On Instruments: Vector-to-final insights

This is great news—you’re being vectored to the final approach course. ATC is setting you up for a course interception and you don’t have to fly a full-blown procedure, complete with a course reversal via a procedure turn or—gasp!—a swing around a holding pattern. In fact, FAR Part 91.175 (j) prohibits pilots from making procedure turns when being vectored to a final approach fix or final approach course—unless ATC requests one.

So you just fly the heading until the localizer needle comes off the peg, then turn to intercept it, wait for the glideslope needle to come alive, wait until it reaches one dot high on your course deviation indicator (CDI), make sure the airplane’s configuration and power are set correctly, and fly down final approach.

What could be easier? ATC is basically doing the navigation for you. But even so, issues can crop up. Controllers often use the concept of an “approach gate” when vectoring airplanes for instrument approaches. The “gate” is an imaginary location—you won’t see it on an approach plate—that’s at least one mile from the final approach fix (FAF) and at least five miles from the landing runway threshold. Before any arriving aircraft reaches the gate, controllers issue vectors that will result in final approach course interception angles of no more than 20 degrees. And the intercept must happen at least two nautical miles outside the approach gate.

Sounds good, right? Your intercept angle will be a shallow one, the CDI needle should come in slowly, and you’ll be far enough away from the FAF that you should have plenty of time to set up the airplane for the trip down final.

But has anyone out there been given a vector that ends up with an intercept angle of 50, 60, or even 90 degrees? I sure have. This is bad news because it’s easy to blow right through the localizer or other navaid’s final approach course guidance. The CDI swings from one side to the other and now you have to bank—steeply—back to re-intercept the final approach course. Suddenly it’s a rush to the FAF, and maybe even a rush to adjust power and flaps, and lower the landing gear in a retractable-gear airplane. Not exactly ideal for a stabilized approach—especially if the arrival weather features low ceilings and visibilities.

That’s not supposed to happen, but controllers aren’t perfect. And when the weather is down at a busy airport, more airplanes must be sequenced and their workload shoots up.

But wait. There are times when ATC can give you a late turn onto the final approach course and, yes, with intercept angles greater than 20 degrees. If the airport’s ceiling is at least 500 feet above the minimum vectoring altitude (MVA) or other minimum IFR altitude, and the visibility is three statute miles or more, then you can be vectored to final at minimal distances from the approach gate. This could be as close as five nautical miles from the runway. For all practical purposes, this could be considered a maneuver consistent with a visual approach, where you may be asked to follow an airplane on approach ahead of you.

One way to get turned onto final inside the approach gate—but no closer than the FAF—is to come out and request it. Common sense dictates that the weather had better be decent visual meteorological conditions (VMC: a 1,000-foot ceiling and three statute miles’ visibility) for this move. Otherwise, if you lose sight of the airport—or, much worse, enter clouds—you’ll have to fess up and be sequenced and cleared for another approach.

So yes, vectors to final are wonderful things. But don’t get complacent. Bad things can happen while being vectored, as we’ve seen. All the more reason to stay ahead of the airplane and make sure your situational awareness is on high alert.

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