm a fan of simplicity.
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Ah, that makes sense.

The audio panel is more intuitive to use with the touchscreen.
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I don't doubt that! I just figure that for the standard audio panel functions (changing what you're talking on and listening to) that the standalone one is much faster. I can do some things by voice on the 350c as well, but I know what you mean on some of the stuff. I kinda wish they would let the standalone audio panel be remote controlled by the GTN as well for the less common/more difficult to use functions. However, I'd want it to be buried in the menu, believe it or not - I really like having the four extra data fields at the top of my screen where the audio panel controls would otherwise be!

I think we'll end up with a discrete transponder though as for whatever reason Garmin charges $1k extra for the remote version.
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Weird... Maybe they figure most of them will go to G1000 users, who must have extra money!

We do want to keep everything in one stack to reserve the right side for an iPad mount.
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Yeah, we're thinking about that too. There's just enough room over there to put an iPad Mini sized AirGizmo mount between the main stack and the breaker panel for us, so if we go to a G500 TXi we would be able to put the EIS screen up on the iPad with one pilot, or have an OK PFD/MFD if there's a second pilot.
 
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