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GNX 375 Question

Michael Burbidge

Well Known Member
I'm not an IFR rated pilot, but would like to be at some day. So this might be a naive question. Go easy on me.

Does the GNX 375 also require a Nav Radio. I currently only have a COM radio in my airplane. And I'm trying to decide which ADS-B out product to get. The GNX 375 might give me both of those.

Michael-
 
To fly IFR you are only required to have the navigation equipment suitable for the route being flown. So with only a IFR certified GPS you will be limited to in route via GPS and GPS approaches. If relying on only one navigation source is wise or safe is another question. What happens if there are issues with the GPS system? How are you going to navigate then?
 
Nav radio

I?m going through the exact same dilemma on my -7 build. I have two 10.5? G3x screens, a G5, and a GTN 625 WAAS GPS....without the Nav radio. I?m looking into adding the MGL N-16 remote mount Nav radio to compliment my setup. It looks like it?ll integrate with my system pretty easily and be able to be controlled via the G3X touch.

Mark
 
Keep in mind that over 300 VOR?s will be decommissioned by 2025.
G

That second radio is about a LOT more than just VOR navigation. In fact I would say for most of us the VOR receiver in that NAV radio is the lowest priority in terms of functions contained in that box.

When you're stuck in the clag and low on fuel over your destination airport that's suddenly gone to minimums, you're 100% reliant on your GPS to provide approach guidance to get you down through the clouds to the ground. All it takes is one little snafu in the world of GPS (either on-board your aircraft or with the larger space-based system) and suddenly you're in a world of hurt.

That NAV radio gives you the all-important ILS receiver so you can divert to an airport with an ILS (either ILS or localizer non-precision) approach. Without that NAV radio on board you'd better hope you can find an airport that can do a GCA or provide other very precise guidance via radar. Good luck finding one of those when you need it most!

Don't focus on the decommissioning of VORs - if you do, you're losing sight of a major link in the chain of IFR equipment redundancy.
 
The onboard portion of redundancy is easy. There are a variety of low cost GPS units I would be comfortable shooting a emergency approach on like the Garmin 696. The ability to shoot a ILS is great however those are also going to start phasing out. I suspect in 10 years most medium to small GA airports will lose their ILS approaches. As far as I know since GPS was certified for aviation use there has never been a systemwide failure. The chances of the GPS network failing is so low the FAA considers it not a issue.
 
Never say never , I have a garmin 300xl and would likely keep it just for ils. Or I have a king radio is a nav com as well.

The nav com is a kx125 which apparently still brings pretty good money. You can also buy the new still on air craft spruce.
https://m.ebay.com/sch/i.html?cmd=SKW&_pgn=1&_nkw=king+kx+125

The 300xl is an IFR navigator I thought the 150 and 250 were as well but all the listings I see say VFR.
Couldn’t even find a 300xl for sale anywhere
For reference.
 
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. The chances of the GPS network failing is so low the FAA considers it not a issue.

Just 6 months ago I watched an instrument student under the hood shoot the gps approach (vfr) into LVK. First the 650 downgraded from LPV to LNAV, then just before touchdown, displayed a big red X and said ?no gps?. The 650 was working fine. I don?t think the chances are so low at all, although most outages are due to deliberate military jamming tests, or other unauthorized interference. But if it doesn?t work, it doesn?t work.
Something for the OP: While it is legal to operate with gps only, as an instrument student you have another concern: The current practical test standards (I mean ACS) require you to demonstrate 3 different kinds of approaches. GPS can do two. Some examiners will bend the rules, some will not. Something to think about, if you plan to train in your plane.
 
Never say never , I have a garmin 300xl and would likely keep it just for ils. ]

The 300xl doesn’t have an ILS. It’s a TSO 129 (non-WAAS) GPS certified for non-precision approaches, but only when alternate navigation (e.g., VOR-ILS) is on-board.
 
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The onboard portion of redundancy is easy. There are a variety of low cost GPS units I would be comfortable shooting a emergency approach on like the Garmin 696.

Whether we have two or 10 GPS units on board, we do not have redundancy. We are completely reliant on GPS. A search on this forum will reveal several instances where the wonderful Garmin GA35 antenna failed in a manner that turned it into an active on-board GPS jammer that took out every GPS receiver on the airplane. That's just one example of a failure that can take out GPS.

The long and the short of it is that redundancy is best achieved through having multiple disparate systems, not multiples of the same system.

Yeah, ILS is old school - I get that. Still, it's the only on-board precision approach alternative we have to GPS-based approaches. If you're really thinking about the "what if" scenarios we really, really have to look hard at that big question... "What if GPS fails?" Because it DOES fail.
 
GPS Fails

I heard all this when I decided to only have GPS IFR capability in my plane. How come nobody ever talks about radar vectors? And always have plenty of fuel so you can get to somewhere where they can get you down through the clouds. I have breifly lost my GPS signal once and it was from military testing. I have never heard of a prolong outage
 
I heard all this when I decided to only have GPS IFR capability in my plane. How come nobody ever talks about radar vectors? And always have plenty of fuel so you can get to somewhere where they can get you down through the clouds. I have breifly lost my GPS signal once and it was from military testing. I have never heard of a prolong outage

Like Bob warned in an earlier post, don't get hyper focused on the enroute portion of the flight. While not legal, just about any GPS solution will get you to the destination. However, they may not present information to shoot the approach safely to minimums in IMC. If you have a GPS navigator that only meets the older TSO (i.e. GNS) you are required to use a different technology to shoot an approach at your alternative.

If you are planning on flying IFR, it's more than just popping up and down through a cloud layer. You need to understand what hardware is required to fly to minimums for each type of approach and at your alternate. Then decide which of those solutions you need in your aircraft.
 
Certainly having a VOR/ILS is nice. I have however never had a GPS failure in flight except in war zones where jamming was ongoing. I have however had numerous ILS failures from onboard equipment issues to ground issues. I guess one difference in how I view things is I don?t consider a RV as a hardcore IFR machine. If the weather is going to be at or near minimums I am going to have enough fuel to get somewhere nice. If I will have to transit a freezing layer IFR I am going to buy a ticket and park the RV.
G
 
+1 on what "G" posted. I've had a GNS430 installed in my Bo for 16 years and since installed I've never shot an ILS or needed VOR for nav. I fly almost exclusively IFR. I decided not to put VOR/ILS in my RV8. In seven years I haven't missed it. If you lose GPS due to installation that's another issue that can (and does) happen to VOR/ILS.

I realize this is anecdotal info. Also, anecdotally, I've noticed that when the military has disabled GPS locally the weather is VFR. YMMV
 
The 300xl doesn?t have an ILS. It?s a TSO 129 (non-WAAS) GPS certified for non-precision approaches, but only when alternate navigation (e.g., VOR-ILS) is on-board.

I never fly ifr in this plane and rarely use the gps but three people took their ifr In it so I assumed the 300xl was what qualified, it's non WAAS that's correct and will fly non precision approaches. Being that you need to show a precision approach I assumed it was with the 300xl they did that.

I rarely use the 300xl as anything but a com and currently fly exclusively VFR in it. Thanks for the clarification on that.
 
I never fly ifr in this plane and rarely use the gps but three people took their ifr In it so I assumed the 300xl was what qualified, it's non WAAS that's correct and will fly non precision approaches. Being that you need to show a precision approach I assumed it was with the 300xl they did that.

I rarely use the 300xl as anything but a com and currently fly exclusively VFR in it. Thanks for the clarification on that.

Didn't you also say it had a KX125 installed? If so, that is how they did it....
 
That is correct I'd 125
Figured that was it if it wasn't the 300xl. Sad that I've owned the plane for a couple years and not used the nav/ approach functions on either but when you typically fly only when it's 5000 ft or better and unlimited you don't get much need for it. Lol
When I flew for my ifr training it was in a club plane that was far better equipped.
 
"What if GPS fails?" Because it DOES fail.

How about:
- a portable COM/NAV radio with ILS/LOC reception, always fully charged in your flight bag, and
- a BRS parachute

I'd bet a $1 that if you intersected the total number of approaches to minimums in all of RVs with the total number of GPS outages ever you'd end up with a likelihood orders of magnitude lower than bird strikes. Our risk perception is a funny thing...
 
GPS approved for IFR

Be careful on what GPS you pick for IFR approaches. The TSO for that GPS may require a separate navigation source such as a VOR / ILS to be legal for a GPS approach. Just because we have an experimental airplane does not mean that we can use what we want. To be legal in the IFR system, we need the same navigation radio(s) that the the certificated airplanes do. IF you think we are legal with a non-TSO radio, please show me a link to the regulation that allows it.
 
Fair weather alternate

I agree with Aluminum. I fly IFR for a living and commute to and from the jet in my -10. I had a Grumman Tiger for 10 years before the -10. I have never seen the time when an ILS was needed to save the day. A fair weather alternate is a must.

It is foolish to fly IFR with widespread near minimums weather in any single engine plane. Please understand and respect that our small planes are NOT all weather capable and never will be regardless of avionics or redundant power sources. The ability to fly IFR is priceless but that does not mean we have little or no limitations as to when or where we should fly.
 
A back up is always good, most home built aircraft don?t need a a ILS receiver as a back up. A simple VOR should be enough. Only if you are planning on routinely flying to 200/1/2 would a ILS backup make sense. Again cost and complexity have a big say. You could put in a 375 and a 650 and be well backed up.
 
Back up ILS

A side note.Most LPV approach minimums are higher than an ILS DA or DH. Having said that we're talking 300' vs 200'. Still pretty darn low.
 
Solid point

How about:
- a portable COM/NAV radio with ILS/LOC reception, always fully charged in your flight bag, and...

Emphasis on FULLY charged. Not something I fully appreciated. I'll spare everyone a repeat of my saga. :)
 
Tried it once

Have any of you actually flown an ILS approach on the portable Navcom radios?
Just wondering....

Yes. I'd say it was like bringing a .22 to a gunfight: not perfect gear for the job, but vastly better than nothing.

Meanwhile, I've flown a non-precision GPS approach with a Garmin G5 and an iPad running Foreflight. Obviously that combo isn't legal for IFR, but it's very very functional in a pinch, probably easier than using a 430.

The 430 is miles ahead of an iPad in terms of reliability, obviously. My 430 has never crashed on me once. My iPad definitely likes to take a nap every now and then.
 
:eek:Had VOR/GS/LOC/MB in my old RV-4. I flew IFR rarely. It came in handy a few times for IFR departure to VFR or IFR letdown through under-cast. No GPS approaches or area navigation, e.g., ATC go direct to a way point that you cant track to with your VOR, you can't accept. You could decline direct waypoint clearance and ask for vectors. In certified planes I used a handheld GPS as secondary situational awareness flying NDB approaches.

Commuted for years in a Tomahawk with only VOR/LOC and MB. VOR approach was all timed, VOR on the field. LOC had MB at FAF. If it was low I did not go... This was before IFR GPS were available. Now most NDB/LOC and MB have gone bye bye for GPS approaches. GPS is far better of course. However ILS is still the mac-daddy of approaches, can get you to 200 HAT and 1/2 mile or 2400 RVR and pretty commonly available. That is low, However GPS with WAAS can now achieve it. Not that common yet, and GPS LVA does not give your vertical guidance, so it's not really percussion. (Correct me if I am wrong)

I may not go IFR on current project. I'm sure some folks are flying IFR with non certified GPS.... don't do it. My bottom line are you really going to fly IFR? I suggest put in previsions and add later. BY ALL MEANS have attitude instrument flying instruments and PRACTICE using them (with safety pilot and hood).

Now many RV's have one or two axis autopilots as a norm. Those will save your bacon, and I say almost mandatory for safe SINGLE PILOT IFR... Hand flying an RV in clouds single pilot can be a handful. If you get in an unusual attitude it will WIND UP FAST!!! Not good IMC. You are adding $10K or more to your panel to get IFR GPS and Autopilot... How much will you use it? My guess is not $10K worth. It is up to you and of course if not equip you will have much higher mins to fly to avoid IMC. If you fly local you can stay on ground. If you go XC a lot, a special VFR departure may get your travel day started early.
 
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:In certified planes I used a handheld GPS as secondary situational awareness flying NDB approaches.

However ILS is still the mac-daddy of approaches, can get you to 200 HAT and 1/2 mile or 2400 RVR and pretty commonly available. That is low, However GPS with WAAS can now achieve it. Not that common yet, and GPS LVA does not give your vertical guidance, so it's not really percussion. (Correct me if I am wrong)
.

I recall when aviation gps?s came out. All you needed was a good ground track, and suddenly you could fly NDB approaches to right over the runway with any piece of sxxx ADF. Of course the gps was for position awareness only :)

I haven?t done a survey, but I?ll bet nearly every runway in the US with an ILS now has a GPS LPV approach, with most of them down to 200 and 1/2. Then there are lots of gps approaches at runways without an ILS, with slightly higher minimums due to the need to see the runway environment where there is usually not an approach light system.
LPV approaches do have vertical nav guidance.
 
I agree. And I don't think this is limited to RVs.

My first and only RV10 instrument student: On our long x/c I had him hand-fly the first 2/3, including an ILS with ceiling 200? (vis underneath was >1). He did fine. On the last leg I let him use the autopilot, and he remarked how less stressful it was. OTOH, on his check ride, he failed the coupled approach task, when the autopilot flew thru the final approach course. The very next day we repeated the same approach, and were unable to duplicate the failure. We could only conclude that he pushed or didn?t push the right button at the right time. So autopilots are great, but they do add complexity. And the PIC should certainly be capable of flying in IMC without it.
 
Have any of you actually flown an ILS approach on the portable Navcom radios?
Just wondering....

I have the original Sporty?s handheld, which offered digital bearings to-from a VOR, only. No needles, no ILS. I did a few VOR approaches under the hood, using just the portable, and it wasn?t too hard. I think it helps if you?ve done some NDB approaches - same sort of visualization (only easier) required.
 
My first and only RV10 instrument student: On our long x/c I had him hand-fly the first 2/3, including an ILS with ceiling 200’ (vis underneath was >1). He did fine....And the PIC should certainly be capable of flying in IMC without it.
I'm a CFI Inst Multi, 1600 dual given. I don't actively teach now, but I agree a pilot should be able to hand fly without an autopilot in IMC. However dual instruction isn't really single pilot IFR. You're not going to let him screw up, where if he is solo, nobody to back them up. I flew part 135 in a light twin single pilot, the workload could be very high. I recall the OP Spec required a working autopilot.

I don't know how the rv10 flies, but I'm guessing it's a little more stable than the 2 plc birds. RV's are a delight VFR or IFR, they do what you want with light balanced controls. There is no real issue flying IMC with an RV. My point is they are clean. You inadvertently get too high bank or nose low pitch it will go Vne quickly.

Autopilot is the copilot. It allows you to do management, planning, communication, without also having to keep your scan up and control the aircraft. Even on autopilot you should keep your scan, but having hand off stick reduces the physical and mental workload verses hand flying. I have seen many students reach over to switch the frequency on the radio, and put the aircraft in a bank, due to momentary loss of scan and reaching with one hand with their other hand still on the yoke. There are techniques I taught to avoid that. However flying is your number one job and you only have a little extra bandwidth to do other tasks, which you have to divide up. Autopilot is a super nice thing to have to reduce workload, which does increase safety. My first flying job was in the metroliner, two pilots but no autopilot.

Agree you need to be proficient in autopilot use and monitor it's doing what you want. You can't just push a button and look away. You need to verify the mode it is in. The larger more sophisticated planes have a FMA or flight mode annunciation. That was your go-to scan item to make sure you were in the proper autopilot mode. Didn't matter what button you punched or what you thought it was doing the FMA was what it was really doing.
 
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Autopilot is the copilot. It allows you to do management, planning, communication, without also having to keep your scan up and control the aircraft. Even on autopilot you should keep your scan, but having hand off stick reduces the physical and mental workload verses hand flying. I have seen many students reach over to switch the frequency on the radio, and put the aircraft in a bank, due to momentary loss of scan and reaching with one hand with their other hand still on the yoke. There are techniques I taught to avoid that. However flying is your number one job and you only have a little extra bandwidth to do other tasks, which you have to divide up. Autopilot is a super nice thing to have to reduce workload, which does increase safety. My first flying job was in the metroliner, two pilots but no autopilot.

Agree with the above 100%, no way would I depart IFR without the AP. When things get busy, hand flying in actual can be very challenging.
 
I remember watching a VCR tape by Richard Collins a few years back...ok, maybe it was couple decades...anyway, he said something that really stuck with me: “never fly into IMC as a single pilot”. He went on to explain that meant either have a working AP to help fly the airplane, or a pilot in the right seat doing the same. I have and continue to operate by this motto.

So, I agree completely as well that I would not take off into IMC without a working autopilot if I’m by myself or don’t have another proficient pilot in the right seat. However, that’s not the same as just flying IFR, which I do nearly every flight when I fly cross country regardless of weather conditions.

I’ve been doing GPS approaches for many years and my Garmin Pilot logbook shows 2128 of them. The last RAIM failure I had was in 2006 on approach in to Offutt AFB with a King 94 GPS unit freshly installed in our AeroClub Baron. Since then, aside from testing in progress, I’ve never had a GPS failure - the system is extremely reliable with a statistically much higher up time than either a VOR or ILS system - significantly higher, as in 6 sigma high, 99.999999 uptime. This goes along with Bob’s comment earlier about GPS failure during testing. It happens. However, all testing is NOTAM’d, so be informed before you fly. And if you’re doing an GPS approach in actual instrument conditions, the magic words to stop or inhibit testing caused failures are “STOP BUZZER”. Simply tell ATC this and they are required to immediately cease testing. I’ve done it and it is effective; I did end up going around and re-performing the approach, but it worked out fine.

I would not go buy and install a NAV unit just because of the “what if the GPS constellation failed?” line of thinking. You only need 3 satellites to navigate laterally and 5 satellites to do WAAS navigation (which includes an LPV approach). The next time you’re at your GPS, take note of how many active satellites are in the sky and available to your unit...something around 12-15 generally. Now consider how many of those would have to fail to limit your approach.

The decision really comes down to your mission. For my little RV12, I have a GTN 625, which is essentially the same thing as the new GNX 375, minus the cool transponder stuff. And I’ve flown almost 200 approaches with this so far sans a NAV radio without issue.

I’ll add that I don’t have a second COM either. My thought is that everything required by 91.205 is a starting point for what is essential, and then pare it down to only what is needed for “aviate, navigate and communicate” (which isn’t much); after that, if my radio failed, I’d just squawk 7600 and go land somewhere using that minimum 60 minutes of fuel reserved just for this purpose. It gets down to what is essential, and your definition of essential; mine is to be able to find somewhere to land safely. So Aviate, Navigate and then communicate.

My opinion is that a GNX 375 would be a fine single IFR navigation device for your RV. Just be aware of it’s limitations and risks and then plan accordingly.
 
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My RV-7 is VFR only for now but I hope to add an IFR GPS in the future just so I can file if I need to deal with some clouds. I don't plan to do a lot of hard core IFR flying. For that reason I won't be installing a full Nav/ILS radio setup.

To gmcjetpilots point, think about how much IFR flying you might actually do. How often do you plan flying in weather where you'll be shooting approaches to minimums with no clear weather alternate? Let that guide your decision.

Totally agree on the AP. During my training I hand flew everything but would seriously hesitate to do much instrument flying other than climb thru a thin layer without one, especially in an RV.
 
ILS with GPS on the 375?

Guys, resurrecting this thread for another kinda related question ;)

Still getting acquainted with the 375 I bought and installed a couple of years ago, and only few fields ILS equipped around here. These are expensive, as in check my location, and loads of traffic making experiments difficult for me.

LPVs and RNAVs are one thing the navigator is made for… still the manual mentions ILS and states: Selecting an ILS or LOC approach results in a pop-up message. Activate the approach or select a different one.

What does happen if the “ILS” approach is activated?

Thanks for any feedback.
 

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It provides GPS approach guidance designed to keep you on the ILS centerline and GS. And imho it works well. But note the caution: using this as primary guidance is not legal for an ILS under IFR.
 
thanks for that super quick answer Bob.

Just never had a chance to try out that function. And yes, I have a separate ILS receiver :)
 
Guys, resurrecting this thread for another kinda related question ;)

Still getting acquainted with the 375 I bought and installed a couple of years ago, and only few fields ILS equipped around here. These are expensive, as in check my location, and loads of traffic making experiments difficult for me.

LPVs and RNAVs are one thing the navigator is made for… still the manual mentions ILS and states: Selecting an ILS or LOC approach results in a pop-up message. Activate the approach or select a different one.

What does happen if the “ILS” approach is activated?

Thanks for any feedback.
Dan 57,

If you load and activate an ILS approach on the GNX 375 GPS navigator, it provides lateral navigation for the entire approach (including the missed approach), but no vertical (glideslope) navigation.

You would, of course, need to switch to your VOR/ILS navigator prior to the FAF to receive vertical guidance to descend on the ILS.

Steve
 
Roger that Steve, thanks.

I’ll try to fly to neighboring France next week or so and shoot a couple of good ‘ol fashioned ILS and verify what the 375’s doing. Lat NAV would nevertheless be good for a MA as my main ILS receiver ain’t route able, just rough GS/LOC. Could take vectors/own line-up on the 375, then use the real ILS for the app, reverting to the 375 in case of MA…
 
The ability to shoot a ILS is great however those are also going to start phasing out. I suspect in 10 years most medium to small GA airports will lose their ILS approaches.

I disagree. ILS is the only back up that we have. VORs and NDBs are going away, except for limited enroute support. Many airports have dropped their VOR approaches eventhough the VOR supporting them is on the MON list. I suspect that any airport seeing meaningfull commercial traffic, including small jets will still have ILS for a long time. Remember, a GPS outtage can affect airports for 100's of miles, well outside the normal reserves carried. If they jam a signal, even accidentally, where do the birds with paying passengers go. The FAA would never allow a situation where their cost cutting results in 10's or 100's of passengers to die because of it. Just imagine the press once they figure out that keeping the ILS in place would have saved those lives. They may not care about us individual pilots, but they care a lot about helpless passengers.

The only other alternative at the moment is ASR's and I suspect that the training and recurrency costs far outweight the iLS maintenance costs. Ground equip failures are not comparable, as there is often an alternative in the immediate vicinity as failures are isolated to one airport.

Larry
 
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