Later, when VOR navigation was introduced, radar coverage was limited, and pilots could still intercept most courses any way they chose. So, they continued to use double-the-angle-off-the-bow navigation.
Today, with expansive radar coverage and high-density traffic, controllers often assign specific headings for course intercepts. If you are not flying an assigned heading, you are probably flying on a specific VOR or GPS course, hopefully with a centered course deviation indicator.
Unfortunately, some pilots fail to stay on course because they don't fly a constant heading or compensate for winds aloft. When I see that a pilot has a full-scale VOR course needle deflection-meaning he is off course by 10 degrees or more-I think that pilot may be lost. Once that happens, the primary objective is to get an on-course indication; however, double the angle off the bow is not the tool to use.
Course tracking is the principal heading-control challenge for VFR pilots. If the airplane drifts off course, start a course-bracketing maneuver by turning 20 degrees into the wind. If strong winds exist or you've drifted well off course before noticing the deviation, another 20-degree turn may be required to intercept the course. When you are back on course, take out half of the initial re-intercept heading and continue the bracketing maneuver. With only two or three heading changes, you will nail your wind correction angle to within 5 degrees of what is required to track the course centerline.
It's important to remember that you don't want to wait until you've crossed through your course before turning to the course heading. Especially close to the VOR station, it's important to lead on-course turns. Many instructors recommend that when the indicator needle has traveled halfway between its original deflection point and the on-course indication, it's time to start turning back toward an on-course heading. In other words, if the needle is deflected four dots, 8 degrees, when you first turn to intercept your course, begin the turn back toward your on-course heading when the needle reaches two dots, or 4 degrees, deflection. That way you won't fly through your course. The speed with which the needle is coming in should dictate how steeply you turn toward your course. A fast-moving needle means a steeper turn.
Instrument pilots have additional course-tracking situations to consider. If they find themselves far off course en route or prior to an intermediate instrument approach fix, it's a good idea to turn 45 degrees toward the desired course. However, if the airplane is inside an intermediate approach fix, then executing a go around or missed approach immediately would be the only advisable action. Making wild corrections on final approach is never a good idea.
Why choose a 45-degree correction angle? Because the 45-degree intercept heading is denoted on the face of most vertical compass cards-directional gyros and horizontal situation indicators-by tick marks around the instrument's face. This eliminates the need to make a mental computation, which can be distracting and result in pilot error.
Some instructors teach students to use a 30-degree intercept angle. This practice is based on the 30-degree maximum intercept rule for air traffic controllers when they vector aircraft onto a course; it does not apply to pilot-initiated intercepts. In the instrument flying world, procedure turn course intercepts-45 degrees-are proof that a 30-degree intercept is not a pilot limit.
A well-trained pilot has the discipline to get on course expeditiously and stay on course using proper tracking procedures. And you can be certain that this pilot checked the winds aloft prior to departure.
