Are Dual NAV's necessary anymore

Jason Larkin

Jason Larkin

Pre-Flight
Joined
May 20, 2019
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39
Location
Zeeland, Michigan
Display Name
Display name:
Larkinja
I purchased a 1967 Piper Cherokee 6 earlier this year. The airplane has a new paint job and a very nice leather interior with brand new carpeting. I purchased a Trutrak autopilot that is going to be installed in the next couple weeks. It has all old avionics and am starting the process of doing some upgrades.

The aircraft came with dual kx170b's, with ils/glideslope. It is IFR current, but one the KX170b's is developing problems. The nav seemed to have died altogether and last weekend the com side could transmit but I couldn't hear anything. A guy on the field gave me a MAC1700 the other day to slide in and it seems to be working fine on the comm side but haven't had a chance to test in the air. The second radio works but has a problematic volume and as long as I get it in the right spot it works fine.

I am currently still on a waiting list at the avionics shop for the ADSB upgrade. I have decided to go with a GNX 375. I also have dual G5's, and a GMA 345 audio panel sitting on the shelf waiting for install as well. For the time being, I am going to leave the KX170b and MAC1700 in.

I am trying to decide what to do about radios. After this round of upgrades is done, I want to tackle the old radios. More than likely looking at a GNC 255A Nav/Com since I am installing a Navigator that doesn't have a com like the 650/750.

My question really boils down to whether or not we really need dual NAV's anymore if we have GPS?

I do not have an instrument rating, but am going to be starting on it soon (basically after I get the avionics up to snuff). Most of the airports around here have GPS approaches. How often do you guys with WAAS find yourself doing non GPS approaches? Do I need to be looking at installing 2 of the 255's? I assume I need at least one! I know that the G5 will work with the 255 in terms of VOR's, GS, ILS, etc, but I assume I can't use 2 radios at the same time anyway and I have never seen anyone with 3 G5's (not even sure that would work). When I was learning to fly, we would tune in 2 vor's for triangulation on cross countries. I could follow one VOR and watch for a flipflop on another one etc.. Instructor would said that's more of an instrument procedure, but I found it fun so I did that sort of stuff a lot. I can't say I have used dual vor's since getting PPL though and VOR's are dropping like flies around here. Could I get away with just one nav and maybe a GNC 225A Com Only for a second radio, or should I have another nav for redundancy flying IFR. I do fly with a portable radio with Nav capabilities so I will have a backup just in case. Let me know what you guys think and if anyone has any advice.

Sorry if this got too long!
 
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Says me, if you have a GPS NAV and a backup, you're good to go. You can always put in a comm radio, they aren't all that expensive. Just so long as you have something to turn to if a box takes a dump in the soup.
 
I'd be more inclined to want a backup gps than a backup nav :) 2 coms is of course, necessary.
 
Arnold said:
What is your tolerance for risk? All the instrument pilots I know insist on 2 Navs & 2 Coms for IMC aviating.
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Zero tolerance isn't possible in aviation, but as close as possible. :) That's pretty much why I pose the question as I am not an instrument pilot just yet.
 
Clip4 said:
For IFR I want 2 separate comm radios, a GPS and VOR/LOC separate from the GPS.
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This pretty much nails it on the head. Since I am getting the 375 installed, my nav/com will be separate from the GPS which I think is a good thing. The nav com will provide the vor/loc coupled to the G5 HSI. So I have all the basics for IMC approaches. Are there fields with localizers but not GPS? The only scenario I can think of is if trying to do an approach with a localizer but no gps and the nav went black and I only had one, then the handheld becomes the only backup and is that smart/legal? My airplane now only has one localizer/glideslope, so I think it's the same scenario. I have a second nav but it is only good for VOR navigation. So right now dual nav's is only helpful with a vor approach which we do have a couple here where that is the only option.
 
Mtns2Skies said:
I have 1 Nav & 2 Comms and I fly IMC just fine.
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Because you've been flying IFR so long. :rofl:

Minimum 2 separate NAV and 2 separate COM for me. I have flown IFR/IMC with a single NAV (VOR CDI) and a single COM, but rather not do it again.
 
EdFred said:
Because you've been flying IFR so long. :rofl:

Minimum 2 separate NAV and 2 separate COM for me. I have flown IFR/IMC with a single NAV (VOR CDI) and a single COM, but rather not do it again.
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Do you have any experience with the G5's? If I were to have 2 nav/coms, would they both feed the single G5 HSI? In almost all steam guage setups, there are 2 indicators making it completely redundant. So referring to your personal IFR minimums, would you then want another redundant G5 HSI?

For the price of a standalone com, they are cheap enough, and I would certainly have 2 coms. Could always ask for a no gyro approach if it really hit the fan. I planned on only having the handheld for worse case scenarios like an alternator fairlure. I'm having a connector installed to connect the handheld to the antenna should I need it. The long term goal is a G3X 10" so then I would have full redundancy in that case, but it might be awhile for that.

So maybe the best bet is a GNC 255A coupled to the G5 HSI, then leave one of the old radios in and still connected to the current HSI until it's time for the G3X. I just hate relying on 40 year old stuff even as a backup.
 
I have a dual G5 unit setup driven off a 430W, but also have a Narco standalone VOR CDI along with an SL40 Com radio. The dual G5 just went in a few weeks ago, before that it was an HSI driven off the 430W along with a standard vac driven AI.
 
Jason Larkin congratulations your airplane sounds great and your approach to equipping it shows you are serious and methodical. Impressive!

Couple of things to consider:
1-Don't put all of your eggs in the GPS basket. Although it is just about perfect and always there you still need alternatives. Few people talk about RAIM yet it should be considered because there are times based on location when GPS signals are not sufficient for navigation. Watch NOTAMS for periods when GPS jammers are being tested. Pay close attention to the distance projections. Be prepared for a bit of a shock.

2-Some approaches require simultaneous monitoring of multiple navaids. To be legal, safe, and smart you need to have the proper equipment. The airlines still configure their aircraft with dual nav/com (including 2 DMEs) in addition to redundant whizbangy FMC/FMS systems.

Good luck on the upcoming installs and upgrades!
 
EdFred said:
I have a dual G5 unit setup driven off a 430W, but also have a Narco standalone VOR CDI along with an SL40 Com radio. The dual G5 just went in a few weeks ago, before that it was an HSI driven off the 430W along with a standard vac driven AI.
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Is that like the NAV-122? That's a clever concept. How do you like the G5's? I'm pretty excited to get mine in!
 
If GPS interference testing is in effect (or a bad actor is jamming GPS for realz), assume that the dozens of primary and backup GPS boxes in your cockpit will be useless. Would you be able to deal?
 
jonvcaples said:
Jason Larkin congratulations your airplane sounds great and your approach to equipping it shows you are serious and methodical. Impressive!

Couple of things to consider:
1-Don't put all of your eggs in the GPS basket. Although it is just about perfect and always there you still need alternatives. Few people talk about RAIM yet it should be considered because there are times based on location when GPS signals are not sufficient for navigation. Watch NOTAMS for periods when GPS jammers are being tested. Pay close attention to the distance projections. Be prepared for a bit of a shock.

2-Some approaches require simultaneous monitoring of multiple navaids. To be legal, safe, and smart you need to have the proper equipment. The airlines still configure their aircraft with dual nav/com (including 2 DMEs) in addition to redundant whizbangy FMC/FMS systems.

Good luck on the upcoming installs and upgrades!
Click to expand...

Thank you! Yes I actually make the RAIM check part of my preflight. I haven't encountered it yet, but I have heard it happening. I know this is much of the knowledge I will be learning and investing in as I progress though instrument. I think many people know a lot of this before they have to make decisions about their own airplane. I, on the other hand, am going to be doing my ifr training in my own aircraft, and so need to make some of these decisions for the aircraft without the experience. I went into this aircraft purchase knowing I would need to go down this road before I leave VFR flying. I ended up well under the budget I set for this aircraft, and so far it's working out well. While it did pass the IFR certification (the previous owner was also a VFR only pilot and so it hadn't been certified in many years), I don't feel it is very reliable in it's current state for IMC. I have talked with my instructor about some of this, but getting a broader range of suggestions from a bigger pool of experienced pilots certainly can't hurt. When I first started on this path of upgrades my head was literally spinning. Starting to feel a little better about the decisions.
 
Dual radio-based navs (VORs)? No. Dual navigation sources? Yes.

When I re-did the panel in my Twin Bonanza, I replaced one NAV/COM with a Garmin GTN625 (GPS only) and a stand-alone Garmin COM radio (no NAV). I kept one of the Narco NAV/COMs as a backup. So I have a WAAS GPS and a separate VOR. 2 independent NAV sources, one GPS, one radio-based. That's more than sufficient, IMHO, especially with an iPad in the airplane too.
 
asicer said:
If GPS interference testing is in effect (or a bad actor is jamming GPS for realz), assume that the dozens of primary and backup GPS boxes in your cockpit will be useless. Would you be able to deal?
Click to expand...

In VFR, absolutely. Unlike a lot of pilots I talk to, I actually found VOR navigation fun and challenging. Many years ago when I started lessons it was a hard subject. Now, I still flight plan to VOR's in foreflight (assuming it's not too out of the way) as I love the math and the tracking. My wife has asked me on multiple occasions why I follow the magenta line on my GPS if I'm not going to go direct. Don't get me wrong, I use my GPS on every flight, but I also like seeing the needle in the middle. I showed her on the last trip that it affected our ETA by 2 minutes and that it's just another way to know for sure where we are. That's how I know my nav radios are starting to have problems. I have a friend I talked to about this just the other day. I asked if he had ever had any issues with his nav equipment and he said "I don't know. Haven't used it in years. I have an Ipad". Yikes.
 
I would want two comms, not sure I would care about a second nav unless that was my only navigational equipment.
 
Jason Larkin said:
Is that like the NAV-122? That's a clever concept. How do you like the G5's? I'm pretty excited to get mine in!
Click to expand...

I forget the model number, but I think it is a 121 without glide slope indicator. The G5s are taking some getting used to. They are a smaller display than either the HSI or the AI. And with all the information on the one unit, there's no need for a scan anymore. I am still doing my normal six pack scan, but there's no real need for it now. The display is taking some getting used to, and I will probably tweak my approach to flying instruments- probably more along the lines of how 121 pilots do it rather than how I have been for the past 15 years - since all the information is presented differently.
 
jonvcaples said:
Jason Larkin congratulations your airplane sounds great and your approach to equipping it shows you are serious and methodical. Impressive!

Couple of things to consider:
1-Don't put all of your eggs in the GPS basket. Although it is just about perfect and always there you still need alternatives. Few people talk about RAIM yet it should be considered because there are times based on location when GPS signals are not sufficient for navigation. Watch NOTAMS for periods when GPS jammers are being tested. Pay close attention to the distance projections. Be prepared for a bit of a shock.

2-Some approaches require simultaneous monitoring of multiple navaids. To be legal, safe, and smart you need to have the proper equipment. The airlines still configure their aircraft with dual nav/com (including 2 DMEs) in addition to redundant whizbangy FMC/FMS systems.

Good luck on the upcoming installs and upgrades!
Click to expand...

RAIM isn't really a thing for WAAS GPS units, unless WAAS isn't available.
 
bradg33 said:
Dual radio-based navs (VORs)? No. Dual navigation sources? Yes.

When I re-did the panel in my Twin Bonanza, I replaced one NAV/COM with a Garmin GTN625 (GPS only) and a stand-alone Garmin COM radio (no NAV). I kept one of the Narco NAV/COMs as a backup. So I have a WAAS GPS and a separate VOR. 2 independent NAV sources, one GPS, one radio-based. That's more than sufficient, IMHO, especially with an iPad in the airplane too.
Click to expand...

Gotcha. So that pretty much sounds like my thought of keeping one of my old nav/coms as backup. Hopefully the MAC 1700 proves reliable enough to act as a backup. That is my only fear. One new nav/com alone isn't super cheap and would rather keep money in the fund toward the G3X than another new nav if I can help it. Thanks for sharing what you did!
 
Ask a crusty pilot and a new Embry student the same question....... The answers will be starkly different.
 
EdFred said:
I forget the model number, but I think it is a 121 without glide slope indicator. The G5s are taking some getting used to. They are a smaller display than either the HSI or the AI. And with all the information on the one unit, there's no need for a scan anymore. I am still doing my normal six pack scan, but there's no real need for it now. The display is taking some getting used to, and I will probably tweak my approach to flying instruments- probably more along the lines of how 121 pilots do it rather than how I have been for the past 15 years - since all the information is presented differently.
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I have heard that is the case. That might also affect how long I go before the G3X! The G5 is required as backup for a G3X install, unless you install 2 G3X's, so this way I am ready for it.
 
Unit74 said:
Ask a crusty pilot and a new Embry student the same question....... The answers will be starkly different.
Click to expand...
I have no doubt about that. I feel I am somewhere in the middle. I took my discovery flight in 1997 when I was a mere 20 years old. I learned to fly when GPS was nothing like it is today and I never really saw an airplane with it anyway. Certainly couldn't use it on a checkride. Even if the airplane had it, the examiner would turn it off anyway. With kids and life I didn't fly for many years. But last year I brushed off the crust, spent 20ish hours with an instructor and then bought my first airplane at 42! Now my 17 year old son is taking lessons. Haha. Life is funny that way.
 
Here's the current setup:
20190809_225135.jpg

You might recognize where this was taken.
 
EdFred said:
My A&P did the install. MayDay is still pushed waaaaaay out on installs.
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Yeah, I'm having the A&P do the G5's too. The 375 has to be installed by a Garmin dealer and they are ALL still way out. Beacon hardly ever even answers the phone they are so backed up. Keep telling me they can get me in soon. I've been on a waiting list for awhile at Mayday, but have a guaranteed date in February. Ugh...
 
I like having dual nav and comm when flying IFR. Do you really need it? No. Is it good to have a back up? Probably.
 
jordane93 said:
I like having dual nav and comm when flying IFR. Do you really need it? No. Is it good to have a back up? Probably.
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Yeah, I think you guys have helped me decide just to keep the older radio in there for now. That should give me full redundancy without spending extra I don't need to.
 
Think your current experience of having a radio on the fritz demonstrate the reason of dual nag/coms, I’d also was the ability to switch my AP to ether nav source.
 
James331 said:
Think your current experience of having a radio on the fritz demonstrate the reason of dual nag/coms, I’d also was the ability to switch my AP to ether nav source.
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I only have 1 nag, don't need 2. HAHA. Sorry just couldn't resist. But yes, that is a good point!
 
No, you don't. You never did, even before GPS. Just had to get that out there. I guess it boils down to your definition of 'necessary.'
 
luvflyin said:
No, you don't. You never did, even before GPS. Just had to get that out there. I guess it boils down to your definition of 'necessary.'
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So what you are saying is that legally we do not need redundancy for ifr? Well I'm an under 200 hour private pilot so just trying to figure out what necessary really means in ifr. Makes sense I guess. You only need 1 mile of vis at my class G field but for me it's "necessary" to have more. When it comes to instrument flying I don't have that same experience. Legal isn't always smart, this much I do know.
 
asicer said:
If GPS interference testing is in effect (or a bad actor is jamming GPS for realz), assume that the dozens of primary and backup GPS boxes in your cockpit will be useless. Would you be able to deal?
Click to expand...
Probability of that is more than zero but also significantly less than the probability of the single lycoming deciding to get quiet unexpectedly which is itself a very low probability. You can really chase your tail down some deep rabbit holes figuring out IFR equipment redundancies. It always seemed kind of silly to go so deep down some of those holes while skipping right over the single power plant hole.
 
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