Navigation Database Currency (Part Two)

The Flight Planning Page

Every FMS unit includes a page dedicated to entering a flight plan. Typically, entering a flight plan is a simple matter of “filling in the blanks”—entering the en route waypoints and instrument procedures that make up the planned route.


En Route Waypoints and Procedural Waypoints

Entering a flight route into the FMS unit requires you to enter the waypoints that define your route. FMS distinguish between two kinds of waypoints: (1) waypoints that are published, such as departure, arrival, or approach procedure points; and (2) user defined waypoints. The approved system software (the internal programming) allows the pilot to manually enter airport and en route waypoints. However, you are prohibited by the software from entering (or deleting) individual waypoints that define a published instrument procedure, since misspelling a procedural waypoint name or deleting a procedural waypoint (e.g., final approach fix) could have disastrous consequences. Any changes to the selected database approach procedure will cancel the approach mode. Changing to go direct to a waypoint will not, in most units, cancel the approach mode (such as receiving radar vectors to final and bypassing an intermediate fix).

Entering En Route Waypoints

Looking at the planned route in Figure 3-8, it is apparent that San Carlos airport (KSQL), and SUNOL and TRACY intersections are not part of any instrument procedure that pertains to the planned flight. These waypoints can be entered into the unit, as shown in Figure 3-9.

Figure 3-9. Entering en route waypoints in the flight plan.

Figure 3-9. Entering en route waypoints in the flight plan.

The remaining waypoints in Figure 3-8, starting with the initial approach fix at ECA, are part of the Oakdale GPS approach procedure. Waypoints that are part of a published instrument procedure are entered by a different technique that will be introduced later. In some cases, you navigate along an airway that contains a string of waypoints, such as the one shown in Figure 3-10.

Figure 3-10. Entering waypoints along an airway.

Figure 3-10. Entering waypoints along an airway.

In this case, it is only necessary to enter waypoints along the airway that represent course changes. In Figure 3-10, REANS intersection is a changeover point that joins the Pomona 073-degree radial and the Twentynine Palms 254-degree radial. For this airway segment, you could enter POM, REANS, and TNP, keeping in mind that the remaining waypoints do not appear in the programmed route.


Entering Airways

More sophisticated FMSs allow you to enter entire airways with a single action into the unit. When an airway and endpoint for that airway are selected, all waypoints that occur along the airway are automatically inserted into the flight plan. Figure 3-11 shows a navigation unit that allows airways to be selected.

Figure 3-11. Inserting an airway into a flight route.

Figure 3-11. Inserting an airway into a flight route.

Entering Procedures

Every IFR-capable FMS offers a menu of published instrument procedures, such as departures, arrivals, and approaches. When you choose one of these procedures, the FMS automatically inserts all waypoints included in that procedure into the flight plan. Figure 3-12 illustrates how you might choose an approach procedure using one popular FMS.

Figure 3-12. Inserting published instrument procedures into a flight route.

Figure 3-12. Inserting published instrument procedures into a flight route. [click image to enlarge]

Risk: Taking Off Without Entering a Flight Plan

The convenience of the FMS, especially the “direct to” feature common to all units, creates the temptation to program only the first en route waypoint prior to takeoff and then enter additional waypoints once airborne. Keep in mind, however, that no matter how skilled you become with the avionics, programming requires “heads down” time, which reduces your ability to scan for traffic, monitor engine instruments, etc. A better strategy is to enter all of the flight data before you take off.

Reviewing the Flight Route

Once a route has been entered into the FMS, the next step is to review the route to ensure it is the desired route. It is particularly important to ensure that the programmed route agrees with the pilot’s clearance, the en route and terminal area charts, and any bearing, distance, time, and fuel calculations that have been performed on paper.


Catching Errors: Using the FMS Flight Planning Function To Cross-Check Calculations

Using the FMS’s flight planning function to check your own flight planning calculations is one example of how advanced cockpit systems can decrease the likelihood of an error. Alternatively, cross-check the computer’s calculations against your own. (Remember the old computer programmer’s adage, “Garbage in, garbage out (GIGO).”)

The flight planning page can also be used to review the route that you entered into the FMS, as illustrated in Figure 3-13. Be sure to check at least four things when reviewing your route.

Figure 3-13. Reviewing the flight route.

Figure 3-13. Reviewing the flight route.

Check the Waypoints

On the flight planning page, compare the sequence of waypoints with that prescribed by his or her clearance. Are any waypoints missing? Did you mistakenly include any extra waypoints in the route? Did you misspell any waypoints? Did the computer mistakenly include any extra waypoints in the route?

Check the Distances

On the flight planning page, you can see that the computer has calculated the distances between the waypoints in the route. These distances can be checked against the en route charts. A common error is to misspell the name of a waypoint and, thus, mistakenly enter a waypoint not appropriate to the planned route (e.g., KHEE versus KHEF). Checking the waypoint distances for unusual numbers is a good way to spot these errors.

Check the Desired Tracks

On the flight planning page, you can also see the course that the computer has calculated between waypoints along the route. A desired track between two waypoints represents the shortest path between them. The desired track between two waypoints may differ from the course seen on the aeronautical charts. In fact, there may be a difference of several degrees between the desired track and the airway course. Some of this difference may be due to the method in which the FMS accounts for magnetic variation. Some units use an internal database and interpolate, while others compute all values from tables.

Unlike the world as printed on paper charts, the earth is round, not flat. The shortest distance between two points on the earth is not a straight line; it is an arc, as shown in Figure 3-14.

Figure 3-14. A great circle route.

Figure 3-14. A great circle route.

The shortest route between two points on the surface of the earth is called a great circle route. To find the great circle route that connects two points, imagine a geometric plane cutting through the earth that passes through the two points and the center of the earth.

On the great circle route from SFO to LGA in Figure 3-14, departing SFO, the desired track is a little less than 90 degrees. Upon arrival at LGA, it appears to be greater than 90 degrees. The desired track heading is constantly changing since it is a circle, not a line. If, however, the difference exceeds several degrees, you need to investigate further to determine the cause.


Check for Route Discontinuities

Some FMS units do not automatically assume that you wish to fly between each of the waypoints that have been entered into the flight plan. When there is a question about how to proceed from one waypoint or instrument procedure to the next, some units insert a “discontinuity” in the programmed route. A route discontinuity indicates that the FMS needs further input from you about how two route segments should be connected. A route discontinuity is shown in Figure 3-15. If you wish to proceed directly from the waypoint that appears before the route discontinuity to the waypoint that appears after, you can simply delete the discontinuity, as shown in Figure 3-15.

Figure 3-15. A route discontinuity and deletion.

Figure 3-15. A route discontinuity and deletion.

If the route discontinuity is left in the flight plan, the unit computer will not provide guidance beyond the waypoint that occurs before the discontinuity.

Maintaining Proficiency: Aeronautical Knowledge

It is easy to use an FMS without performing your own calculations for courses, headings, times, distances, and fuel used, but studies have demonstrated that aeronautical skills that are not practiced regularly quickly fade, regardless of experience level or certificates and ratings held. Abnormal and emergency situations (e.g., electrical failure) do occur, so it is important to maintain proficiency in at least making “rule of thumb” calculations on your own.