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Why you need to fly TKE: if you have a Garmin GPS and find that tracking courses perfectly takes more than a passing thought, then you're working too hard.

In the realm of flying lore, there are few secrets. Useful techniques tend to spread quickly. This makes it all the more satisfying to discover a secret buried in our avionics that dramatically eases flight under certain circumstances.

The track angle error (TKE) field of Garmin 400/500 navigators is just such a diamond in the rough. While this technique is most valuable in the context of flying a partial-panel approach, it can be tremendously useful even when all systems are go. For example, flying an approach in an airplane without an electronic HSI that overlays track is a piece of cake if TKE use is mastered.

A Few Definitions

Track (TRK), bearing (BRG), and desired track (DTK) are often confused by pilots. Yet each is unique and specific, and understanding exactly what they mean is essential to mastering TKE. TRK is the path across the ground our aircraft is taking at this moment. If winds are completely calm, TRK will equal heading, since where we point is where we go. In the real world, TRK will typically be anywhere from two to 20 degrees different from heading, depending on the crosswind component.

BRG is infrequently used in modern IFR navigation, but understanding the concept is necessary to move on. BRG is simply the magnetic measurement between the aircraft's current position and the waypoint in question. Draw a line from the air plane, right now, to the active waypoint and measure it against magnetic north. That's BRG. On downwind to Runway 18 you might be flying 360, but when you were abeam the touchdown zone, your bearing to that spot would be 090.


DTK is the GPS equivalent of course (CRS) when flying by VOR. Unlike BRG, it has nothing to do with where the aircraft is right now. If an approach has a segment with a DTK/CRS of 090, it will be 090 whether we're smack in the center of the approach or way off to the side. We need to look at the CDI to tell us where we are with respect to DTK.

All of this leads up to TKE. TKE is simply the numerical difference between DTK and TRK, with a left or right indication of which way TRK needs to change to equal DTK. On that approach with a DTK of 090, if we're tracking 097, then TKE is "[left arrow] 007." This means: Turn left seven degrees and TRK and DTK will be equal. If your TKE already matches your DTK, TKE will display 000. If the CDI is centered at the same time, you're on course and you're going to stay on course. If the CDI is not centered, a TKE of 000 will result in paralleling the course. When we're off course, we need to have some intercept angle, so in this case 000 is an undesirable TKE.


TKE Fixes

What about when the CDI is centered but TKE is not zero? That means you may be on course right now, but that won't be true for long. Turn in the direction the TKE field tells you, however many degrees it tells you.

Remembering that everything in GPS world lags a second or so, don't wait until you see 000 to roll level or you'll overshoot. A useful trick is that at five degrees of bank and 100 knots, turn rate will be one degree per second. So if you see a TKE of 004 [right arrow], roll into a five-degree bank to the right, count four seconds out loud, and roll level. Then check the TKE, and if necessary, make further corrections. Repeat ad nauseam.

Obviously, the CDI is not going to always be centered, and some course correction may occasionally be needed. Here's another area where TKE shines. Read the following carefully: Whichever way TKE is telling you to turn, that's the way your CDI will move over time if you don't turn. With a TKE of [left arrow] 001, the CDI will move slowly left. A TKE of 050 [right arrow] will result in rapid needle movement to the right. This is true whether you are left of course, right of course, or dead centered on course.

This fact makes course corrections simple. As long as you're still within approach tolerances, and only need to make small corrections, make the TKE display about 005, with a [left arrow] or [right arrow] indication, as you need, to make the CDI come back to center. Just before the CDI centers, roll out the TKE to 000 and, presto, you're on course with any wind correction automatically entered.

Simple Partial Panel

TKE makes tracking a course partial panel a piece of cake. No more watching needle movement and trying to guess a heading change.

A PFD failure in a glass cockpit aircraft or a failure of only the HSI in a six-pack aircraft means you still have an attitude indicator, so flying by TKE is no harder than using the HSI. It may even be simpler once you get used to it.

If you're down to the turn coordinator for roll control, it's not much harder. Focus on maintaining the symbolic wings perfectly level when TKE is where you want it to be, and don't let them show more than a half-standard-rate turn if you need to change the TKE value.

TKE technique is just obtuse enough to require thought and practice. Yet its complexity makes you feel even more like a Kung Fu Master realizing some ancient secret when it clicks. It actually can be a bit boring when you realize how easy it is to keep course nailed without even a glance at the HSI.


We should be able to scan the TKE field and the CDI displayed on the NAV 1 page of the Garmin and derive: a) if things are good; and b) if not, what to do.

This situation below is desirable. The CDI is centered and TKE is zero. We're on course and not going anywhere. Wind correction is taken care of automatically.


This next situation is not so good. The needle will start moving from its essentially centered position if we don't turn about 20 degrees left, and soon.


Here we have a good intercept. The needle is less than half-scale deflection, so a five-degree intercept is perfect. The TKE arrow is pointing left, which is the way we'd like the CDI to move.


This one is a bad situation getting worse. We're at nearly half-scale deflection and moving away from the course at a good clip. We need to turn at least 1.5 degrees right: 10 to parallel the track plus five to establish an intercept angle.


If your NAV 1 page doesn't have the TKE field displayed, hit the MENU button, then select "Change Fields?" The cursor will flash over the first field. Moving the large knob will change which field you want to alter, while turning the narrow knob will pull up a menu of options.

If you're hungry for some more practice, you can find three pages of examples on my website, at

Neil Singer is a mentor pilot in the Northeast (
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Title Annotation:TRICKS O' THE TRADE; track angle error
Author:Singer, Neil
Geographic Code:1USA
Date:Sep 1, 2009
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