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One of the more interesting things to do on practical tests is to explore beyond a pilot certificate (or rating) applicant’s rote level of learning. As a matter of fact, one of the things examiners are required to do is evaluate an applicant’s aeronautical knowledge, in as practical a setting as we are able to create. Yes, I recognize the artificiality of a practical test. All of us know that the Practical Test Standards are certainly not everything one needs to know to be a pilot, and yet that is all so many instructors teach their students. The rating mills out there — we all know who they are — certainly can’t go beyond the rote level in the time they allow to complete a certificate or rating.
I certainly try to look beyond rote learning. I expect the application level during the ground portion of the test, the correlation level on the flight (look in the Aviation Instructor’s Handbook to define those terms), and the questions I ask reflect this by being somewhat open-ended. Remember, too, that I’m not your friendly flight instructor during the test — I’m not allowed to help you, so whatever happens, be it good or bad … it really is your fault.
Then there’s the Flight Instructor practical test. I’m here to tell you that rote memory absolutely won’t cut it, folks.
Let’s look at one topic that, according to NTSB statistics, on the average causes at least one fatal accident each year and one non-fatal accident each month: wake turbulence. It is a subject the FAA and Practical Test Standards require me to ask about on every practical test. It has been around since the dawn of flight, which is to say since the earth has had an atmosphere. So just why is it, do you suppose, that wake turbulence continues to cause so many problems?
When I ask an applicant, “How do you avoid wake turbulence? What causes it?” — the responses are predictable: “Always fly above the flight path of the airplane ahead. Land after the heavy airplane’s touchdown point and take off before its rotation point.” End of answer. Is this really enough, though, to demonstrate whether the applicant has an understanding of how wake turbulence might affect his flight? What about other scenarios where wake turbulence is a factor?
Many airports have parallel runways. Where both general aviation and airline, sometimes military, traffic mix regularly, often ATC will use one runway for the airline (or military) traffic and the other for the GA traffic. Orange County in southern California, the 19 runways at Las Vegas-McCarran and Phoenix Sky Harbor are like this. Where the runway separation is less than 2,500 feet, disaster awaits the unsuspecting pilot who isn’t aware of any crosswind, or even calm winds. Just think about having a vortex encounter about 50 to 100 feet above the runway ...
Some airports have intersecting runways, one of which may be used for airline departures and the other for arrivals. San Francisco International and Yuma, Arizona, are two that have this configuration, as does Las Vegas-McCarran when the winds permit using the east-west and north-south runway complexes. In general, this is not as dangerous a situation. An in-flight encounter when the flight paths cross at something near 90° may result in some good up and down excursions, but usually do not result in an upset. A couple of years ago, my Cessna 180 and I had an encounter with an MD-11 at Yuma that was startling, but produced no long-term effects. The airliner wasn’t all that high; I just thought I could be above his flight path!
San Diego International Airport (Lindbergh Field) has a bit of an unusual situation on runway 27 (besides the approach, I mean, for you kerosene-burning folks). The landing threshold is displaced about 2,000 feet or so down the runway, but all takeoffs start from the blast fence at the end for noise abatement reasons. Consider this: here you are, waiting for takeoff, when an airliner approaches and lands, probably another 1,000 feet past the threshold. The tower, trying to be helpful, clears you first into position and then for takeoff. There are three other airliners waiting for you to go, and two or three on the approach. How do you avoid that fabled E-ticket ride once your wheels are off the ground? You have the option of climbing through those descending vortices or ... just what do you do? You better have thought about it before you call the tower!
The unfortunately short-lived FAA Aviation Safety Journal, Vol. 3, No. 1, back in 1993 had an excellent article by Dr. Robert E. Machol, complete with vivid photographs, on this very subject. It introduced some of the research going on until that time and discussed some topics not generally thought about in conjunction with wake turbulence. For example, what effect does atmospheric stability have on vortex strength and duration? It turns out that for both stable and unstable air, vortices tend to diminish rapidly. In neutrally stable air, however, in his words, “…vortices seem to last forever.” He goes on to say that “…this is a comparatively recent discovery that makes much of the data from years past less useful because we do not know what the lapse rate was at the time the data were taken.”
Do I really expect a private pilot applicant to be able to explain what is going on here, with all the possible scenarios? Well, probably not in this detail, but think about it for a minute. Does the wake turbulence care about the pilot certificate held by the person with their hands on the handlebars of that following aircraft? Who’s responsible to avoid it? The AIM says, “… the flight disciplines necessary to ensure vortex avoidance … must be exercised by the pilot.”
This is certainly not an exhaustive discussion of wake turbulence, but my editor just won’t let me fill the whole issue with just one discussion topic. There are other situations — helicopters, crosswind and tailwind effects — worthy of study. Look in the AIM, section 7-3, Advisory Circular 90-23 (whatever the current revision), and other places. Don’t become a statistic.
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Aviation Training