GPS Transition, Part III: Conservation of Complexity

Some folk seem to think that if GPS navigation is simple, then something must be done to make it more ... difficult.  Let's call this the Conservation of Complexity Principal: An area of aviation reaches a level of complexity causing pilots, instructors, examiners, inspectors, and even engineers and designers to feel compelled to maintain or even increase that level of complexity. Simplicity should be a primary goal in systems design and it is unfortunate when we mistake increased complexity for progress. Newer glass panel aircraft have a ton of features, some crucial, some cool, and some seldom-used “gee whiz” features. RNAV procedures and equipment are also cool, they provide much flexibility and increased accuracy, but they are mired in a confusing swamp of details. Here are some thoughts on embracing the essentials while eschewing the geeky.

Can You Top This?

Needless complexity comes into the picture when equipment and procedure designers, probably under time pressure, jump to a quick solution. Some hardware manufacturers, hoping to establish market differentiation, end up designing too many features into their products. Some pilots, instructors and examiners embrace this geeky stuff without any clear evidence that knowing lots of minutiae in any way enhances learning, proficiency, or safety. Requiring pilots to understand and recite facts about the GPS satellite constellation or to describe the Line-Replacable Units that make up the G1000 and how they communicate with one another has few clear advantages, other than making it easy to test a candidate’s knowledge of the nitty-gritty.

It may be interesting to know the model designations of each G1000 component and the network media used to connect them, but what does that have to do with effectively managing the technology in newer aircraft while flying single-pilot? At it's worst, teaching detailed systems knowledge may encourage pilots to try to figure out why something has failed while in flight, resulting in a distraction that can adversely affect the safety of flight. If a GPS or one of its components fails during flight, the pilot needs to recognize the failure and understand the extent to which their ability to navigate has been affected. Then they can get the aircraft safely on the ground and have an avionics tech diagnose and fix the problem. Acquiring and maintaining complex, systems-level knowledge of the G1000 is not needed unless you plan on repairing the hardware yourself.

Papier-mâché Unicorn

RNAV procedures and policies have grown up over time with the added challenge that they be made to exist with existing VOR/NDB procedures and policies. Add a little here, a little there and after a decade you stand back to look at what’s been created. Voila! It’s a unicorn! In defense of the FAA, a tremendous number of new RNAV procedures have been created and the majority of them for other than Part 139 airports (i.e. GA airports). Nevertheless, mistakes were made.

Charting complexities add tiny bits of workload in a single-pilot environment. Approaches have titles like RNAV (GPS) RWY 22, but then there are obscure rules that say any item contained in parenthesis is to be omitted. There are variations and inconsistencies in terminal arrival areas, the depiction of minimum safe altitudes, required equipment, important details buried in notes, and even special climb performance on the missed approach. Trying to keep all of this straight while flying single-pilot may seem like death by a thousand cuts and can contribute to creeping task saturation. Here’s an approach for an airport in my area that was published and then quickly NOTAM’d as not authorized. Hmm ...

Need to Know

GPS units like the G1000 offer a plethora features, leading many pilots to mistakenly believe they need to understand all of the bells and whistles. Many pilots see this morass of details and just turn away. So here’s some heresy for you: You don't need to understand every single feature. It is possible to get along just fine without knowing how to get your GPS to add an along-track-offset or display a parallel track. Once you understand the basic concepts of waypoint navigation, GPS flight plans, automatic waypoint sequencing, turn anticipation, and how to load procedures, you can hone your skills using the concise list of tasks that every pilot should be able to accomplish with their GPS under instrument flight rules, found in the AIM (1-1-19(p)).

1. Perform a RAIM prediction function
2. Insert a DP into the flight plan
3. Program the destination airport
4. Fly an overlay approaches (especially procedure turns and arcs)
5. Change to another approach after selecting an approach
6. Fly "direct" missed approaches
7. Fly "routed" missed approaches
8. Enter, fly, and exit holding patterns
9. Program and fly a "route" from a holding pattern
10. Program and fly an approach with radar vectors to the intermediate segment
11. Handle a RAIM failure both before and after the FAWP
12. Program a radial and distance from a VOR (often used in departure instructions)

Devil in the Details

At the heart of every GPS receiver is a computer running software and as the late John Ciardi said, "Computers are high-speed morons." GPS database designers encode airports using a four-character ICAO identifier and VORs with a three-character identifier. In some cases, the VOR is located on an airport with the same name and identifier, often not far from the surveyed center of the airport. The FAA's charting division needs to clean up their act and use four-character ICAO airport identifiers on their chart products. This one simple change would make everyone’s life easier, but as of this writing the Aeronav folks haven't gotten around to it.

If you fly RNAV approaches with an IFR-certified WAAS GPS, you’ll need to be prepared to fly up to one of three different minima on an approach - LPV, LNAV/VNAV, or LNAV. You also need to correlate the course sensitivity a GPS displays during an RNAV approach to the correct minima shown on the approach chart (LPV = LPV and LNAV/V = LNAV/VNAV). If your GPS is not WAAS capable, you’ll only get LNAV minima and your life is simpler.

This brings up a question that many renter pilots have a hard time answering: How do you know if the plane you just rented has a WAAS GPS or a non-WAAS GPS? There’s nothing on the face of the GPS unit that tells you this, you have to consult the Approved Flight Manual Supplement.

Another way is to bring up the satellite status display and if you see a “D” in one or more of the satellite signal strength histogram bars, the unit is a WAAS GPS. What does the “D” stand for, you ask? “Differential GPS,” another subtle and annoying mental connection you must make. On G1000 models you also see the term SBAS (Satellite-Based Augmentation System) instead of WAAS.

Non-WAAS GPS units detect navigational errors with a process called RAIM (Receiver Autonomous Integrity Monitoring), which is analogous to seeing a flag appear on your VOR course deviation indicator or HSI to indicate the station is unusable. WAAS GPS units use a different error detection process called FDE (Fault Detection and Exclusion), another good reason for knowing exactly what kind of unit resides in the instrument panel of the aircraft you just rented or may be thinking of buying.

Updates to GPS databases are made available every 28 days, database subscriptions are not cheap, and downloading and applying the updates can be time-consuming. These are the costs of doing GPS business and if you fly at night, over remote areas, or in the clouds, you don't want an out-of-date database. Many feel that the costs of database updates has gotten out of control, especially when an aircraft owner must have multiple database subscriptions for the same model of GPS unit installed in the one aircraft. Glass panel aircraft may have numerous other databases, often with differing expiration dates. When the tension between being safe and legal collides with saving time and money, databases don’t get updated and renter pilots need to be prepared. The plane you just rented may have lots of glass in its panel, but if the GPS aeronautical database isn’t updated the plane goes from “/G” to “/U”

Wither ERAM?

Last, but not least, is the FAA’s continuing struggle to provide IFR clearances that take advantage of the capability of the most basic GPS receiver. One of the problems has to do with FAA flight plan formats because there is only so much information about an aircraft’s type of RNAV equipment that can be encoded in a single letter, like “/G.” ICAO flight plans provide much needed detail on just what level of RNAV capability an aircraft does or does not have. ICAO flight plans are now required for aircraft that desire RNAV departures. Even if you don’t file an ICAO flight plan, you can request and get an amended clearance to proceed direct to a waypoint or VOR once you’re airborne, but that means reprogramming a GPS flight plan in flight. Not just occasionally, but every time.

At the crux of this problem is the FAA’s computerized system for generating clearances that hasn’t changed in years. The new ERAM (En Route Automation Modernization) system was supposed to change all that, but it doesn’t seem to be working out very well at the moment. I’ve tried filing all sort of routings out of KOAK using ICAO flight plans with various routing strategies, but I always get the same routings. Having a technically advanced aircraft with all sorts of accurate, flexible navigational capabilities doesn’t count for much if the ATC computers are not prepared to play ball.

The best bet still seems to be using your local knowledge of what ATC usually assigns or use one of the many briefing services (FltPlan.com, ForeFlight, FlightAware.com) that can tell you what routing has recently assigned to your destination. Use that routing on your flight plan and once airborne, start asking and negotiating a more direct routing with the controller. Kasparov may have been beaten by a chess-playing computer, but it seems ATC professionals are still more flexible and creative in the aviation chess game.

Hits Just Keep Coming

Now that you understand the basics of GPS navigation, the features that were supposed to make your piloting tasks easier, you should be better equipped to learn the complexities of your particular model of GPS so you can bend it to your will. Stick with the basics, practice those tasks listed in the AIM, and you should have fewer moments of GPS confusion. You might even find that if you hold you nose, bite your tongue, and cross your fingers you’ll find that GPS navigation is not really all that bad. Eventually one hopes that the FAA and the equipment manufacturers will see the error of their ways, fix the screwed up user interfaces and develop strategies to smooth out the significant RNAV wrinkles (or at least keep more wrinkles from appearing). Until they do, take heart in what Dos Passos observed: There are things that could be more, but are content to be less.

GPS Transition, Part II - Waypoints 'n Stuff

Once you understand how dead reckoning and VOR concepts relate to the world of GPS, you’re ready to move on to waypoint sequencing and turn anticipation. Understanding these two concepts is fundamental to the effective use GPS flight plans, the handling of ATC routing changes, and to reducing the likelihood that you’ll find yourself asking “Why’s it doing that?”


Waypoint Navigation




One goal of RNAV was to simplify navigation from the pilot's point of view and GPS generally offers significant improvements in navigational accuracy and flexibility. Okay, the equipment manufacturers have made things difficult with questionable user interface designs. The FAA and its contractors have created complicated procedures that expose levels of detail that could (and should) be opaque to pilots, but we'll go down that rabbit hole later. For now consider that there are really just two conceptual steps to waypoint navigation: Enter a waypoint into the GPS receiver, then navigate to the waypoint using the desired track and current track provided by the GPS. Don't forget to set your course pointer or OBS to the DTK supplied by the GPS or you'll see a message like the one shown above.


In its most primitive form, waypoint navigation means pressing the GPS receiver's Direct-to button, but you can also enter a sequence of waypoints (aka GPS Flight Plan) and this is where waypoint sequencing and turn anticipation come into play. The mechanics of creating, storing and activating GPS flight plans vary by brand and model of GPS, but for now we’re just talking about concepts.


Shake a Leg


Navigating the desired track (think magnetic course) between two waypoints in your flight plan is referred to as leg flying, which is different from just proceeding to a waypoint from your current position using the direct-to button. Proficiency training with a specific GPS unit should include demonstrating that you understand the difference by proceeding direct to a waypoint as well as activating a flight plan leg, then interceping and flying that leg.

The active leg is usually shown as a magenta line on the moving map whereas previous and subsequent legs to be flown are shown as white lines.

Best Laid Plans


For VFR flying, you can use any waypoints you want in your GPS flight plan; VORs, airway intersections, airports, visual reporting points, or anything else contained in the GPS database. You’ll still want to ensure you're steering clear of restricted airspace, active MOAs, and terrain or weather that might make you wish you were doing something else.


For IFR, your GPS flight plan should ideally match your IFR clearance. This is where the perfect, sequential, tidy world of GPS meets the rough and tumble, real-world of ATC vectors and amended clearances. Start by entering your departure airport and your destination airport. It would be nice if you could enter an alternate airport, but amazingly, most GPS units (save the discontinued G480/CNX80) still don’t support this concept!


IFR clearances may specify a SID (Standard Instrument Departure) or they may specify a heading to fly until ATC vectors you to join the en route structure. Most IFR-certified GPS allow you to load a SID based on your departure airport (the first airport in your flight plan). If the SID has more than one transition to the en route structure, the GPS will prompt you to specify the transition that ATC assigned. Loading a SID often requires you specify the departure runway and this can be especially critical for RNAV SIDs. Loading a SID will insert all the necessary waypoints into your flight plan.

Some SIDs are pilot-nav, the theory being that you fly the procedure with minimal input and guidance from ATC. Other SIDs are vectored, with the assumption that ATC will guide you to the en route structure. Many older GPS units don’t provide a way to load a vectored SID, so just enter the waypoint (usually a VOR) that defines the transition to which ATC is going to guide you. Either way, it's not uncommon for ATC to assign you headings to fly in order to separate air traffic, eventually telling you something like “when able, resume the Wild Goose Chase departure ...” This is where activating the appropriate leg from your GPS flight plan is a need-to-know skill.


Anytime you are being vectored, the heading you are flying may not correspond to the magenta line that the GPS is depicting. This often causes concern for an RNAV tenderfoot, but remember that the compass and heading indicator are also IFR instruments and you won’t always be following the GPS’s magic, magenta line.


Defining Victor or Jet Airways for the en route portion of a GPS flight plan is fairly straightforward: Just enter the name of each VOR and any changeover points in between. Some newer GPS units provide a way to load an airway and will fill in the necessary waypoints for you, but the process can be convoluted. The idea is you start with a waypoint on the airway that ATC has assigned, then select the airway you want to load from a list of possibilities, and then specify where you want to get off the airway. This will add the necessary waypoints to your GPS flight plan.


Loading a STAR (Standard Terminal ARrival) or IAP (Instrument Approach Procedure) for your destination will require you to specify the transition (where you want to enter the procedure). Loading these procedures will add waypoints to your flight plan. And like a SID, you may get vectored around by ATC and you’ll need to know how to proceed direct to a waypoint or how to activate and join a leg of the procedure.


So a GPS flight plan is just a collection of waypoints that you either entered yourself or that were added when you loaded a departure, arrival, or approach procedure. If all goes as planned, you’ll fly to each of those waypoints in a nice, orderly sequence. Scratch that. Things never go as planned, so you need to know how to find your way through the flight plan and navigate direct to a waypoint or how to activate a leg.


Fly-Over vs. Fly-By


Now that you know (at least a bit) about GPS flight plans, let’s revisit waypoint sequencing. GPS keeps track of where you are and as you reach the current waypoint, it usually sequences to the next waypoint, calculating the new desired track, distance, time en route and other stuff in the process. Yet there are times when a GPS won’t automatically sequence to the next waypoint and it’s important to understand the when and why this will occur.

The majority of the waypoints in your GPS flight plan are called fly-by waypoints, usually depicted on charts as a four-pointed star. As the name implies, you don’t have to fly directly over these waypoints. Since the GPS knows your groundspeed, current track, and the number of degrees of change between the current DTK and the upcoming DTK, it can provide turn anticipation for fly-by waypoints. If you pay attention, follow the GPS’s advance warning and turn when it says to turn, you’ll end up on the new DTK. Old school pilots who were taught to fly past a VOR, verify station passage, then turn to the new course may find they have trouble letting go of their old habits. Just keep reminding yourself that turn anticipation is a good thing.

Another type of waypoint is called fly-over. As the name implies, you must fly right over a fly-over waypoint. Try as I might, I couldn't find a definition of just how close you must pass to a fly-over waypoint but my personal experience is that it's pretty damn close. One example of a fly-over waypoint is the missed approach waypoint on an IAP: Fly over the MAP and you’ll have to push a button to re-enable waypoint sequencing to the missed approach segment (on most GPS units). Same holds true for most missed approach holding waypoints. Which button you push to re-enable waypoint sequencing depends on the brand and model of GPS.


Some RNAV SIDs and STARs have fly-over waypoints, depicted as a four-pointed star enclosed in a circle, but waypoint sequencing is not suspended for these waypoints on a SID or STAR; The procedure designers just want you to navigate to these waypoints very precisely.

You can manually suspend waypoint sequencing for any waypoint at any time by pressing a button. Depending on the brand of GPS receiver you're using, the name of the button or softkey may be OBS or it may be SUSP, but press that button or softkey and the GPS won't sequence from the current waypoint until you intervene with another button push: Pretty handy when ATC tells you to fly an ad hoc holding pattern using the current waypoint as the holding fix.


Many pilots ask why some GPS receivers call this feature OBS and I the reason is that pressing that button lets you treat the current waypoint as though it were an old-fashioned VOR: You can turn your course selector or OBS knob and set whatever DTK to the waypoint you want. When you press OBS or SUSP, you’ll see a magenta line on your moving map leading to the waypoint on your selected DTK and a white course line extending outward on the opposite side of the waypoint.


Missed Opportunities


GPS receivers allow pilots to load all sorts of instrument approaches, thereby adding the necessary waypoints that make up the approach to the GPS flight plan. Monitoring a moving map to maintain situational awareness during an approach is cool, but the waypoint sequencing get's messed up when you are being vectored to intercept the approach. When being vectored, the first task is to activated the correct leg of the approach so that the GPS will sequence through the waypoints in your flight plan in the correct order as you fly the approach. For a detailed discussion of this issue with Garmin units, go here.


Lastly, consider the location of the missed approach fly-over waypoint (MAP) for an ILS or an RNAV approach with vertical guidance (LPV or LNAV/VNAV). For approaches with vertical guidance, the MAP waypoint is defined by centered localizer/LNAV and glide slope/VNAV needles at the Decision Height (DH). Consider also that the FAA puts ILS and localizer-only approaches on a single approach chart as it does for RNAV LPV and LNAV/VNAV approaches. GPS designers had figure out how to handle this and they came up with this kludge: They consider the MAP waypoint to be at the runway threshold. The MAP waypoint is given a name like RW34 for “runway 34.”

In the example above, you reach the DH, see nothing but clag, and start the missed approach. The GPS will not have yet suspended waypoint sequencing since you haven’t arrived at the runway threshold, so you’ll need to fly over the runway threshold before you can activate the missed approach. Oddly, the Garmin G1000 provides an Activate Missed Approach feature, but every time I’ve tried to access that feature it had a grayed-out appearance and couldn't be selected.


Stay Ahead, Keep Ahead


Now you know a bit more about the crucial foundations of RNAV: The importance of automatic waypoint sequencing, the role of a GPS flight plan, how your GPS flight plan may not conform to the real world, and the important difference between direct-to and leg navigation. You've probably noticed that we're delving into increasingly complex RNAV concepts, so stay tuned for my next installment: Creeping RNAV complexity and what you can do to combat it.

Something Can Be Done

The promise of Area Navigation (RNAV and GPS) was that it would be a simpler and more accurate way to navigate than older styles of navigation and to a great extent, that promise has been realized. GPS accuracy, especially when augmented with WAAS, is very good indeed. As for simplicity ... not so much. Waypoint navigation was a revolutionary concept when it was introduced, but it has been integrated with existing navigational paradigms and infrastructure in an evolutionary manner, not unlike the way an artist might sculpt clay or mold papier-mâché. This evolutionary approach has created some unfortunate and unforeseen complexity, but it doesn't need to be that way. Mom always said "Don't complain unless you can offer a solution or a suggestion," so here are my top five recommendations for simplifying the world of RNAV.

Wayward Waypoints


Many airports out there have a VOR located at airport and in those cases the VOR and the airport have the same name. Just as often the VOR may be some miles away from the airport, but both still have the same name. At the heart of every GPS receiver is a computer running software and software doesn't tend to handle ambiguity very well. That's why the GPS database encodes airports using a four-character ICAO identifier and VORs with a three-character identifier. The FAA's charting division could do us a big favor by using four-character ICAO airport identifiers on their chart products, but they don't. If they did, it would be crystal clear to student pilots and budding instrument pilots that KSAC refers to the surveyed center of the Sacramento Executive airport while SAC refers to the Sacramento VOR. 

Not in Kansas Anymore

The first step in GPS navigation is to enter the name of a VOR or NDB station on the ground, the name of an intersection of two VOR radials, an airport ID (which represents the surveyed center of the airport), a charted VFR reporting point, a Computer Navigation Fix defined by FAA chart designers, or even a user waypoint that you've created. The AIM refers to this type of navigation as to-to, not to be confused with Toto, the little black terrier in the Wizard of Oz. GPS receivers only navigate to one waypoint at a time, also known as the current waypoint.

GPS makes it simple to navigate to a waypoint and most receivers provide a moving map display, which is a score for simplicity and safety. The bad news is that unless you're lucky enough to have a keyboard as part of your GPS receiver, entering a waypoint requires a precise and often convoluted sequence of knob-turning and button-pushing. A bad user interface makes it all too easy to misspell the name of the waypoint: Get just one letter wrong and instead of navigating to a VOR that is 20 miles away, you may be headed to Tierra del Fuego by mistake!

The engineers that designed GPS receiver user interfaces didn't set out to create difficult-to-use products, but the fact is they did. Whether it was the desire to save a few bucks by having fewer knobs and buttons or simply a race to get a product to market, it's clear that mistakes were made. Now the users of these products have to live with the mistakes and to quote Warren Zevon, "… it ain't that pretty at all." Bad UI design is the Achilles heel of GPS and many of us pilots have become so acclimated to these convoluted interfaces that we have lost sight of just how whacked this situation is.

Near the top of my "need to fix" list is Garmin's Small-Knob/Big-Knob interface. You press the small knob to enter "cursor mode" so you can edit or enter the name of a waypoint in a flight plan. You turn the small knob to start the process of entering letters and then the small knob changes function. Whoa there! A knob whose function changes depending on an interface context that is mostly invisible to the user? This needs to be fixed and one simple way would be a separate button dedicated to starting and ending the waypoint editing mode.

Having a separate button for edit mode would also fix the problem that countless new Garmin users run into: Pressing the small knob to exit cursor mode and accept whatever changes they have made. Having watched hundreds of pilots make this mistake thousands of times it's clear that a common intuitive belief is that if you press one button or key to enter a mode, pressing the same button or key should exit that mode. In the Garmin world, this simply exits the editing mode and, here's the amazing part, destroys whatever changes you made without asking you to confirm that's what you want to do. This is B-A-D.

Missing Pieces on the Missed Approach

When flying an instrument approach, most GPS receiver are designed to suspend the automatic sequencing of waypoints when you reach the missed approach point. Think about this for a moment: You're close to the ground with reduced obstruction clearance at a high-workload moment. You're either going to see the runway and land or you won't see anything and you'll fly the missed approach. Is this really the time to make a pilot divert their attention from controlling the aircraft to push the OBS button or SUSP soft-key? I don't think so and apparently neither did the designers of the GNS 480 (nee CNX 80), which will automatically sequence to the missed approach segment. If you see the runway environment and decide to land, you just ignore the GPS. If you don't see the runway environment or loose sight of the runway while circling, use the GPS to start navigating on the missed approach. Too bad the GNS 480 is out of production and the GPS units that are in production don't exhibit this behavior. A defense I've often heard is that the TSO specifies that pilot action is required to initiate the missed approach and if this is true, the TSO should be changed.

When flying a non-RNAV approach, many GPS receivers automatically switch the navigation source from GPS to the VOR or localizer receiver. That's great, but if you need to fly the missed approach and you want to use the GPS to do so you must divert your attention and manually select GPS as the navigation source. I mean really! If it's okay to automatically switch navigation source out of GPS, why not back into GPS mode?

Four Card Minima

There's a new game for RNAV approaches that all pilots must play and it's called "Guess the approach minima." It goes something like this. When you brief an RNAV approach, you may see up to four sets of minima listed: LNAV, LNAV/VNAV, LPV and circling. The issue is you may not know which minima your WAAS GPS receiver can offer (based on current signal integrity) until a few miles before the final approach fix. This has to do with the design of WAAS GPS receivers' final signal integrity check and I honestly can't think of a good way around this shortcoming: You just have to brief multiple approach minima and choose the correct minima based on the approach sensitivity your WAAS GPS receiver displays.

Where improvement could be made would be to ensure that the approach sensitivity displayed on the GPS receiver exactly corresponds to the approach minima shown on the chart. If your receiver arms with  LPV or LP sensitivity, you're okay because your WAAS GPS receiver should display LPV or LP. If the receiver arms with LNAV sensitivity, you may see LNAV or LNAV+V. If it arms with LNAV/VNAV you'll probably see LNAV/V. Notice the subtle, similar appearance of LNAV+V and L/VNAV? This is too subtle and is B-A-D. And the minima shown on the charts should exactly match the minima displayed on the GPS receiver, period, end of discussion.

Procedure Turn or No?

The introduction of the Terminal Arrival Area (or TAA) was meant to simplify pilot/controller interaction when executing an RNAV approach. And it would be simpler, were in not for the fact that not all RNAV approach charts follow the same conventions with regard to the depiction of a hold-in-lieu-of procedure turn (or HILO). In particular, some RNAV approaches have a standard Minimum Safe Altitude circle while others display minimum safe altitudes in sectors on the plan view of the chart. The subtle problem is that MSA sectors will usually tell the pilot that the procedure turn is not authorized when you're headed straight-in to an Initial Approach Fix where a HILO is depicted, while approaches with the MSA circle do not.

If you were approaching from the Southeast and were told "when able, proceed direct HERMIT, cleared RNAV 34 approach" you need to read the fine print on the MSA sector shown on the plan view to know when you could descend and to know that the HILO is not authorized.

If you were told "when able proceed direct CADAB, cleared RNAV 29 approach," you need to know that the hold-in-lieu-of procedure turn is required unless the the controller remembers to say "… cleared straight-in RNAV 29 approach."

The FAA charting division needs to come up with a consistent way of depicting MSA and clearly denoting when a procedure turn is required and when it isn't. Until then, pilots should ask the controller when they see a HILO and they aren't sure whether or not they are expected to fly the procedure turn.

More Fond Wishes

So that's my wish list of the top five features and enhancements I'd like to see for the world of RNAV. You may have your own list of desired features, too. For now, we can only hope that the people in a position to fix these issues are listening.

Understanding RNAV approaches

While perusing the searches people use to find my blog, I often notice that many are looking for information on RNAV approaches. My earlier posts on this topic were done using examples from a PC simulator when LPV approaches were first becoming available. Now that the number of LPV approaches outnumber the ILS approaches available and I've flown hundreds of different RNAV approaches, it's clearly time to revisit this complex and popular topic. So here's practical information on RNAV approach design, naming conventions, the different approach minima that you might encounter, the types of vertical guidance that may be offered, how ATC will get you established on the approach, and some pre-flight planning considerations.

Tomaeto, Tomahto

RNAV stands for aRea NAVigation and encompasses a variety of aircraft equipment described in U.S Terminal and En Route Area Navigation (RNAV) Operations. Appropriately certified GPS units are considered RNAV as are many Flight Management Systems. Older VOR/DME RNAV units are also consider RNAV units, but in a much more limited way. In simplest terms, an IFR-certified GPS unit is most often the straw that stirs the RNAV drink for most GA aircraft.

For RNAV-equipped aircraft, it's easy for a pilot to navigate directly to a VOR, NDB, intersection, or approach waypoint. That's why RNAV approaches are often designed with a Terminal Arrival Area or TAA (not to be confused with a Technically-Advanced Aircraft). The TAA is a T-, Y- or L-shaped arrangement of Initial Approach waypoints designed to simplify the interaction between ATC and the pilot. A good, detailed description can be found in the Aeronautical Information Manual section 5-4-5(d).


What's in a Name?

Any approach title items contained in parenthesis are omitted when referring to the approach, so both the pilot and ATC would refer to the approach shown below as the "RNAV Runway 12 approach" - GPS is left out because it appears in parenthesis. A stand-alone GPS approach, like the Rio Vista GPS RWY 25 approach would be called a GPS approach. Confusing? Yeah, but supposedly all GPS approaches are eventually going to be renamed to RNAV approaches, it will just take some time.

If you desire an RNAV approach, think like a controller and include your approach request when you check in. Controllers usually appreciate this as it is unambiguous and it saves time.

Santa Barbara approach, Barnburner 123, 7000, request Santa Maria RNAV 12, direct WINCH, with information Foxtrot.

Some RNAV approaches contain "RNP" in parenthesis, which stands for Required Navigational Performance. These SAAAR (Special Aircraft & Aircrew Authorization Required) approaches are not available to us mere mortals.

Some RNAV approaches contain the letter Z or Y and the reason is simple: FMS databases can't handle two approaches to the same runway using the same navigational system, so the letters Z or Y are added to prevent ambiguity. Some kludge, eh? The deal is this: RNAV Z approaches usually provide lower approach minima (typically LPV) than RNAV Y (typically LNAV and LNAV/VNAV) approaches, but sometimes the opposite is true. More on approach minima later.

So what approaches can you fly with an old VOR/DME RNAV unit like the venerable King KNS80? The only RNAV approaches you can fly with these units are the ones named
"VOR/DME RNAV ..." There are 60 to 70 of these approaches in the US, like the UKI VOR/DME RNAV or GPS-B approach. Someone could write a master's thesis on the details behind the naming of that approach!

Cleared Direct ...

A controller will typically clear you to the nearest IAF and then provide an approach clearance. The pilot loads the RNAV approach with the IAF transition specified by the controller, activates the approach, and then follows the guidance to each of the waypoints in the sequence that make up the approach. Consider the Santa Maria RNAV (GPS) RWY 12 approach.



There are three IAFs: OVMAF, WINCH, and LILWU. ATC will usually clear you to the IAF nearest to your position. If you are approaching from the Southeast, "direct WINCH" would be a safe bet and you'd need to fly the HILO (hold in-lieu of a procedure turn) to reverse course. The transitions from OVMAF and LILWU all say "No PT" and you should not fly the HILO without ATC's permission (see 14 CFR 91.175(j) Limitation on Procedure Turns).

Many pilots I've spoken to are confused by TAAs that have a 90 degree turn from the Initial Approach segment to the Intermediate Approach segment. Relax because GPS units provide turn anticipation and the TAA waypoints are fly-by waypoints (you're not required fly right over them). The GPS knows your ground speed, actual track, and the number of degrees of turn required, so just pay attention to your GPS, start the turn when it tells you to turn, and you should end up right on intermediate approach course.

*** Edited 4/22/09, based on NTC comments ***

What about the Vectors-To-Final option for loading an approach? Use it with caution because ATC is restricted from clearing you direct to any waypoint inside the Intermediate Fix (IF) or vectoring you any closer than 3 miles from the FAF on an RNAV approach. Not that this hasn't stopped some controllers from doing otherwise. Vectors-To-Final will only display the the FAF and MAP and I'm not sure why Garmin units even provide you this option for RNAV approaches. I guess it could be useful in an emergency, but not in normal operations.

***

Many GPS units also contain VOR receivers so ensure that your HSI or CDI is displaying the GPS course. Otherwise you might get confused when the course doesn't come alive and ATC starts asking you what the heck you are doing.

When to Descend?

The Santa Maria RNAV (GPS) RWY 12 approach depicts the Minimum Safe Altitude in sectors based on the waypoints WINCH and LIWLU, but many RNAV approaches have a conventional MSA depiction. Nice of the FAA to keep it simple, eh? You reference the MSA altitudes like the one depicted on the Santa Maria approach once you're cleared for the approach without any altitude restriction from ATC.

Let's say you're approaching from the Northwest and Santa Barbara approach clears you direct WINCH. You load the approach with WINCH as the transition and activate the approach. Your GPS may then ask you if you want to load the hold and you say ... wait for it ... NO!

Your GPS says the desired track to WINCH is 142 degrees and ATC clears you for the approach. You are at 7000 feet and 9 miles from WINCH, so you can descend to 5500 feet. Once you are within 6 miles of WINCH, you can descend to 3300 feet. Passing WINCH, follow the altitudes listed on the profile view of the approach chart. Simple, once you understand the conventions.

The "How Low?" Lowdown

RNAV approach charts may have as many as four different types of approach minima (ceiling and visibility) and this is probably the thing than confuses most pilots who are new to RNAV approaches. The possible minima are labeled:

• LNAV - lateral navigation only, no descent guidance
• LNAV/VNAV - lateral navigation with advisory descent guidance
• LPV - Localizer Performance with Vertical guidance
• CIRCLING - when straight-in minima are not published or circling is desired.

If your GPS is non-WAAS (TSO C129), then life is pretty simple: You only get LNAV minima and you fly the approach like any other non-precision approach, descending as indicated on the profile view of the approach chart. A good practice is to perform a RAIM check on a TSO C129 unit prior to departure and again prior to reaching the IAF.

If you have a WAAS GPS unit (TSO C145 or 146) you can skip the RAIM check, but you should check for WAAS outage NOTAMs for your destination as part of your preflight briefing. With a WAAS unit, the approach chart minima you will use will depend on the course sensitivity the GPS unit displays when your are flying the approach, a few miles outside the FAF. This course sensitivity depends on the WAAS signal integrity and may vary from day to day and hour to hour.

When you activate the approach, your WAAS unit will probably display TERM sensitivity - a full-scale deflection of the course needle (left or right) represents a 1 mile displacement (left or right) from the desired track.



Somewhere before the FAF, usually at the last intermediate fix before the FAF, the sensitivity will change to either LNAV, LNAV+V, L/VNAV, or LPV. (Some approaches list GLS minima as N/A, but this is just a placeholder, it will be replaced eventually with LPV.)

LNAV+V, L/VNAV, or LPV course sensitivities all offer basically a 0.3 mile full-scale deviation and they also provide vertical guidance, but there are crucial differences between the type of vertical guidance provided.

Anytime vertical guidance is provided, be aware that the glidepath may be provided all the way to the surface. Therefore the pilot must ensure they (or the autopilot) do not descend below the MDA or DA appropriate for the course sensitivity displayed by their GPS unless the appropriate visual references described in 14 CFR 91.175 are present.

Advisory Guidance

LNAV+V provides only advisory guidance and this is considered a non-precision approach: You need to ensure you do not descend below any step-down altitude listed on the approach chart's profile view. You may see LNAV+V on some RNAV approach charts that only have LNAV minima, but you may also see it on an RNAV approach where the required signal integrity for LPV is unavailable. RNAV approaches with only circling minima and with an approach course that is more than 30 degrees out of alignment with any runway will not display advisory guidance. The advisory vertical guidance should be a constant glide angle required to get you to MDA a bit before the missed approach point. If you are an adherent to the "dive and drive" style of non-precision approach flying (I am not, by the way), then you can ignore the advisory guidance all together and fly a less-than-stabilized approach.

L/VNAV

This sensitivity is Garmin's way of telling you that this is an Approach with Vertical Guidance (APV): If you follow the glidepath and the lateral guidance to the Decision Altitude, you won't hit anything. I suspect Garmin chose L/VNAV because 1) they didn't have enough characters available to display LNAV/VNAV and 2) they wanted it to be distinguishable from LNAV/+V. Find that confusing? You're not alone!

L/VNAV vertical guidance is provided all the way to the surface. Therefore the pilot must ensure they (or the autopilot) do not descend below the DA unless the appropriate visual references described in 14 CFR 91.175 are present.

LPV

This sensitivity is also to a Decision Altitude and is considered an Approach with Vertical Guidance (APV). The LPV approach provides lateral and vertical guidance similar to an ILS, but usually to a DA no lower than 250 HAT and no less than 1/2 mile visibility.

LPV sensitivity will be annunciated at the last fix before the final approach fix. On the Oakland RNAV (GPS) RWY 27L, this is also where the glidepath will begin being displayed on most GPS units. Interestingly, glidepath intercept is depicted on this chart's profile view at the FAF. For an ILS, the makes sense because of the physical construction and limitations of the ILS. RNAV glidepaths don't have these limitations, so I don't see any risk in following the LPV glidepath as soon as it appears. Just verify your altitudes at each waypoint.

Glidepath to Where?

Pilots have asked me if the glidepath provided for L/VNAV or LPV approaches, like an ILS glideslope, would take them to the touchdown zone. I'm not certain, but my understanding is that the glidepath (or glideslope) for CAT I approaches takes the aircraft to a Threshold Crossing Height (TCH). Look at any RNAV approach chart that provides LNAV/VNAV or LPV minima and you should find that a glideslope angle and TCH are listed, just as you'd find for an ILS.

In order to Serve you Better

If you see an error message saying that the GPS is unusable while flying an RNAV approach and still outside the FAF, you need to execute the missed approach. If this happens inside the FAF, the regulations say you can continue the approach. The only way I'd continue is if I already had the required visual references or some sort of emergency.

When planning to fly an RNAV Z approach, you'd best have the RNAV Y version of the approach handy, too. If the required WAAS signal integrity is not available, your GPS may inform you that the approach has been downgraded and that you should use the LNAV minima - those minima won't be shown on your RNAV Y approach chart, but on the RNAV Z approach chart. Nice curveball, huh?

Absence Makes the Pilot Go Missed

You loaded and activated the approach correctly, you identified the correct minima to use, you got to the MDA or DA and you don't see the required visual references. It's time for the missed approach and all IFR-certified GPS units (except older GNS480) will suspend waypoint sequencing at the MAP. You'll need to press a button (and perhaps set a new desired track on your CDI) to start navigating on the missed approach segment. For most Garmin units, you press the OBS button or softkey. For many King units, you press the Direct button.

Too Complex?

Many a pilot has complained to me that RNAV approaches are just too complex. I agree. I think the approach designers and the RNAV avionics designers have created their own treehouse with some pretty complex rules, dependencies, and exceptions. The pilot guides for these products try to describe these operational subtleties, but this is some complex @#%& for single-pilot IFR.

If you've made it this far, congratulations: It's a rare instrument pilot who can stomach this much minutiae. If there's something I forgot to cover, email me or post a comment. And lastly, this post took a fair amount of time to craft. If you found it useful, please click on the donate button on the upper right corner of this page. The amount you donate is up to you, but every little bit helps.

New Advanced Avionics Handbook

For many years it seemed that the FAA's handbooks on aircraft flying, aeronautical knowledge, instrument flying, and weather were hopelessly outdated. Yet in the last two years there have been several updates to these publications that included new graphics and information on the latest equipment, theory, and sources of weather data. All of these books are available in PDF format at no charge, which helps reduce the cost of learning to fly or earning an instrument rating.

One of the books that caught my eye when it first came out was the FAA's Instrument Procedures Handbook. This completely new publication provided much needed information on ATC procedures, instrument approaches, and other stuff that was missing or inappropriate for inclusion in the Instrument Flying Handbook.

The latest new release from the FAA is the Advanced Avionics Handbook, which provides a lot of good conceptual information on the use of GPS and RNAV. This book does not depend on any particular brand of GPS or glass cockpit, which makes it great introduction to pilots who are considering or curious about glass cockpit or GPS training. This book touches on GPS and RNAV procedures, pitfalls, and recommended practices in a way that is independent of the model of GPS, PFD, or MFD that you might use.

While this book is not a substitute for thorough training in the use of your particular brand of avionics, it's a great way to get a leg up on transitioning to a glass cockpit or to a GPS-equipped aircraft. Even if you are experienced in using advanced avionics you should find this book contains good advice and explanations on pitfalls and common errors.

And did I mention you can download it for free? I think I did ...

Approach Planning

The morning fog and stratus pulled back to the center of Monterey Bay, there were only few aircraft in the area, and that gave me time to ponder all the flights I made through this area in my freight hauling days. It brought back a lot of memories - some good, some not so good. But we weren't hauling freight. Our purpose was to provide a little variety during instrument training by mixing some VFR flying across San Francisco Bay with a couple of instrument approaches into Watsonville.

There was initial confusion on the part of a ground controller who sounded like one of many new arrivals to Oakland's North Tower. We'd briefed the VFR transition over the San Mateo Bridge mid-span prior to starting the engine. The briefing included the transition from Oakland's North Field over the South Field, the importance of staying well clear of San Francisco's Class B surface area as well as underneath the overlying Class B, and the existence of a defined VFR waypoint (VPMID) for the San Mateo Bridge mid-span. I'd said to plan for an initial altitude restriction of 1400 feet, but the new ground controller (who was also working tower) gave us a 2000 foot restriction. When handed off to the South Tower at 900 feet, the South Tower controller (a seasoned veteran) queried "Were you given an altitude restriction?" When we told her 2000 feet, she corrected that to 1400 feet.

A few minutes later, we were handed off to the first of several Norcal sectors and were gradually allowed to climb higher as we motored over the Sunken Ship, past Palo Alto and over Moffett Federal Air Field (a former Naval Air Station). A few minutes later, the Lexington Reservoir was beneath us and a bit later, just clear of the Santa Cruz Mountains, we began the descent just to the east of Capitola.



My student had told Norcal that we were "direct NALLS for a practice Localizer 2 approach into Watsonville, with the one-minute weather." The plan was to do the procedure turn on our own navigation, fly the approach to as close to minima as the VFR traffic at Watsonville would allow, then fly the published missed approach and hold over Salinas (a holding pattern I know all too well). After the holding pattern, we planned to fly the GPS A approach because it offers a DME arc and there are precious few of those in Northern California that are also close to the Bay Area.



As we were outbound in the procedure turn, I remembered why the LOC RWY 2 approach sets off my spidey senses: We were beyond gliding distance from the shoreline, over waters frequented by great white sharks, in a single-engine piston aircraft. So I distracted myself by looking for traffic and pondering the other instrument approaches into Watsonville.



If the coastal stratus has blown in, the Localizer RWY 2 approach may be your only real hope of getting into Watsonville because it is the only approach that will probably get you below the clouds - 680' MSL. There is an NDB or GPS B approach that is lined up with runway 2 that gets you almost as low as the Localizer approach - 900' MSL. The VOR/DME or GPS A approach from the southeast that only gets you down to 1300 feet, which is often just above the tops of the stratus layer.



When flying an aircraft with a WAAS-enabled GPS receiver, the WVI GPS B approach is in some ways more attractive than the Localizer RWY 2 approach. One reason is that the G1000 will provide you with a vertical track on the GPS B approach down to the final approach fix (FAF). After the FAF there's no descent guidance on the GPS B, but you don't get any descent guidance whatsoever with the localizer approach. The other advantage of the GPS B approach is you needn't end up as far out to sea when you make your procedure turn as you probably will with the LOC RWY 2 approach.



There are probably many other cases where a RNAV (or GPS) approach gets you lower or offers advantages over a localizer approach - South Lake Tahoe comes to mind. So when you are considering which approach to fly into an airport, don't forget to examine all your options. The advantages of one approach over another is not always as simple as it seems.

G1000 Wishlist

Having spent several hundreds of hours providing instruction in G1000-equipped aircraft, I've identified some enhancements that could really improve the unit's usability. Some of the features (or were they bugs?) that I've mentioned in earlier posts have actually been addressed by Garmin in software upgrades. I'm not taking credit for inspiring these fixes, but maybe Garmin is listening? With that in mind ...

Disappearing Flight Plan Screen
In a recent software upgrade, Garmin fixed the G1000 behavior of jumping to the end of the flight plan any time you entered cursor mode on the Primary Flight Display (PFD) with the flight plan inset window. It's soooo nice to have it fixed. Now they need to fix the problem of the disappearing flight plan window.

Here's the setup. ATC tells you "When able, proceed direct Linden," so you press the FPL button and scroll with the big knob to select LIN.



Next, you press DIRECT.



Press ENT two times to confirm and you're in business. Unfortunately, the very act of proceeding direct to a waypoint makes the inset flight plan window disappear.



You can press FPL again, but why should you have to?



Hidden Baro Minima
In new G1000 units, you can set the minimum descent altitude or decision height for your approach. When you reach that altitude, you'll hear an aural annunciation "Minimums, Minimums!" (sic). This is a very cool feature, but guess where you access this feature? Press the TMR/REF (timer/reference) softkey and you'll see this inset window.


The TMR/REF window is quite the catch-all because this is where you can change the V-Speeds that are bugged on the speed tape, access a count-up timer, and set the minimum descent altitude. Forget for a moment that changing the bugged V-speed in most light GA aircraft is stupid. How is a pilot supposed to know that he or she can set their minimum descent altitude with this softkey? You need to memorize and remember it's location. If your minimum descent altitude is several thousand feet (like at South Lake Tahoe), you're going to have to twirl that little knob quite a bit to dial in the desired altitude. Actually, the altitude setting is probably optimized for the most frequently occurring altitudes and isn't so bad. Some of the other G1000 altitude inputs make you select one digit at a time, starting with tens of thousands of feet.

Inset Window Amnesia
A related behavior with all the PFD inset windows is that the G1000 does not remember what you were last doing. Press the FPL button to display your flight plan. Then press the TMR/REF softkey to set your Baro Minima. Press the TMR/REF softkey again to dismiss that inset window and ... voila! Instead of displaying the flight plan inset window, there's no inset window displayed at all. The same thing happens if you press NRST, PROC, MENU or any button that displays an inset window. Being able to preserve the last window (or windows) should be child's play for programmers who understand linked lists and the basic concept of LIFO.

XPDR Code, Where Art Thou?

A frequent occurrence when calling ATC to get into the system is being told "Standby for a transponder code." So you press XPDR softkey, the CODE softkey, and wait, ready to punch in the four-digit code.


The problem is that after a few seconds, the G1000 assumes you're done and helpfully dumps you out of the transponder code mode. Gee, thanks ...

Reversionary Mode

As an instructor, I use the reversionary mode a fair amount to simulate the failure of one of the displays for training - the equivalent of partial panel in a steam gauge aircraft. To do this, you press the RED button at the bottom of the audio panel to make both screens display the same basic data - Attitude, Speed, Altitude, engine gauges, and so on. Then press the MENU key and the fun begins.

Using the big knob, you select the brightness setting for the display you wish to make dark and change it from AUTO to MANUAL. Then you select the percentage brightness field and twist the small knob to lower that value to 0%. You must twist, and twist, and twist, and twist, because one complete revolution of the small knob reduces the brightness only about 5%. I'm certain that one day that knob will come off in my hand or just quit working altogether.

One solution would be to have three basic settings: AUTO, MANUAL, OFF. Without some improvement in this interface, Garmin will eventually get sued by some enterprising instructor claiming the G1000 caused repetitive strain injury to their wrist!

Nav Source Change
This is a biggie. The G1000 will automatically (and silently) change navigation source for the HSI (and consequently the autopilot) from GPS to Nav 1 when a ILS approach is loaded. This behavior is generally a good thing, but with the Cessna 172's KAP 140 autopilot in NAV mode, it can be treacherous.

If the KAP 140 autopilot senses the NAV source has been changed, it reverts to the wings level, ROL mode. There's no beep, no chime, no aural alert of any kind. The KAP 140 just flashes ROL for several seconds on the autopilot control panel, but that panel is too low and out of the pilot's primary field of view to be of much help. If the pilot doesn't catch what has happened, the autopilot might just fly him or her into oblivion. One fix for this would be for the G1000 to provide an aural warning "Nav source change" or some other helpful phrase.

Of course, aural alerts can be distracting. A pilot I fly with showed me how to enable aural alerts on an older Garmin GNS480 unit. Unbeknownst to me, this unit was set to a female voice and as I was turning final I heard a very sultry voice say "Five hundred." For a second, all I could think was "Tell me more!"