I have recently started working towards my CFI certificate. On my first ground session with my instructor, we discussed airspace. I began with the usual rundown: listing requirements-to-enter, cloud-and-visibility minimums, etc. He then asked, “Jason, tell me why, when flying over Class C airspace we need Mode C, but underneath the shelf we don’t need it?” Or “Why does the Mode C veil of Class B extend to 30 nautical miles?” I thought for a minute and discovered that I really had no idea why those rules existed.
Aviation is certainly full of “whats.” We have our checklists for each phase of flight and mnemonics to memorize important bits of information. We memorize the whats of V-speeds, airspace requirements, emergency procedures, aircraft performance figures, weather product acronyms and more. Of course this is no different from a business asking for facts and figures so they know what is happening or has happened in their world. But the “whats” certainly don’t tell the whole story.
As if taking a technique out of the Aviation Instructor’s Handbook, many more “whys” came through during that lesson, followed but my best deer-in-the-headlights look and lots of “well…huh…umm?” Where did all these “why” questions come from? I began to feel like my instructor was one of those kids visiting my planetarium who just kept asking, “Why? Why? Why? Mr. Archer!”
According to the FOI (Fundamentals of Instruction: yes, I have read the book and I actually enjoyed it…what is wrong with me?), “why” is an open-ended question designed to “encourage full, meaningful answers using the student’s own knowledge and perceptions.” This is as opposed to closed-ended questions that generally lead to short or single-word answers, the kind you get when you ask a teenager, “How was your day?”
“Fine!”
Let’s take a look at some aviation “whats and whys.”
Here at my home airport in Hartford, Connecticut (KHFD) we have a VOR-A approach. What does the Alpha mean? Well, it means that this approach procedure is a circling-only approach. No landing minimums are published, because the final approach course alignment exceeds 30 degrees from the runway heading. Why, you ask? A straight-in is not possible because of an obstacle and/or the descent gradient is more than 400 feet/nm between the FAF and the TCH because of an obstacle. I’ve always just accepted this and understood what it means, but it never made sense, as there are no obstacles on this approach. KHFD also has an LDA RWY 2 with a straight-in, as well as the RNAV RWY 2, also a straight-in. I know how to fly both these approaches as I practice them regularly. I never asked why till I learned more about the history of the field.
Turns out KHFD had a different runway layout many years ago. Today we have runways 02/20 and 11/29 but one time there was a runway 33. Check out the VOR-A approach plate and you will see that the approach course is 334 degrees, straight at Taxiway W, formerly known as Runway 33. It also now makes sense why that taxiway is the only one set at an odd angle compared to taxiways C, D and H. The VOR-A Approach is a straight-in to what is now an ex-runway.
Speaking of VORs, ever wonder why jet routes stop at FL450? Below 18,000 feet we call them victor airways. VORs define the jet routes and victor airways. Think about the VOR signal, it is line of sight. Above FL450 a VOR signal can be seen farther than where the signal is guaranteed. In short, signals can cross. Not a very reliable way to navigate.
Up at these altitudes you’ll set your altimeter to 29.92. In fact, everyone sets their altimeters to 29.92. At least we hope so. Why? Because it says so in AIM, Chapter 7, Section 2? Sure, but there’s a better reason. Airplanes above 18,000 feet are moving fast. Not your Cessna 172 fast but close-to-Mach speeds fast, thus they are covering a lot of ground in a short time.
We low-and-slow pilots are told to adjust the altimeter to a station within 100 miles of us. In the average trip we’ll reset it just a few times. And, if we forget (don’t forget) but if we did, at 100 miles per hour we’d have more time to see that traffic we’re about to pass too close to. But at 400-plus miles per hour, we’d have to do that every 15 minutes. By having everyone at 29.92, it puts all aircraft on the same altitude reference. That is a very good “why.”
Let’s come back down in altitude. You’re on the runway, you gently and smoothly push the throttle forward, accelerate, pull back and up you go. Life is just grand. What is one of the things you do? Push that right rudder in. How do you do it? Push a little with the right foot. Good, but why? You might say it is to keep that ball centered, which is true. But just as important is the why, and that why is “due to the left hand turning tendencies of the aircraft.” You see, it’s all aerodynamics. Now don’t go running for the hills just yet. Why you push that right “foot rest” in, is to counter the three forces of P-factor, torque and the spiral slipstream that act together to turn the airplane left. How and why do these happen?
As seen from the pilot’s seat, the propeller creates a clockwise corkscrew of air that hits the rudder on the left side, thus yawing the airplane to the right. This is called spiraling slipstream. The effect of torque is created by the engine spinning the propeller. Due to Newton’s Third Law, that creates roll force in the opposite direction of the propeller, thus rolling the airplane to the left. Now wait a minute? How does right rudder which controls the yaw axis of the airplane deal with torque, which is about the rolling axis of the airplane?
Well, to correct the counter-clockwise roll created by torque you use opposite aileron. So the left aileron goes down to create more lift, thus rolling the airplane clockwise. By creating more lift on the left, you also create more drag, thus yawing the airplane to the left. So really, this correction with the ailerons is then further corrected with right rudder. Now, that wasn’t so bad was it? Just be thankful you’re not in a P-51 that had so much torque that many a pilot would flip the airplane even before they left the ground.
Finally, lets add P-factor, created by the descending propeller blade on the right creating more forward thrust than the ascending blade on the left. This yaws the airplane to the left. Why does it create more thrust on the right than on the left you ask? Well, at our nose-up attitude in a climb, the descending blade has a higher angle of attack than the ascending blade on the left. More angle of attack equals more airflow which equals more thrust.
Notice I never mentioned gyroscopic precession as one of the left turning tendencies. Why you ask? Gyroscopic precession is a left turning tendency during take off if you are flying a tailwheel airplane. It is felt when the tail rises, moving the nose to a level pitch attitude. During that transition you’ll feel the aircraft yaw to the left. In our tricycle gear airplane this isn’t a factor as the nose is already level. It is actually a right turning tendency, however, as we pitch up to climb.
Everything that goes up must also come down. So have you ever noticed that in a descent you need a little left rudder? The why of this is simple. This same force, p-factor can tend to move the airplane to the right when in a descent. Here, the ascending blade has a higher angle of attack. This is particularly noticeable on that descent from the FAP when your power is pulled back.
Now that we are up in the air, have you ever wondered why 1,000 feet AGL was chosen as our minimum ceiling for VFR in controlled airspace? The what is that we need three statute miles of visibility 1,000 feet above clouds, 500 feet below and 2,000 feet horizontal from said clouds. Well, recall that we need at least 500 feet from any obstacles and if we add the 500 feet below the clouds (so we don’t run into IFR traffic) then we get 1,000 feet. There you go!
There is a lot to learn, remember and keep fresh to be a good pilot. Becoming a CFI should certainly push one’s level of understanding to a correlative level of knowledge and will undoubtedly show any weaknesses, or at least it should. Rick Mahoney Jr. (CFI, AGI, ME) with Premier Flight Center says, “As instructors, we owe it to our clients to be ready for all their questions, to help and guide them. We cannot develop a higher order of thinking skills in our clients – never mind push them higher through the levels of knowledge to correlation - without getting them to ask ‘why.’ If our own inquisitive sense of intellectual curiosity and inquiry ultimately allows us to grow in our instructional ability to teach our clients, we are duty-bound to pass along the ability to our clients the insatiable desire to question and develop theirs. Without that ability, where does critical thinking and scenario based training have a place in the future of flight training when we’ve misplaced the ‘why?’” I couldn’t agree more.
Jason T. Archer holds AGI and commercial certificates with instrument rating and tail wheel endorsement. He is an active FAASTeam Representative and a fixture at his home base of KHFD. He can be contacted at info@thedaedalist.com
