From the “you learn something every day” file comes a fascinating Air Safety Foundation quiz on RNAV approaches.

For the non-pilots and/or non-instrument rated among us, RNAV is short for “random area navigation” and for the most part refers to satellite navigation — in other words, GPS. It’s not called GPS because there are other area navigation methods such as loran, omega, inertial navigation, and so on.

But they all do the same basic thing, which is to allow a pilot to fly from any random point in the world to any other point. Prior to RNAV, radio navigation consisted of flying from one ground-based station to another. A highway in the sky, if you will, but one firmly tied to the ground. These ground-based stations are housed in little buildings scattered around the country which transmit signals the aircraft’s navigation receiver can follow. The problem is, these buildings are not movable. They’re expensive to build, maintain, and monitor.

With RNAV, pilots can create virtual waypoints anywhere. RNAV systems therefore have more capability than the older ground-based navaids. If you’ve ever used a GPS, then you’re part of the RNAV revolution.

Of course, there has to be a down-side, right? Nothing is free in aviation, and so it is with RNAV. RNAV systems tend to be computerized and therefore more complex. They also tend to fly in the face of thing we’ve learned about IFR navigation. Curving approach paths, precision approaches without an ILS, etc.

For example, every instrument-rated pilot knows that in order to proceed below the published minimums for an Instrument Approach Procedure, three criteria must be met. In general terms, they are:

1. The flight visibility must meet the published minimums for that procedure
2. The aircraft must be in a position from which the pilot can make a normal landing using normal rates of descent
3. The runway environment (pavement, lights, paint, etc) must be in sight

Aside from an esoteric 100′ rule dealing with a specific part of the approach lighting system, there are no exceptions. Or at least, that’s what I thought until the RNAV quiz taught me about “fly visual” segments.

“Fly visual” segments are typically seen on approaches to airports in mountainous areas. Treat them as red flags: If you see one, take some extra time and give the procedure a closer look.

There are a couple of reasons for this. First, as discussed in the main portion of the course, the visibility required for the approach is sometimes less than the length of the “fly visual” segment-meaning that the pilot can legally continue beyond the DA/MAP without the runway environment in sight, provided he/she has the required flight visibility. Obviously, this leaves a certain amount of room for interpretation. If you find yourself in such a situation, and there’s any doubt about whether to proceed (particularly if you’re not familiar with the local terrain and landmarks), it’s best to opt for the missed approach.

It’s also worth thinking about why the “fly visual” segment exists in the first place. Why did the designers of the approach essentially choose to “slide” the entire approach away from the airport by the distance of the visual segment? In many cases, the underlying reason is that terrain in the missed approach area would necessitate unreasonably high minimums if the MAP were in its normal position. By displacing the MAP a few miles, the designers can build a missed approach segment that doesn’t have terrain problems (a situation well illustrated by the NDB/DME or GPS-A approach at Hailey, Idaho).

Of course, the terrain is still out there, and the danger for pilots flying such procedures is that the unanticipated need to initiate a missed approach beyond the MAP can lead to obstruction conflicts (or, to put it more bluntly: a collision with a mountain).

The bottom line? For procedures like the one at Hailey, never continue the approach past the MAP unless there’s absolutely no doubt about the outcome.

Sounds like fun. Not! Imagine having 1/2 mile visibility and coming to the end of your RNAV highway in the sky, yet being permitted to continue flying visually without the having the airport in sight. TLAR (”that looks about right”) navigation at its best.

The scary thing about these approaches is that they occur in mountainous areas. By definition, these areas having high density altitudes in the summer and are prone to icing in the winter. A mountainous approach is one time I would want to start my missed approach segment earlier rather than later in order to assure adequate terrain clearance during the climb.

The RNAV Approach Quiz is free, and it was far more informative than I had anticipated. Normally I breeze through these things with nary a thought, but I really had to stop and think about some of the questions. And I must admit there were some things in there I didn’t know.

A while back, I made a casual suggestion John at Aviation Mentor.  He often writes about instrument flying in “glass panel” aircraft, something that is near and dear to my heart since this is one of my specialties at work.

I’d been noticing that more and more instrument approach procedures where being developed with weird minima.   There were columns for LNAV, LNAV/VNAV, RNP, LPV, and more.  Back in the late 90’s when I got my instrument rating, these acronyms weren’t even a gleam in the eye of their creator.  Now they’re all over the place, and CFIIs have to ensure their students know what these things mean.

I’ll let John take it from there.  Read his article and tell me it doesn’t sound confusing.  LNAV/+V?  C’mon people.  The FAA and equipment manufacturers can’t even agree on whether or not an LPV approach is “precision” or “non-precision”.

I’m glad I suggested this as a topic. One observation I have on the whole LNAV/VNAV thing is that in the past, when new approach capabilities were introduced to the IFR world, the equipment was usually in place at or before the time when the approaches starting appearing.  For some reason, it’s backwards this time.  There are a ton of RNAV approaches with VNAV glideslopes depicted on the plate, yet as far as I know, very few — if any — aircraft are yet certified to fly them.

Since the approaches have to be tested before they’re approved for the general public, I wonder if the FAA is the only one with the capability to fly these things. John indicates that he hasn’t flown any VNAV capable equipment yet.  I haven’t either, nor do I know anyone who has done so in the soup.  Between the two of us, we’re operating in the largest metropolitan areas in the state of California.

I completely agree with his concerns about the way this capability is being integrated into our cockpits.  The terminology is confusing, and it’s a terrible idea to have a pilot approaching a final approach fix without an idea of whether he’ll be shooting a precision or non-precision approach.

If the GPS receiver decides it doesn’t have the required geometry for a glideslope approach, the downgrade is annunicated at the worst possible moment.  There is no more likely time for a pilot to miss a flashing message light than when he’s about to pass the final approach fix.  ATC is providing final vectors, issuing an approach clearance, approach mode should be armed/arming, the pilot is running the “T”s and the Before Landing checklist.

I’ve always had a suspicion that these things were developed and tested in a perfect-world environment, something that those of us in busy airspace never see.  People who can afford a $65,000 glass panel are not aviating in the middle of nowhere, they’re flying in busy metropolitan areas and mixing it up with large jets and controllers who vector them as close as possible to the final approach fix.

The lack of a glideslope is not enough of an indicator; glideslopes fail for more than one reason.  Is it a software bug?  Did we load the wrong approach?  Or fail to activate it? Is there a hardware problem?  A RAIM alert?  This is not a good place for head-down time and button pushing.  These things should be designed to minimize that, not maximize it.

It seems to me it might be better to make critical annunciations more obvious to the pilot.  A tiny flashing “message” in the lower corner of nearly four square feet of computer screens is not sufficient.  My students miss these annunications all the time.  In fact, they actually learn to ignore them because most of the annunciations are nuisance alerts.  Airspace, schedulers, etc.

Pilots need to preconfigure the avionics suite so messages are minimized.  That means understanding the auxillary and setup pages.  We also need better education on GPS approaches.  If you fly a TSO-129 GPS equipped aircraft, you own it to yourself to read AIM 1-1-19, 1-2, 5-4-5(d), and other related sections of the Aeronautical Information Manual

A logical system for integrating new approach technologies without just throwing new acronyms and minima onto hundreds of approach plates would go a long way toward preparing pilots before the approaches were out there.  From my experience, it’s easy enough for a pilot to inadvertently select the wrong minimums without adding all these new ones to the mix.

One look at an RNP approach (like the one above, from Palm Springs) should be enough to convince anyone of the capability GPS can provide.  But those who don’t have an airline training department and budget behind them must proceed with caution, lest the road to GPS nirvana turn into GPS hell.