Avionics Report

October 2019 Issue




Checklist

- Ditching the VHF nav means no more costly upkeep of aging antennas.
- Investing in Garmin’s new budget IFR WAAS navigators gets you the absolute latest in GPS tech.
- But without VHF nav, they lack the VOR/LOC/ILS redundancy you might never need.

Is VHF Nav Dead? For Many, It Could Be

Garmin's new line of IFR navigators ditch the VHF nav receiver in favor of WAAS GPS. That's sparked a debate of whether ground-based nav is history.

Once upon a time, the well-equipped instrument panel sported two identical 760-channel King KX155 radios with VHF comm, VOR, LOC and ILS-the cat's pajamas. We needed two navs for cross-radial fixing and we needed two comms for ease in picking up the weather. Plus, let's face it; overall we needed two radios to make sure at least one of 'em worked.

But that dual navcomm mindset so permeated our culture that it remains the norm today. Even new panels today will typically include two identical GPS navcomm boxes, or one large and one small. The reality is that modern avionics have largely mitigated the reliability problem. We can still certainly make use of two comms, but do we really need dual GPS and dual VHF nav? In fact, do we really need VHF nav at all? Let's talk about this.

Practicality: Vhf Nav Today

26 RNAV BUY LEDE

The finger walking on the Garmin GNC 355 mapcomm pictured here is loading a precision GPS approach—the only ones available in Garmin’s latest line of retrofit navigators.

Be honest. If you have a certified WAAS GPS in the panel, when was the last time you navigated using anything other than GPS? Even without a certified box on the panel but with something in your lap, when was the last time you used VORs as your primary means of cross-country nav? Either way, when was the last time you flew a VOR, LOC or ILS approach?

I fly about 120 hours a year, in all weather. I checked my logbook. My last VOR and ILS approaches were during my last instrument proficiency check (IPC). Before that, it was on the prior IPC. I kept looking further back in my logbook and after five years I gave up; I didn't find any VHF approaches outside of an IPC. I'll bet you'd find the same.

OK, I'll even take it one further. When was the last time you did the 30-day VOR check required by 14 CFR §91.171(a)(2)? This year? Probably not. OK, then, without that 30-day check, you're not legal to use VORs for navigation under IFR. Tell me again: Why do you have one of those in your panel, let alone two?

Let's have a reality check, shall we? I'm a lot like you. I have two VHF nav radios in my airplane, and of course, two VHF radios. I just have one GPS, though, having recognized the wasted money in having two. (See the sidebar.) But, not to toot my own horn or anything, I actually do those VOR checks. No, I don't do them every 30 days because I don't always fly every 30 days. But, I do one early in nearly every trip. This way, should I ever need to use that VOR, I'm legal to do so.

Now, that brings us back around to the main point. VHF nav today in general aviation in the U.S. is primarily useful as a backup to GPS. I live in the southwest, where we get GPS interference NOTAMs nearly every week. So, yes, I have need to back up my GPS occasionally. I keep a nearby VOR tuned in and when the GPS signal goes away, I'm ready.

Still, though, that only takes one since I've also got DME (for reasons that might someday find their way into a separate article), so having two VORs is unnecessary. If you ever need to identify a cross-radial fix using VORs and you don't have DME, chances are amazingly high you could just ask ATC and they'd steer you as needed. And, if you needed to do that because GPS is out, well, they'd probably lead you by the hand wherever you needed to go.

What about on approach? With WAAS permitting GPS approaches with LPV minimums often the same as an ILS, again we can default to GPS nav. So, what's the difference and do we care?

Gps versus Vhf Nav Approaches

27 RNAV RWY 8

All GPS approaches essentially follow one of a couple different design models that are virtually the same when you hit the final approach fix. Whether or not you have vertical guidance is primarily dependent on the terrain and obstructions. The technique for flying any of the GPS approaches is essentially the same. Even those without published vertical guidance like LNAV/VNAV or LPV often have LNAV+V simulated vertical guidance provided by the box, so you rarely have to worry about those pesky step-down fixes requiring a "dive-'n-drive" technique like you might on a VOR or LOC approach.

So, given the choice of a VOR or even LOC approach versus the typical GPS approach, most of us would rightfully choose the GPS approach every time. Adding LPV precision minimums on GPS approaches brings the comparison to ILS versus LPV, allowing us to essentially disregard VOR and LOC approaches.

28 LOC rwn 8

When it really counts, an ILS and an LPV approach both get you down to the runway, usually offering similar minimums, and the skill needed to fly one is the same as the other. In fact, the LPV is a bit easier to fly with less button pushing and knob twisting, and-especially with an autopilot-is more seamless in the transition from the enroute phase. In fact, LPV and ILS approaches have similar design criteria. Study the LPV and ILS approaches to Lancaster, Pennsylvania's Runway 8 on the charts shown above.

Overlapping design criteria often end at the runway. The missed approach segment can differ significantly in ways that really don't much matter to us here other than the ILS often requires more machinations to get navigational guidance on the missed than any GPS approach. Note, though, that the missed approach design considerations for each can affect the minimums.

The bottom line, here, is that with 1549 Category I ILS approaches compared with 3998 RNAV (GPS) approaches with LPV minimums, and many more with higher minimums, there's little operational advantage to VHF nav, either enroute or on approach-so long as everything goes according to plan.

The main use today for VHF nav is as a backup to GPS. When GPS is unavailable or can't provide the needed precision, we've still got those VORs and ILSs. But, with the FAA planning on a GPS future both for our own navigation and for their surveillance, they're planning to decommission a great number of VORs and ILSs in the coming years, leaving us with the Minimum Operating Network capable of getting us safely on the ground, but not necessarily where we're going. So, while GPS is planned to become our near sole source of navigation, the opportunities to even efficiently use VHF nav as a backup will dwindle.

With that as an indictment of VHF nav, there remain a couple practical considerations. For arcane reasons, no GPS approach officially qualifies as a "precision" approach. Instead, at best their classification is an approach with vertical guidance. Today, only an ILS (or an LDA/GS, essentially the same thing) is considered a precision approach. This affects our choices when filing an IFR alternate.

29 GARMINS NEW GPSCOMM

At roughly 2 inches high, Garmin sized its new budget GPS series to fit in place of traditional navcomms like the King KX155.

Finally, there's one last consideration about VHF nav that few of us consider. Remember the old days when you often listened to FSS over a VOR frequency while transmitting on an unrelated frequency? Well, that's still possible, although the need (especially with cellphones) nearly-but not completely-disappeared.

I've flown into Allendale County Airport in South Carolina a few times. On the ground, I got very limited cellphone coverage and I couldn't raise ATC on any radio, in spite of a published frequency. The Chart Supplement tells me to contact Anderson Radio through their remote communications outlet on 122.1 while listening to the on-field VOR on 116.7. While this is unusual today, it still remains a possibility that could leave you unable to contact FSS to reach ATC if you don't have VHF nav.

Should You Buy Dual GPS?

30 DUAL- IFD

Aside from the central issue of the VHF nav question, let's diverge for a moment to look at dual GPS. What good is it to have two? This is kind of a pet peeve of mine, so forgive me if I rant for a moment, away from the main point.

Be honest: The main reason most of us have dual GPS is because of the mindset that we needed two VHF navs back in the day-and also because Garmin changed the face of the traditional navcomm with the all-in-one GNS 430/530. Buyers bought them in pairs and still do so today with the GTN series and also the Avidyne IFD units, shown here. The day of two VHF navs is long past, but is there anything you can do with two GPS boxes that you can't do with just one (aside from the added screen real estate)?

I'd submit that the answer is that having two is mostly pointless, other than redundancy and possibly using the second box to have a different display, which actually might be better suited on an MFD anyway. But, having two GPS navigators behind those screens buys us nothing. (To be fair, there are some ways to use two GPS boxes, but those are edge cases that escape the average Joe Pilot.)

So think about that the next time you're considering a panel upgrade and complaining about the cost. Consider dropping that second GPS/nav/comm in favor of … what?

To answer that, consider what you use and need the most. We'll help you with your choices back in the main article.

-Frank Bowlin

Equipping Today

As interesting and engaging as this whole concept is in a theoretical sense, Garmin's introduction of essentially the same high-end GPS that they use in their flagship GTN navigators (with a couple feature differences), put in a smaller-box standalone (GPS 175), or paired with an ADS-B transponder (GNX 375) or with a comm (GNC 355)-but none with a VHF nav-has moved the discussion into the practical. If you're doing a panel upgrade now, what should you do?

The answer to that largely depends on your flying and the current state of your panel. There could also be antenna considerations, and on some airframes VHF nav antenna work is expensive. We'd probably not replace a perfectly good existing radio with a VHF nav. It would be good to retain that VHF nav as the backup or for alternate planning as we discussed above. Beyond that, it all depends on your budget and on your use.

Surely, if you don't fly under IFR, you can safely skip VHF nav with little consequence. But, you probably already have working VHF nav, so it might make sense to just leave it.

Assuming you're considering your options because you don't even have GPS and haven't equipped yet with ADS-B, the GNX 375 GPS/ADS-B transponder ($7995) might be a good choice to replace your existing transponder and add a state-of-the-art IFR GPS. Retaining your existing navcomm(s), assuming they're working well, preserves all your options while adding ADS-B In and Out and a WAAS GPS.

Or, perhaps you've already got ADS-B Out, but you don't have WAAS GPS (except internal to the ADS-B box) and you want to be able to fly those GPS approaches. You could add the GPS-only Garmin GPS 175 ($4995) and retain everything else.

Or, perhaps you've got ADS-B Out but want to simplify your panel while adding WAAS GPS. Add the GNC 355 GPS/comm, ripping out at least one of your existing navcomms.

These, of course, are just hypotheticals. Note that this doesn't address interoperability. These new boxes do have good interface options. As we reported in the GPS navigator roundup in the September 2019 Aviation Consumer, Garmin's new units work with a variety of third-party nav indicators and autopilots. Still, you should check to make sure that what you expect to retain will talk as needed to what you'll add.

Also note that other than the convenience and display sharing (for ADS-B In data), and unless you're really tight on panel space, there's little advantage of having a transponder in the same box as your GPS. But having a comm in the same box allows frequency selection right from the GPS database, which can be a big convenience.

Finally, you might note that a discussion of doing without VHF nav led us to various equipage options, many of which retained at least one existing navcomm. So even with these new options, you won't necessarily be completely without VHF nav capability. But the GNC 355 GPS/comm does have a frequency monitoring capability that lets you select a main frequency and monitor another. It's not quite like having two independent comms, but it's not a bad compromise if you really need to save space or money.

Bottom line is that in most cases you wouldn't be without VHF nav, but you could pretty safely choose to be.

Contributor Frank Bowlin is the Editor of sister publication IFR Magazine, where he noodles these kinds of buying decisions all the time.