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There is one topic that I never can seem to get a grip on. I'm a fairly low-time pilot with around 200 hours, possess a Private Pilot SEL rating and am now about 35 hours into my instrument training. I am comfortable with enroute procedures and can fly approaches with acceptable accuracy, but have great difficulty knowing exactly when to initiate a standard rate turn so that I intercept the localizer or airway in a smooth coordinated fashion. I either start the turn a little too late, which results in overshooting (or a steeper than standard rate turn to avoid doing so), or I start too soon and end up having to roll out sooner than I want while I wait for the CDI to center.
Thanks,
Bob Lillard
Greetings Bob:
Good question.
Course interception is often a tricky thing for most, if not all, pilots. Like a surfer in search of that perfect wave, you're not alone in your quest for the perfect course-interception technique. So hang ten (fingers, not toes) on your controls and let's take a look at the problem (and have some fun along the way).
First, here's the skinny on that perfect technique for localizer interception: it doesn't exist.
Sorry.
We'll have to assume that Plato (not Playdough the child philosopher) was wrong and there's no such thing as an ideal technique to be had. It's not as if I haven't looked for one either. The perfect course interception technique doesn't exist because there are too many variables involved.
For instance, localizer widths are not standard. A localizer's angular width varies between three and six degrees so as to provide a standard side-to-side width of approximately 700 feet at the runway threshold. Variable localizer widths imply different degrees of localizer needle sensitivity. This means there's no way to standardize a precise time or place to turn or begin turning based on your distance from the outer marker.
Additionally, when a controller says that you're a certain distance from the outer marker, he or she is eyeballing this distance on the radar screen. Your actual distance may vary depending on several factors: how clean the controller's glasses are (if he's wearing his glasses at all), how many times he's rubbed his eyes or the degree of magnification resulting from that lens-like coffee puddle on his radar screen. I jest a bit, but you see what I mean, don't you?
And, just in case you think there's still hope for that perfect technique, there's one more variable that sabotages the idea. Wind! Wind changes your groundspeed, affecting the speed at which you approach the localizer centerline.
In order to make an interception technique work, you'd need to use it on the same localizer, under no wind conditions, talking to the same controller, who's wearing the same set of glasses while drinking the same cup of coffee. All of which seems about as likely as an OSHA inspector spending a relaxing and peaceful night aboard the Mir space station. So much for that, eh?
But do not despair. There's still hope. Even without the perfect technique, you still have control of the most important variable influencing your closure rate with the localizer.
Care to guess what it is?
It's your bank angle.
If you vary the bank angle in response to the speed at which the localizer (or VOR) needle moves, you'll have better control over course interception. Yet, instrument pilots are taught to vary their bank angle only as necessary to make a standard rate turn. You said so yourself when you stated, "but have great difficulty knowing exactly when to initiate a standard rate turn so that I intercept the localizer or airway in a smooth coordinated fashion."
Why are instrument pilots taught to make all turns at a standard rate?
There are several reasons.
First, it's a matter of convention. Turn and slip indicators (Figure 2) were around long before attitude indicators. These instruments provide rate of turn and slip/skid information only; bank information isn't provided. With the turn needle on the index mark (also known as the dog house) turns are made at a standard rate of 3 degrees per second. This was the only means of bank control that early instrument pilots had. In other words, these early pilots couldn't directly tell how steep their bank was, nor do I suspect they cared all that much. All they were concerned about was banking the airplane until it turned at 3 degrees per second, no more, no less.
Turning at a standard rate was especially important because early aviators frequently had to rely on their magnetic compass for heading control (geesh! Imagine that!). Therefore, at 3 degrees per second, they could accurately estimate when to roll out of a turn (e.g., 30 seconds for a 90 degree turn), instead of attempting to read a wobbly and error-prone compass.
Therefore, turning at a standard rate is essentially a carryover from the early days of instrument flying.
Second, standard rate turns are relatively shallow banked turns, making it less likely that a pilot will experience control difficulties (vertigo, overbanking, etc.). Of course, the bank required for a standard rate turn varies with airspeed. The higher your TAS, the greater the bank necessary to turn at a standard rate. At 90 knots you need only about 14 degrees of bank for a standard rate turn; at 120 knots, 17 degrees of bank; and at 160 knots, you still only need 21 degrees of bank to turn at standard rate.
Finally, making turns at a standard rate requires you to look at the turn coordinator. But who says you always need to look at your turn coordinator when flying on instruments? After all, in cruise flight at 120 knots, can't you roll into a 17-degree bank on the attitude indicator and accomplish the same thing?
Yes, you can.
Since all of today's modern airplanes have attitude and heading indicators, standard rate turns are a bit antiquated. Most of my airline and corporate pilot buddies don't think in terms of standard rate turns. They simply bank the airplane 20 to 30 degrees on the attitude indicator. Nevertheless, they still use the turn coordinator as a means of confirming that their attitude indicator is working properly. Which is a good reason to keep making standard rate turns since it requires you to include the turn coordinator in your scan. After all, When both the attitude indicator and turn coordinator show rolling/banking motion in the same direction, you know that that both instruments are probably working correctly. Hey! There's no sense having a pilot test his triple bypass by having an attitude indicator failure go unrecognized under instrument conditions.
The question is, "Can you make turns while on an IFR flight plan at a rate greater than standard?"
The answer is, "Of course you can!"
There's no rule or law of which I'm aware that says all turns must be standard rate turns (although it's wise to do so unless you have a good reason not to and I'll show you a good reason shortly).
I consulted my trusty Summit Aviation CD and found a few references to standard rate turn limitations that might interest you.
Page 70 of the FAA's Instrument Flying Handbook says:
"In any case, limit your bank corrections to a bank angle no greater than that required for a standard rate turn. Use of larger bank angles requires a very high level of proficiency, and normally results in overcontrolling and erratic bank control."
As you see, this is a good conservative recommendation but it doesn't specifically prohibit you from making turns at a bank slightly above that required for standard rate. There is also a standard rate turn recommendation for entering and flying a holding pattern. And the FAA's Instrument Pilot Practical Test Standards does require an applicant to make standard rate turns during the flight test. (Therefore, none of the following recommendations apply until after you receive the instrument rating. Other than that, you're on your own.)
So what's the point to all of this?
After, and only after, you acquire your instrument rating, here's what you can do to help with localizer and airway interception.
During a vector to the localizer, if the needle moves quickly toward the center, make a turn slightly above standard rate. In this case, I might not even look at the turn coordinator. I might focus my attention on the attitude indicator and use 20 degrees of bank. Remember, we're not talking about a steep turn here. Nor are we talking about making a turn at a bank that will cause an airplane to overbank and fall out of the sky.
Additionally, you're only turning a short distance to intercept the localizer. While vertigo is always a problem when flying on instruments, I can't see how you'd have any appreciable increase in the chance of getting vertigo by turning this distance at a slightly steeper bank. I will, however, let you be the judge of the bank angle you feel comfortable with. (Note: There's seldom any reason to exceed 30 degrees of bank under instrument conditions. In fact, pilots for many airlines are limited to a maximum 30 degree bank under normal conditions.)
Why is it so important to get on the localizer (or other course) and not dally during intercept? The sooner you're established on the localizer, the sooner you can get all your prelanding chores squared away. This means you're less likely to be rushed and, as a consequence, forget something.
Nevertheless, suppose the needle swoops from one side of the VOR to the next so quickly that you're afraid it could break off and stab someone. What do you do now?
Nothing!
That's right, nothing.
Let it go. Make a standard rate turn and reintercept it from the other side. There's no reason for super steep banks just to capture a rapidly moving needle.
Finally, suppose the needle moves toward the center slowly when intercepting the localizer? First, most vectors to the localizer occur at a 20 to 30 degree angle. It's possible that a strong opposing wind might reduce your groundspeed sufficiently so that your localizer closure rate is very, very slow. I've been on approaches under strong wind conditions where a 20-degree intercept took my students inside the outer marker before intercepting the localizer. Since you could be vectored to within a mile of the outer marker, a strong opposing wind could make interception seem as fast paced as a poetry reading.
We must remember that controllers can't tell the direction your airplane points (your heading) on their radar screen. They observe ground track only. Therefore, a controller may assign a 10 or 20 degree intercept without a sense of how the wind might affect your airplane. So if the rate of course closure is too slow, ask the controller for a different intercept heading. In many cases, if the needle moves too slow, professionals just take an additional 10-degree bite at the course.
Shouldn't you ask the controller for permission before changing headings, even when you've been cleared for the approach? Sure. But let's be practical here. Things are happening pretty fast when you receive an approach clearance. The controller may be busy talking to someone else. I'm sure he'd rather have you intercept the approach course rather than make a missed approach. Remember, your job is to get on the localizer (or other approach course) when you're cleared for the approach. So, if your intercept heading isn't working, take an additional 10 degree cut and inform the controller if and when you have time.
I hope this helps.
For more information on this subject, see "Needle Mania! How To Use The VOR" and "Insights: Old-Fashioned Intercepts."
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