![]() Moving clockwise on the arc, your intercept with the arc is less than 90 degrees, necessitating a later start to your turn to roll out cleanly on course.Ĭounter-clockwise on the arc, the turn is well over 90 degrees and you’d want to start early. The arc is off the Hutchinson VOR and makes two different angles on the localizer. The smaller the arc and the faster your groundspeed, the more lead you’ll need.ĭo a few of these and you get the hang of when to start a turn, but it gets more complicated when the inbound course isn’t lined up with the arc, as is the case with the ILS or LOC Rwy 13 at Hutchinson, Kan. You lead the turn by some amount depending on how fast you’re closing on the course. Of course, you don’t wait until you reach that inbound radial to start your turn because you want to turn 90 degrees and roll out on the inbound course. When the arc and the final approach course are determined by the same VOR, the intercept angle is always 90 degrees, because the arc is a circle around the VOR and the inbound course to the VOR is a radius of the same circle. Now arcs get transcribed into curving, magenta courses on our GPSs that we can just follow if we get a clearance to actually join an arc and fly the approach. This is the old “turn 10, tune 10” technique many of us learned. Now GPS and more ubiquitous radar coverage have made their use less common.Ī typical arc uses a VOR (or sometimes NDB/DME) on the airport property for swinging the pilot around in a clean curve to intercept the final approach course. They were once a common way to save the controller some vectoring time and put navigation into a pilot’s hands. Subtle suggestion fits the bill when it comes to lead radials off DME arcs.ĭME arcs are one of the skills resigned to the atrophy basket for many of us. Some directions are bold and unmistakable others are easy to miss. Maybe it’s because the ones who don’t follow directions in IMC aren’t around for long. Maybe it’s because 49 times out of 50 what’s asked is what they expected anyway, so their inner know-it-all teenagers are smugly satisfied. How you take the hint depends on both the approach in question and your relative velocity.ĭespite the quips about aviator egos barely fitting inside the cockpits that carry them, pilots have a high tolerance for following directions. ![]() These crossing points on the arc are more helpful suggestions than hard rules. ![]()
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