Double-Checking the Vector

A special supplement to J. Ross Russo's article "Vectors to Final."

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Near the end of a long trip, actual IMC and perhaps flown withno autopilot, being vectored to final can be a great relief. Butthere’s a downside, too. A pilot anxious to get established onthe approach and on the ground might be lulled into allowing positionawareness to lapse at a time when he or she can least afford it.It’s all too easy to simply tune the localizer and wait for theneedle to center.

What the pilot should be doing, of course, is verifying that thecontroller’s vectors will result in an intercept far enough outsidethe final approach fix (or approach gate) to allow for a stabilizedapproach. As you fly toward the inbound, on your final vector,the angle that you’ll intercept the localizer is equal to thedifference between your vector groundtrack (not the heading) andthe localizer course. Ideally, this should be between 20 and 30degrees. Of course, you probably won’t know what the wind is doingso at best, you’ll have only a vague idea of the groundtrack.

On an ILS equipped with a LOM, the best way to monitor the interceptangle is to tune the LOM and track bearings on the ADF. To achievea 20 to 30 degree intercept (and one that’ll intersect somewhereoutside the marker) the ADF needle should be about 20 or 30 degreesoff the nose and on the opposite side as the localizer. In otherwords, if the localizer says fly left, the ADF needle should beoff the right side of the nose, and vice versa.

Since the relative bearing equals the intercept angle at the momentof interception, the ADF will give some idea of how soon the interceptwill occur. In the example shown here, the relative bearing is20 degrees, the intercept angle about 30 degrees. Ten degreesdifference; a ways to go yet. At five degrees difference, watchfor the localizer needle to come alive.

Ask for another vector if the ADF needle is on the same side asthe localizer needle (interception inside the marker) or rightoff the nose, signaling intercept at the marker. An HSI simplifiesthe intercept somewhat. The vector heading should result in thelubber line being more or less off the tip of the CDI. This willassure a reasonable intercept angle. But monitoring the ADF isstill the only way to tell where the vector will intercept thefinal course.

A sure source of confusion is to get a vector opposite the directionyou expect. This sometimes happens when you’ve been vectored overtopthe airport outbound but aren’t sure which side of the localizeryou’re on. A quick method of reorienting yourself is to imaginethe words Black-On-White written across the VOR face, with blackon the left, white on the right. If the CDI needle is on the blackside, you’re on the shaded side of the ILS feather.