For safe instrument flight, skills are obviously an essential requirement. But the knowledge component is critical – and often underappreciated. Here are some common weak areas from recent checkrides and IPCs as well as resources to keep you sharp.
If you are still treating GPS as a new navigational system, get over it. The first FAA-approved IFR GPS navigator went into service on February 16, 1994; it’s OLD! The regulations are now written “backwards,” defining only the times when you cannot (legally) use GPS (all other times go for it). Some pilots still err on the side of caution chasing wobbly VOR needles for conventional approaches. Life is a lot simpler (and safer) with the steady guidance of GPS and a vertical path indicator. There is a reason they called all those older approaches “non-precision!” Click HERE for a fact sheet on newer RNP approaches. (More FAA Fact sheets HERE.)
The basic legal guidance for GPS usage is in AIM Chapter One, Section Two. The ICAO term for this class of navigational magic is “Performance Based Navigation” (PBN). Instead of referencing the sensor systems, PBN only specifies the required accuracy for the system. Use whatever you like so long as it provides the “accuracy, integrity, continuity, availability, and functionality needed for the proposed operation in the context of a particular airspace concept.” (And of course it must be FAA-Approved) The guidance is straight forward for enroute operations, but gets a little muddier starting downhill.
AIM 1-2-3(C) Uses of Suitable RNAV Systems. Subject to the operating requirements, operators may use a suitable RNAV system in the following ways.
1. Determine aircraft position relative to, or distance from a VOR (see NOTE 6 below), TACAN, NDB, compass locator, DME fix; or a named fix defined by a VOR radial, TACAN course, NDB bearing, or compass locator bearing intersecting a VOR or localizer course.
2. Navigate to or from a VOR, TACAN, NDB, or compass locator.
3. Hold over a VOR, TACAN, NDB, compass locator, or DME fix.
4. Fly an arc based upon DME.
Search the footnotes in section 2, for more detail and you will do great with hangar flying discussions – or checkride questions – regarding what is legal to fly with your panel-mounted WAAS unit. Obviously “legal” also requires careful verification of databases, manuals, updates, and satellite NOTAMs. This makes preflight and programming a little longer, but the safety and precision make it worthwhile.
So yes, your G-1000 or WAAS GPS can navigate conventional (ground-based) VOR approaches even if “GPS/RNAV” is not mentioned in the approach title. The FAA still requires the navaid to be operational and you must actively monitor it. Your PFD can be GPS/magenta, just keep a VOR source operational/visible. You can even legally navigate all the legs on an ILS right up until just before the final approach fix before switching to “green needles.” In fact, some newer PBN ILS approaches *require* GPS for transitions to final. This is certainly a critical item to ascertain in the pre-brief phase of your flight.
Dig deeper into AC90-108 “Use of Suitable RNAV Systems on Conventional Routes and Procedures” for trickier questions and deeper knowledge. And even better, consult AC 90-119 (still in draft form) for future developments. This AC collects RNAV rules from numerous scattered sources. The YouTube below from Bruce Williams on conventional approaches summarizes all the requirements nicely. This site is a reliable source of IFR wisdom HERE.
With all this focus on the detailed rules regarding GPS, it is important to remember that the GPS constellation can go out of service. Consider your situation if it is suddenly unavailable. (BTW, any jamming is expressly prohibited by the FCC – the people who brought you 5G). GPS has become our “invisible utility” that runs modern society. Cell phones, energy companies and even the stock market depend on GPS (time stamps and system synchronization). So what would happen if we were up in the clouds and GPS went out?
FAA Navigational Redundancy: MON
The FAA has a plan for this and has extended the service volumes of many VORs to create a system called Minimum Operating Network (MON) using only ground-based navaids. If you noticed some jacked-up high-power VORs around, you are looking at it!
the FAA is retaining a limited network of VORs, called the VOR MON, to provide a basic conventional navigation service for operators to use if GNSS becomes unavailable. During a GNSS disruption, the MON will enable aircraft to navigate through the affected area or to a safe landing at a MON airport without reliance on GNSS. Navigation using the MON will not be as efficient as the new PBN route structure, but use of the MON will provide nearly continuous VOR signal coverage at 5,000 feet AGL across the NAS, outside of the Western U.S. Mountainous Area (WUSMA). AIM 1-1-1
Keep Learning! New Gold Seal IFR Ground School (Free to CFIs)
Aviation requires us to stay up to date with the continuous changes in knowledge and technology. But nowhere is this more important than with instrument flight (as illustrated above). Every detail counts. Why did they put those two asterisks next to the minimums on that ILS mins? What does that snowflake above mean (Santa)? Preparing for an instrument flight (or preparing for an IFR oral) you have to be totally tuned up and curious to be safe.
SAFE MCFI Russ Still has been working diligently last year researching and building a totally new instrument ground school course. And all his courses are free to CFIs! Every CFI (and any committed pilot) should watch this new course – I guarantee you will learn something new. His fresh animations and content are visually captivating and very worthwhile (and CFIs can track their student’s progress 
on the Gold Seal portal). Russ is a talented and committed educator. He really dug into the details and kept a lot of DPEs busy with his detailed questions. The Gold Seal team created an amazing course; try it here (FREE to CFIs). And for everyone else, the free Gold Seal “Know It All” pdf is an excellent review. Fly safe out there (and often)!
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The AC that will change guidance on PBN, RNAV, etc. is AC 90-119 (you wrote it as 90-118, probably just a typo). My summary of the draft is at my blog: https://bruceair.wordpress.com/2021/05/17/draft-ac-90-119-performance-based-navigation-operations/
You can also find video of a presentation about PDN, RNP, RNAV, etc. on my YouTube channel, here: https://youtu.be/SpBItB5nKMQ
Thanks Bruce, fixed that (and it hyperlinks to that page). You are a source of great IFR wisdom! I can’t believe you fly that Bonanza all the way to NH for Pilot Workshops 🙏
Heh, I know, I am an old guy. I like to teach VOR before teaching PBN because once you use PBN going back to VOR is a real challenge. Nothing atrophies like a skill you never really learned in the first place.
A couple years ago I was flying from San Antonio to Sacramento via Albuquerque in my Mooney. I was up at FL200 so definitely IFR even though it was a beautiful day. Normally I would pass south of Area 51 through Las Vegas but this time I decided to go over the N side. Also, GPS was NOTAM’d to possibly be out of service due to testing at White Sands. So I was flying airways to make the transition easier, just in case.
Sure enough, they took down GPS. No big deal as I was already monitoring the VORs. One click and I was using VOR. You should have heard the airliners screaming tho’. Just as I was feeling really pleased with myself I switched from ABQ to GUP … and it was off-the-air.
“Albuquerque Center, Mooney 916BL, uh, I need a vector to Page. Gallup seems to be off the air.”
“Mooney 6BL, turn right heading 295° until receiving Page, then direct Page, rest of route unchanged.”
Tracking a VOR is still a necessary skill that atrophies if you don’t use it. In any case, you gotta be able to use it all, even vectors and DR if it comes down to that, PBN notwithstanding. I have had GPS just go away too many times for me to trust it for all my nav. The underlying VOR network is there for a reason.
Fluency/competence with the VOR system is a tough “sell” in the modern “magic nav” world and since it requires a very different aptitude than “GPS direct.” I have wrestled with this for years and finally have a pretty simple way to teach VOR fluency to newbies in a series of easy steps. But learning VOR well requires your learner to “buy in.” The fact that GPS might totally disappear while you are in the clouds provides a very good “reason why” that convinces most people. We need to be serious about teaching/learning VOR thoroughly so it is a comfortable and available skill in the toolbox.
But there are definite “levels of mastery” using VOR as a sole source of navigation. It is pretty simple to track to/from a station, but the more difficult skill is building that mental model that allows a pilot to know from dialing a few cross radials, where exactly on the map they are; “global orientation.” This is a skill very closely aligned with “situational awareness”(and critical to safety) This skill has become increasingly rare in modern pilots. Unless they can see their location on the magic MFD, they have no clue of their global orientation! Our orientation (position in place and time) sets the whole stage for successful instrument flight; “what is our next fix, which way and how long till then?”
Unfortunately, most modern, technologically dependent IFR pilots are essentially ‘lost in space” without the “GPS magic.” Even at the private pilot level I constantly ask pilots to point physically to “home base” and orient globally. This is a skill that needs to be developed and improved in every pilot. “How long will it take to get there?” “How much fuel?” WIthout the referring to the “GPS magic,” many very good pilots are lost. VOR training and orientation definitely helps with this skill.
Brian, you are spot on sir! This CFI-I now teaches VOR first for instrument flight navigation training before diving into GPS. Once you master VOR navigation and approaches, GPS is like cheating. Also, you can get a GPS error anywhere in the country. I was with a student flying Practice LPV approach (LZU), when suddenly the GPS needles froze even though my student was tracking away from the approach course. Nothing was NOTAM’d but 5 seconds later it started functioning normal. Bottom line is it vital to safety to stay proficient on the old VOR as you never know when you might need it.
AND, the whole MON system (for GPS failure) is dependent upon VOR proficiency to navigate safely out of the clouds; mandatory!