Last month I discussed the use of IFR GPS in OBS mode, a logical place to start transition from conventional VOR/Localizer (VLOC) navigation to IFR GPS. Once full GPS use has been embraced, however, OBS mode has limited application: missed approaches, procedure turns and holding patterns; it is not how one actually proceeds IFR enroute or makes approaches. This month, it's time to look at Leg mode, the software designed for those more primary functions.
To start with, it's important to note that IFR GPS units start up by default in Leg mode; generally speaking, it's the standard way to get from here to there.
A second basic observation: users with VFR GPS experience start with a good understanding of Leg mode. Whenever you press the "direct to" (D) button, that's the software system you are starting up.
There are two ways to start the leg process. The first and simplest: press D and enter a destination waypoint. This generally works well for VFR, where straight line flight from start to finish is the norm. The procedure is less likely to suit the needs of an IFR clearance, however, where interim waypoints, like VORs and intersections typically define more precise routes of flight.
FLIGHT PLANS
To accommodate more sophisticated route structures, IFR GPS units are designed to accept the creation and subsequent activation of flight plans with multiple waypoints. Each waypoint pair is interconnected by a leg. Flight plans can be programmed well in advance of need, saved and then retrieved for use at the start of the flight. The specifics for creation and activation differ markedly with each manufacturer, so practice with individual units is essential.
The flight plan feature shows off the great advantage offered by GPS: the ability to identify and plot to virtually any destination or interim checkpoint anywhere on the planet.
The first task in flight plan creation is to become familiar with the knobs and dials that permit alphabet and symbol selection as a you spell out the unique identifier of each waypoint (WP). IFR WPs (airports, navaids and reporting points) are stored in the GPS database, so you can expect some helpful prompting as you get close to completing the spelling of each one.
Next comes saving and storage of the flight plan. Without this step, all your labors are lost when the avionics master is turned off.
Finally, we come to waypoint deletion and insertion. Mastery of these skills is essential: as often as not, you will be asked to change flight plans before IFR use, depending on the whims of ATC and the actual clearances they decide to deliver.
The delete/insert process will serve as a good introduction to the "cursor" concept, a key feature included in every IFR GPS unit. Upon entering cursor mode, at least one knob function changes to permit scrolling up and down flight plans and other lists in order to select points to delete, insert or examine.
Deletion and insertion are functions with which you should become very familiar to ensure you are able to deal comfortably and quickly with enroute changes to IFR clearances. Failure to invest adequate classroom and simulator time in these steps can convert IFR GPS from a helpful tool to a downright liability.
MAPS
More than any other feature of GPS, moving maps are singled out by general aviation users for the most praise; there is a near-universal phrase used to describe the benefit: "situational awareness." In English, this translates to, "I don't get lost as much." After all, every nav aid, from the aural range of the 1930s through inertial navigation, is used to provide situational awareness. GPS maps are just easier to use and more idiot proof.
Once a flight plan is activated, the first and all subsequent legs show up on the map as straight lines connecting the waypoints. You can elect to view the result two ways: north at the top of the screen ("north up"), or next waypoint at the top ("track up"). I firmly believe that north up is the right choice, but sense I am in the minority.
The difference has more than just aesthetic overtones. The moving maps are not intended or authorized for use as primary nav sources: they are "informational" only. You do not track airways, skim the edges of restricted areas or skirt regulated airspace with them as your ultimate source of position data.
By contrast, you do all those things with navaids and aviation charts, all of which are drawn north up. It is a standard navigation skill to learn to use a north up map even when flying south--it doesn't take long to learn, and is a heck of a lot easier than twisting paper charts around inside the cockpit to get track up (it also keeps the charts easier to read). Holding a paper chart that is aligned north up and comparing its data with an electronic map aligned with track up is awkward, and I suspect everybody would be better off keeping their electronic maps in agreement with the real authority--the paper ones.
CONCERNS ABOUT MAPS
Electronic maps lack the clarity and detail available on paper charts.
An electronic map is a supplemental aid--it would be foolish to depend on one exclusively and launch VFR without corresponding paper charts. A similar choice made for IFR flight goes well beyond foolishness, somewhere into the realm of brain dead. Paper charts don't go blank during electrical failures.
A final concern with electronic maps is the risk that some pilots may come to depend on map displays exclusive of CDI or other course information. These individuals may prove incapable of using standard nav indications in the event of map failure, a risk that flight instructors will increasingly need to learn to anticipate.
GPS DIRECT
As I have described them to this point, GPS flight plans mimic the paper "flight logs" you are accustomed to creating for IFR flight. Used this way, GPS is just substituting for the VOR system, with only its electronic map and accurate enroute performance data to distinguish it from earlier systems. Fortunately, there is more: the "from anywhere to anywhere" capability of GPS permits remarkable freedom when compared to standard VOR airway use.
The first time I used IFR GPS to really good effect I was in an unfamiliar part of the country, struggling to consult airways, enroute fixes and routes I had never before used. Weather was moving in, so there was pressure to get going.
"Why not just file GPS direct Sioux City?" suggested a hovering CFI. "They'll give it to you at 6000 feet." Great simplicity followed, like sunlight breaking through the fog; this was leg navigation at its best.
When the clearance arrived, it was exactly as ordered: a departure procedure, then direct to the destination, with no charted courses to intercept and no nav aids to locate. The procedure was made possible by two technical advances: radar and GPS.
Without radar, direct IFR flight is not permitted--nor would it be safe. The airways and other charted courses have the advantage of offering proven routes with guaranteed terrain separation and navigation reception. Without radar to monitor progress, the FAA quite sensibly limits IFR flight to those routes. With radar monitoring, sufficient altitude, and a nav system capable of bridging the distance, however, the IFR rules permit pilots to stray off charted routes, making extended direct flight a reality.
When enroute weather rears its head, GPS direct really comes into its own, permitting wide excursions without loss of signal or "situational awareness." NOTE: it is essential to learn how to restore the original flight plan after such an excursion.
PLANNING
The freedom of GPS direct carries hidden risks. Because the need to locate VORs, airways and other charted features is eliminated during the planning phase, it is tempting to launch without completing other essential activities standardly involved in pre-flight planning--like estimates of ground speed, times enroute, and fuel needs. Although the GPS unit will provide some of that information, like ground speed and ETE, once you are up and running, it won't do the job on the ground, and that's the only place you can buy and add fuel to the tanks.
There is another standard feature of conventional airway use that can be lost with GPS direct: the ability to orient to the interim reporting points that crop up on most airways. Without those pre-charted checkpoints, GPS users need to develop alternate means of remaining oriented to their progress during the flight.
Simple: the moving map, you say. That's an inevitable response, but I again caution you against relying wholly on an electronic screen. You need to retain orientation to paper charts as well.
GPS direct is a shortcut, not a revolution.
SAFETY CONCERNS
By now, you may be able to sense an underlying theme in these GPS articles: my concern that increased automation and improved navigation displays may confuse thoughtless pilots into the false belief that major threats to aviation safety have been diminished, or perhaps even eliminated. I can't think of one. Pilot error is the #1 cause of tragedy; it is controlled by thoughtful planning and consideration of consequences, and there aren't any machines yet built that will do any of that.
Next up: GPS approaches.
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