July 1, 1996 Do the PT Right

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by	Joseph M. Foresto
	This article originally appeared in the June 1996 issue of IFR MAGAZINE and is reprinted here by permission of Belvoir Publications.

Cessna Three Four Uniform, cleared direct to the Lost at or above 3000 feet, cleared for the VOR 24 approach at Podunk Muni, report the procedure turn inbound.

The above is a routine clearance that's probably issued a hundred times a day by various ATC facilities. You're instrument rated, so we'll assume if you hear a clearance like this, you know it's required. But what's the best way to actually fly the turn? There's no simple answer. It falls into the category of elective technique.

Although there may be many "right" ways to do a PT, there are certainly some wrong ways, too. No matter how you fly the turn, the critical thing to remember is to do it in a way that keeps you well within the obstacle protected area while still giving you enough time and distance to line up on the course outside the final approach fix.

Think Speed

The drawings at right depict the typical protected areas for both a standard, barbed-procedure turn and for a holding-pattern-in-lieu of a procedure turn. As you can see, there's plenty of safe maneuvering room around both types...unless you happen to be flying a very fast airplane, fast being up to the 250-knot-below-10,000 feet-MSL limit. That's not to say there's not enough room for a fast mover — say a biz jet — to make the course reversal, it's just that there's less margin if you get careless.

On Jepp charts, the procedure turn barb is to scale in the plan view. That means if the profile view says "10 NM from NDB," the outer edge of the barb is at the 10-mile limit. If the PT limit is only five miles — as it is if the approach is limited to Cat A airplanes — the barb is obviously much shorter. On NOS charts, the plan view has a 10-mile distance circle and virtually all of the barbed PTs extend to the inside edge of this circle. On both charting systems, the holding-pattern-in-lieu of PT reflects no particular scale; it's just a graphic representation. The obstacle clearance area we've drawn here represents a typical application for a holding-pattern-in-lieu of: the number 4 holding pattern template.

The thing to worry about here is approaching the PT fix at a relatively high airspeed and perhaps with a stiff tailwind. In a 100-knot Cherokee, unless you're asleep at the yoke, you'll probably have plenty of time to get yourself turned around without busting even the relatively small protected area of a holding pattern-in-lieu of PT. But if you're driving a Lear into the very same airport, the protected area is the same size as it is for the Cherokee.

You could be doing 300 knots over the ground; five miles a minute. At 100-knots, the turn radius of the Cherokee is about 1/4-mile. For the Lear, it could be more than a mile-and-a-half, even without taking into account the tailwind, which could push the turn toward the edge of the protected area.

Most of the time, these speed factors probably won't matter much. But in extreme conditions — such as the 80-knot low-level winds described in the accident analysis on page 6 of this issue — they could be a factor. If you're watching your groundspeed on loran or GPS, you should have a good idea of windspeed at altitude; plan accordingly.

For flyability, the turn should be planned so that you're established on the inbound course, with a centered needle, or nearly so, at least two miles outside the FAF. As a matter of personal preference, you may want to stretch that to three miles and that's fine. Just be mindful of the wind and make sure you stay within the published PT limit.

Which Way?

In your instrument training, your instructor may have insisted that you fly a standard barbed PT just as it's depicted. Nothing wrong with that. But you don't have to do it that way. Both the FAA's Instrument Flying Handbook and the AIM say that "the point at which the turn may be commenced and the type and rate of turn is left to the discretion of the pilot." Besides the standard 45-180, you can also fly a 90-270 or what some pilots call the 40-second turn, which consists of an abbreviated 45-degree outbound turn to compensate for the effects of a tailwind.

You can even execute a 45-degree turn from the outbound leg, followed by a 180-degree turn toward the airport to intercept the inbound. Just make sure all of this maneuvering is done on the protected side of the course, that is, where the barb is depicted.

If you're flying a holding-pattern-in-lieu of a PT, the AIM recommendation is to use a standard holding pattern entry. Remember, the protected airspace is smaller, so keep it as tight as practical. The one-minute posted on most of these refers to a one-minute inbound leg, with timing starting as soon as you're wings level on the inbound course, same as a standard hold. However you choose to enter — standard method or something else — to maximize your obstacle protection, do as much of your maneuvering in or as close to the depicted holding pattern as possible. Minimize excursions into the non-holding side of the course.

There are a few teardrop-type procedure turns here and there in the U.S. These must be flown exactly as depicted; no improvisation allowed. Most have positive course guidance — say a VOR radial — for the outbound leg, then a DR inbound turn to pick up the inbound course, again, defined by positive course guidance.

There are lots of tricks to fly a PT that will put you on the inbound two miles outside the FAF. One simple method is to think back to your high school geometry days. Remember the formula for calculating the hypotenuse (longest leg) of a right-angle triangle? It's a² + b² = c². In this case, c is the length of our outbound PT leg, while a is that two-mile distance we want when we roll out on the inbound course.

Doing the math using two-mile legs, the hypotenuse — outbound leg — is 2.8 miles. Round it off to three miles to make things easy. Now, instead of guessing at timing, for the outbound procedure turn, turn to a groundtrack that's 45 degrees off outbound course, then use your actual groundspeed to determine how long to fly outbound. Rule of thumb: At 120 knots groundspeed, you're going two miles per minute so use 90 seconds; at 180 knots, a minute will do; at 90 knots, two minutes.

When you turn inbound, your actual intercept will actually be a little inside of two miles from the FAF, depending on the wind, but it'll be close enough. If you want three miles from the FAF, fly the outbound PT leg for an additional mile or use 30-degrees off the outbound, rather than 45 degrees.

VOR, Loran and GPS

On a VOR approach with procedure turn, you can use the CDI scale to estimate your distance from the course. As a rough rule of thumb, your distance offset from a VOR course is equal to 200 feet per dot per mile. So, let's say you're on the outbound leg, the 360-degree radial. You eyeball the 45-degree outbound procedure turn and watch the CDI needle, checking your DME distance from the VOR, which happens to be, say, 10 miles. At four dots deflection, you'd be 8000 feet or 1.3 miles off the course. Still well within the protected area. (On a VOR, four-dot deflection at 12.5 miles would still be well within the two-mile offset we offered as a good gouge.)

If you have loran or GPS — and these days, who doesn't? — how can it help on the PT? One quick-and-dirty method is to just pass over the fix where the PT starts and then use the GPS or loran to fly a groundtrack 45-degrees (or whatever) off the outbound leg. Thus, if the outbound is 180-degrees, turn to a groundtrack of 135 degrees for your outbound and time the leg for a three mile segment. It's hard to get much more accurate than this.

Some pilots plug in the entire approach as a route and although that may be too involved to do in the air, it can be done ahead of time. In this case, use the receiver's offset waypoint capability to place a point in space where you want to terminate the outbound PT leg. If you want to get really elaborate, you can also put a waypoint on the inbound course, where the PT intercepts it, two miles outside the FAF. To keep things legal and safe, make sure the GPS or loran guidance squares up reasonably with your dead reckoning.

Keeping in mind the purpose of the course reversal, I run a mental checklist on these items: (1) Set up approach configuration and airspeed before reaching the fix where the PT begins, including flaps as appropriate. (2) After crossing the fix, turn outbound on the protected side to yield a 45-degree groundtrack and (3) apply the speed factor to yield a three-mile outbound leg or whatever will have you intercept the inbound course two miles outside the FAF.

Finally — and this is critical — what is the wind direction and speed and what's it doing to your groundspeed? In a fast airplane, this could make all the difference in the world. Don't lose track of it.