Setting the CDI on a Conventional Approach (The “Kill Switch”)

If you fly an aircraft with an IFR-approved GNSS, you probably use that “suitable RNAV system” to help you fly all types of approaches, including ILS, LOC, and VOR procedures. In fact, if your aircraft isn’t equipped with DME or ADF, using an IFR-approved GNSS system may be the only way for you to fly many conventional procedures.

“Suitable RNAV systems” based on GNSS are described in AIM 1−2−3. Use of Suitable Area Navigation (RNAV) Systems on Conventional Procedures and Routes, AC 90−100, AC 90-108, and other FAA references.

For more information about the use of GPS along the final approach course of a VOR or NDB approach, see Use of GPS on Conventional Approaches (Update)

A critical step in flying conventional approaches while using GNSS to fly transitions/feeder routes is ensuring that the proper guidance is shown on the PFD/HSI as you intercept and then fly the final approach course.

For example, as shown below, when flying the LOC RWY 17 approach at Aurora, OR (KUAO), you could use the GNSS for course guidance as you fly the charted transition from the Battleground (BTG) VOR.

Some systems can automatically switch the CDI from the “magenta line” shown when using GNSS signals to “green needles,” usually labeled VOR/LOC, as you intercept final. But you must always monitor the avionics and, if necessary, use the CDI button (or other switch for your system) to change to VOR/LOC “green needles” before you join the final approach course.

For more information about guidance along the final approach course, see Use of IFR GPS on Conventional Approaches here at BruceAir.

Unfortunately, many pilots fail to confirm this critical step, which often occurs during a high-workload phase of an approach. For example, just as you are about to intercept the final approach course, ATC may issue a rapid-fire vector and approach clearance (“Fly heading 130, maintain 2,000 until established…”), you can be distracted while making a late configuration change, or while switching frequencies to the tower or CTAF.

In fact, this error is so common that many pilots and instructors call the CDI switch the “kill button” (or a similarly ominious name) to emphasize its importance.

I use a graphical reminder to help me ensure that I switch course guidance in plenty of time for a smooth intercept.

Like many pilots, I use a tablet and an aviation app (in my case, primarily ForeFlight) to display charts. Those apps typically have an annotation feature that lets you mark up charts to emphasize important information.

For example, on this chart for another approach at KUAO, I’ve noted a temporary change in minimums.

To remind myself to switch the CDI to “green needles” on conventional approaches, I use the annotation feature to draw a transparent green line along the final approach course.

I mark up the charts for conventional approaches during my preflight planning as I review weather, NOTAMs, procedures that I might fly, and other details.

I organize approaches that I fly often into binders in ForeFlight (other apps have a similar feature), and the markups are preserved between flights, so I don’t have to repeat this process for most of the procedures that I fly.

Because RNAV (GPS) approaches don’t require changing from GNSS guidance, I don’t highlight the final approach segment on those procedures.

To avoid cluttering charts, I also don’t mark the intial steps of a missed approach in magenta to signify that I can return to GNSS guidance to fly the miss, regardless of the type of approach. But if you’re in IFR training or new to using GNSS under IFR, highlighting the miss in magenta might be a useful reminder.

Changes to Flight Plans with Procedures in GTN System Software 6.x

Garmin has released updated system software (version 6.11) for the GTN series of navigators. The software includes several new features. One of the most important changes, at least for day-to-day operations for typical general aviation pilots, is how loading (or activating procedures) affects departure and destination airports in flight plans (routes).

To learn about and practice using the new features, download the latest version of the free GTN 750 PC Trainer Lite from Garmin. The download includes updated manuals (PDFs) for the GTN series avionics that describe the new features in version 6.x.

I have experimented with how the new system software in the free GTN 750 PC Trainer Lite available from Garmin, and the following examples illustrate the changes and offer suggestions to help you adapt your personal techniques for using a GTN-series navigator in the cockpit. In particular, I offer suggestions for displaying information about your destination airport (frequencies, current weather, and so forth).

To learn about the new ad-hoc hold feature in the updated software, see Flying Ad-Hoc Holds with a GTN 750 here at my blog.

Basics of the Change

First, here’s a note in the updated Pilot’s Guide for the GTN 750 that describes how software version 6.x changes flight plans (routes) when you load an approach (or, it turns out, a departure procedure).

Now let’s look at how this change affects when and how you load and fly a typical instrument approach.

A Typical IFR Flight Plan

Suppose you plan to fly from Boeing Field (KBFI) in Seattle, WA to Spokane International Airport (KGEG) in eastern Washington. Here’s a route across the Cascades that I often fly in my normally aspirated Beechcraft A36.

Note that the first and last waypoints in the flight plan are the departure airport (KBFI) and destination (KGEG). ATC typically assigns a SID when departing Boeing Field. When runway 13R is in use for IFR departures, your clearance includes the KENT7 (or the current version) SID, which you load as follows.

Note that after you load the departure, KBFI no longer appears as a waypoint in your current flight plan. The first waypoint in the flight plan is now the runway ((RW13R), which is the first fix in the KENT7 SID. The IDs of the departure and destination airports, however, remain in the title of the Active Flight Plan.

Here’s the first tip. If you use your GTN navigator to retrieve frequencies and other information about your departure airport, collect that data before you load a departure procedure.

Now assume that you have departed KBFI, followed the SID and ATC vectors to join V2, and proceeded to a point west of Spokane where you are preparing for the arrival and approach at KGEG, say the RNAV (GPS) RWY 21 Y approach.

Given that you’re approaching KGEG from the west, ZOOMR is good fix to choose, at least initially, as the transition for the approach. ATC will probably provide vectors, but with all the fixes from the west now in the flight plan, it’s easy to accept a clearance direct to any of the fixes or legs along the path to the final approach segment.

Notice that after you load the approach, the GTN removes KGEG from your active flight plan—unless the active leg of your flight plan includes the airport. Versions of the system software prior to 6.x always added the approach name and fixes for an approach below the destination airport.

A Logical Change?

The change in behavior in version 6.x may disrupt your habits at first. But it also may reduce the potential for errors when you load and fly an approach (or DP) under typical circumstances.

The new behavior provides a seamless transition from waypoints in en route section of your flight plan to fixes in an approach. You no longer have to scroll below the destination airport in the active flight plan list to select an initial fix or to activate a leg of the approach you’ve loaded into the GTN.

A Change in Tactics?

The new behavior described above may lead you to change your basic technique for loading an approach.

I have long advocated loading procedures as early as possible—even before taking off if the destination is nearby—to reduce your workload during busy phases of flight. The new behavior in GTN software version 6.x, however, suggests a change in tactics, at least under some circumstances.

If you can determine well in advance which approach you prefer to fly—in-cockpit weather can give you an early alert about which runway is likely to be in use long before you can receive the ATIS or AWOS (that is, the one-minute weather at a non-towered airport)—then loading the approach you prefer or reasonably expect to fly is still a good idea. Just take a moment before you load the procedure to retrieve and note frequencies and other details about your destination airport from the GTN.

Pilots arriving or departing an uncontrolled airport that has automated weather broadcast capability (ASOS/AWSS/AWOS) should monitor the broadcast frequency, advise the controller that they have the “one−minute weather” and state intentions prior to operating within the Class B, Class C, Class D, or Class E surface areas. (AIM 4-4-6)

ONE-MINUTE WEATHER− The most recent one minute updated weather broadcast received by a pilot from an uncontrolled airport ASOS/AWSS/AWOS. (P/C Glossary)

If you prefer to wait until you are closer to the airport, or if ATC clears you direct to the airport or issues vectors before initiating an approach clearance, you can delay loading the approach.

If you wait until the active leg of your flight plan includes the destination airport, the GTN adds the approach below the destination airport, just as it did prior to version 6.x.

Or, as shown below, you can load a procedure early and then add the destination airport to the bottom of your current flight plan, so that the airport is still available as a reference and to provide easy access to the information about the airport in the GTN’s database. Here I’ve added KGEG below GANGS, the MAHP for the RNAV (GPS) RWY 21 Y approach. It’s easy, as before version 6.x, to touch the airport ID and then select Waypoint Info.

Add an Alternate?

The change in version 6.x also simplifies adding an alternate to your flight plan.

Suppose the weather at KGEG is close to minimums as you begin your arrival. Adding an alternate airport to your flight plan before you miss the approach could reduce your workload during a critical phase of flight.

Here I’ve added Walla Walla, (KALW) as my alternate after the MAHP at GANGS.

Now I can quickly retrieve information about KALW and even load an approach as soon as I get a new clearance from ATC.

This technique would also be handy during training flights, when you fly several approaches, either to the same airport or close-by fields.

Other Methods for Retrieving Airport Information

If you prefer not to fuss with the way version 6.x handles airports in flight plans that include procedures, you can still retrieve information about airports from the GTN’s database, even if your departure and destination airports are no longer in your active flight plan.

For example, touch the map, scroll to display an airport, and touch an airport symbol. Touch Waypoint Info to display details (frequencies, current weather, runways, NOTAMs, and so forth) about the airport.

You can also use the Nearest Airport feature (available from the Home screen) to gain quick access to details about your destination—provided you’re not too far away.

Or you can use the various search option in the GTN to find an airport and retrieve information about it.

More to Come

I’ll have more to say about the updated system software after I’ve had it installed in my airplane and explored the new features on test flights. Stay tuned.