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Do you see that frustrated look on our faces? That's us trying to figure out what our plane is doing. Or more specifically, what the G1000 flight deck is doing.
Technically Advanced Aircraft give you an incredible amount of information in the air. That makes flying, and especially IFR flying, safer than ever before.
But at the same time, you need to know how to use the technology. If you don't, it can bite you in the butt, and get you into a situation where you're saying "what's it doing now?!".
Here are three common scenarios that can leave any pilot flying a technically advanced aircraft wondering what's going on. Our examples are specific to the G1000 - but many TAA GPS and navigation systems are similar.
Most of the waypoints on a GPS approach are "fly-by" waypoints, which means you might not fly over them. Or get even close to them, for that matter. Your GPS calculates the most efficient turn on to your next course, and then 'cuts the corner' to make a smooth turn between course segments.
While it makes for smoother route segments, it can also leave you scratching your head. You'll experience this on both GPS approaches, and ground-based NAVAID approaches when you use GPS for guidance on the initial and intermediate segments.
Look at this example of an approach we were flying into Telluride:
On the LOC 09 approach at KTEX, ETL is the initial approach fix. But because of the angle we were flying toward ETL, GPS turn anticipation kept us from getting close. In fact, we were more than a mile from ETL as we flew the approach. Which is perfectly fine, it's just turn anticipation doing its job.
The only place this won't happen is with fly-over waypoints. On approach charts, they appear as a star with a circle around them. And if you have a fly-over waypoint on your chart (most missed-approach points are) your plane will fly directly over the point before making the next turn, no matter what angle you approach it from.
When you're flying a VOR approach, you can load the approach through your database and get advisory navigation from your GPS.
And that's really nice to have, because it can make navigating a VOR approach much, much easier. Especially when it comes to arcs and procedure turns.
But there's a catch. Since most VOR approaches are no longer "VOR or GPS RWY XX", it means you can't use GPS as your sole means of navigation from the final approach fix inbound.
And unlike localizer or ILS approaches, when you load a VOR approach into the G1000, it won't automatically switch your CDI from the magenta GPS course to the green VOR course as you approach the Final Approach Fix (FAF). You have to manually set up the CDI as you approach the Final Approach Fix.
So what are you supposed to do? There are two ways to handle it.
The AIM prohibits you from using GPS (even if it's IFR approach approved) as the sole source of navigation on a VOR approach - one that doesn't say "or GPS" in the title. But, it does allow you to use GPS for navigation, as long as you tune and monitor your position for final course alignment using VOR indications. So - the VOR must be operational, and you must have it tuned and displayed, and it must show that you are on course. But, as long as you do that, you can continue to use GPS course guidance. For the technical details, see AIM Chapter 1-2-3 "Use of Suitable Area Navigation (RNAV) Systems on Conventional Procedures and Routes" - paragraph "c." Make sure to read the "Notes" section.
First, you can manually switch your CDI from GPS to VOR course guidance prior to the FAF. It's not the worst thing in the world, but it does require you to remember to switch before you cross the final approach fix. And it also means you may need to make a course adjustment when you switch from GPS to VOR, because the VOR course may not be pre-selected. And, if you have your autopilot connected, you'll need to re-set your lateral nav by pressing "APR" once you change the CDI source.
The second way you can handle it is by monitoring the VOR using bearing pointers - like a RMI. Check out this this example of one we flew in Cortez, CO:
As long as your VOR based bearing pointers show that you are on course, you can stay in GPS mode. In our example above, we did it by using the bearing pointers to monitor VHF Nav 1 and 2, all the way to the runway. In this case, we don't need to cycle the CDI from GPS to VOR. And, if we're using an autopilot or flight director, the lateral mode doesn't need to be reset. It's a much simpler solution.
Flying a stable, constant glideslope is much easier than resetting your power and pitch as you make multiple stepdown altitude changes.
That's why vertical path navigation is such an amazing tool. By arming VPATH, your GPS can fly a constant vertical path from fix-to-fix. You don't need to remember to level off, increase power, and then start descending again.
But if you're using an autopilot or flight director, and you don't bug a lower altitude before VPATH reaches your currently selected altitude, you'll find yourself leveling off in the middle of your VPATH profile:
This makes sense, but in practice, it can be easy to get behind. As you approach a fix, you'll need to set your altitude bug to the next lower altitude before you cross - essentially bugging the altitude early. Which also means that you have to make a mental note not to descend below your current segment's minimum altitude until you cross the fix. And - if you get distracted by a radio call or checklist before you set the bug - you're leveling off.
Keep in mind, however, that glideslope mode (GS) or glidepath mode (GP) is different. It doesn't matter what altitude you've bugged when you intercept a glideslope or path. In GS or GP mode, your plane will descend along the glideslope or path all the way to the ground, no matter what altitude is set.
TAA aircraft give you the ability to do more than ever before. But if you don't understand what's going on, you can get yourself in trouble in a hurry.
Like most things, the best way to stay on top of it is practice. So the next time you're up, load an approach you've never flown before. Try using vertical path navigation for your next descent into an airport. You never know when you might really need to use them.
Colin is a Boldmethod co-founder, pilot and graphic artist. He's been a flight instructor at the University of North Dakota, an airline pilot on the CRJ-200, and has directed development of numerous commercial and military training systems. You can reach him at firstname.lastname@example.org.