Teaching Landings - More than an Issue of Stability

Bushpilot048

Newbie
Oct 22, 2009
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Pilot Perception and Landing an airplane.
Over the years, I’ve read dozens of articles describing ‘how to land an airplane’. All have similar issues in common and are right on spec with description of what’s happening aerodynamically and mechanically when going through the process of landing. Stabilizing the airplane in glide, airspeed control, altitude/glide rate adjustments with power, pitch control , directional control with rudders, aileron-rudder coordination to limit drift, etc. The list and approaches (no pun intended) go on and on. However, one element of landing description seems to be missing from the articles that I’ve read, and that’s ‘pilot perception’ when going through the landing process. I have yet to find an article dealing with related physical/mechanical feelings, visual contact and mental perceptions a pilot experiences when landing an airplane. The question is, what does the student ‘see’ and ‘feel’ during landing.

Before I launch into my thesis on this, I do want to point out that I am not trying to refute or challenge any of the articles that I’ve read. All are spec-perfect in what they are trying to say and I encourage all readers to learn from what’s being said. I want to emphasize that I am trying to add to the knowledge base an element of consideration that I believe has not been treated before in articles dealing with landings. With this, my ultimate focus is simply to add to the knowledge field of teaching and to share what I am doing to teach safe, consistent landings to my students. You can agree or disagree, but at least think about the issue.
One issue that comes into dominant play during landing is airplane stability. This is commonly taught to all students by all instructors and really is not the major point that I wish to make in this note. Setting up the airplane into a stabilized glide is primary for getting to the threshold. The airplane on final should feel stable under and around the pilot. Once set, the plane requires only light control pressures in order to maintain the stable glide. Airspeed, glide rate, vertical speed, yaw control are much more easily controlled if the airplane is stable. OK, nothing new; so, what’s my point. My point is teaching ‘instability’ … That is, after passing over the threshold, reducing power and rotating into the flair, student perceptions and feel for the landing are quite different than when in the power controlled descent.

I have found that during the descent to landing, part of the descent is in a stable airplane while in another part (the landing flair) the airplane is unstable. Students typically learn to apply a stabilized, ‘power-controlled’ glide down to the runway threshold in a relatively short period of instructional time, but the problem comes when the student transitions into the flair. Now the airplane is unstable and the descent becomes a ‘pilot-controlled’ descent. What does the student perceive at this point of the descent? Visualize, the power is reduced, back-pressure is applied to the yoke and the airplane pitch is raised to level flight over the runway. The student is typically instructed at this point to control several aerodynamic factors simultaneously while maintaining directional control and rate of descent to touchdown. This is where student / pilot visual perception is critical and – in my opinion – often misdirected.

The first issue that the student (and instructor) need to realize is, once the airplane has entered the landing flair it is no longer stable. At this point, two issues need to be taken into account simultaneously as far as descents go, and these are (1) rate of ground closure perceived and(2) visual reference of the cowling/nose of the airplane to the horizon of the runway. As the pilot approaches the ground during a glide, there is a sensation of ‘Ground-Rush’ indicated by surroundings getting larger very quickly. As the student reaches the runway threshold, the airplane is brought into level flight to ‘slow’ the ground-rush effect and power reduced. At this point, eye contact typically transitions down the runway. I emphasize raising the cowling to the ‘Horizon-of-the-Runway’. While in the flair, I have found that by telling the student to be sensitive to two things, their learning curve on landings increases very rapidly. I tell the student to watch and be sensitive to both ground closure rate (or, ground rush effect) and position of cowling relative to horizon of the runway. Apply backpressure to the yoke in tempo with ground closure, but not so fast as to let the cowling pass through the horizon of the runway. This technique requires the student to be aware of and visually control – by application of back-pressure on yoke - two visual issues outside the airplane simultaneously; ‘ground-rush’ and ‘cowling position’ during descent to touchdown. If the cowling goes through the horizon, release just enough backpressure to bring the nose back to the runway horizon. If the cowling is pulled through the horizon of the runway, the airplane will stall high every time and result in a hard landing. Also, once in the landing flair and flying level with cowling position set, the pilot/student must maintain sufficient backpressure to control the loss of longitudinal stability. To clairify, let’s do a mental experiment (and I do emphasize ‘mental’): Think what would happen if - during the landing flair - your student suddenly and completely releases the back-pressure on the yoke control? If the airplane isn't on the ground already, the plane would instantly dive into the ground most likely resulting in extensive damage to the airplane and possibly pilots. Of course, this is prevented by pilot control of the descent during the landing flair by applying just enough back-pressure to the yoke in tempo with the ground closure rate until the airplane makes contact at touchdown. Of course, one is not finished flying at this point. The pilot should maintain the amount of applied back-pressure used when touching down so as not to allow the nose to drop rapidly causing a potential ‘porpoise’ or ‘bounce’ effect during the roll-out .
I did not emphasize many other aspects of the landing such as drift control and slips and I certainly do not want to minimize the importance of this aspect of any landing. But this, in context, is a method of teaching landings that I’ve used for many years and found to be neglected in articles and discussions on landings. I believe it is most important to developing student perspective and perception during this phase of flight training. By dividing the landing process into these two separate issues, the student seems to quickly and efficiently develop self confidence and consistency in safely landing an airplane.
 
Just a technical note. You mention that the airplane is "unstable" in the landing flair several times. Airplane stability/instability is a specific issue having to do with whether or not the airplane tends to return to a given attitude after a force momentarily acts on it. All civilian airplanes are required to be stable if operated within the namufacturers limitations. I assume that you really mean that the airplane is not in steady state flight during the flair.

Jim
 
Just a technical note. You mention that the airplane is "unstable" in the landing flair several times. Airplane stability/instability is a specific issue having to do with whether or not the airplane tends to return to a given attitude after a force momentarily acts on it. All civilian airplanes are required to be stable if operated within the manufacturers limitations. I assume that you really mean that the airplane is not in steady state flight during the flair.

Jim

...you really mean that the airplane is not in steady state flight...

"Steady State Flight"... I'm assuming you are referring to an airplane that has theoretically been trimmed into a 'hands-off' configuration requiring small flight control inputs in order to manage or control the airplane while the 'balance of forces' issue is equal to zero; i.e., unaccelerated flight.

Yes, I do mean 'not in steady state flight'... "Not in steady state flight" seems to me ( respectfully ) to be just another way of defining 'unstable'... Granted, all civilian airplanes are required to be stable if operated within the manufacturers limitations... I don't dispute this, but the landing flair after crossing the runway threshold, reduction of power, and increasing pitch attitude without changing the trim definitely qualifies as 'not in steady state flight'... The point of my note is that I've never seen and noted articles dealing with "Pilot Control Descent" when "Non-steady State Flight" configuration is required in the landing flair and touchdown procedure.

Students and pilots eventually learn to manage the landing flair and become very accomplished, safe pilots. However, in discussions with many flight instructors about their techniques of teaching the flair, there seems to be as many methods as there are students, but none approach the issue from the point of 'instability'. Always, Stability, Stability, Stability!...Without question, stability (I call it power-controlled, stabilized descent) is the absolute undisputed best method in teaching glides for landing, but this only gets the student to the threshold. After the threshold, the pilot must control the final few feet of descent with positive control inputs to control 'ground-closure-rate' and 'the longitudinal configuration' of the airplane. (This I refer to as a pilot-controlled descent.) These two issues must be perceived simultaneously through 'back-pressure application rate' relative to the ground closure rate (peripheral vision) and control of the aircraft's pitch attitude relative to the horizon of the runway. BOTH events must be simultaneously managed; i.e., one issue depends upon the other. One of my students said "It's like learning to walk and chew gum at the same time. You don't really think about the parts, you just do it in a coordinated controlled way and it works. Mainly because I can 'feel' and control the airplane's descent relative to perceived outside references."

I don't really mean to create a controversial debate on technique and aerodynamic technology. All I wanted to do is make a note on an element of teaching landings that I think is important beyond the concept of stability.
So, the next time you are in your landing flair, check what's happening... I think you'll find that you (the pilot) will be subconsciously watching and controlling together (1) ground closure rate and (2) longitudinal attitude of the airplane via an 'unconscious' (but properly applied) application of yoke back-pressure to set the airplane down smoothly and safely.

Thanks for the reply. This is what this forum is all about, an exchange of ideas to strengthen the flight instructor in their quest to teach 'everyone' to fly... Ya'll have a great day! ...jp

PS: According to an AOPA note, 24% of accidents occur in the take-off or landing phase of a flight. Instructors... Let's try to get that down to 0%. j
 
"Steady State Flight"... I'm assuming you are referring to an airplane that has theoretically been trimmed into a 'hands-off' configuration requiring small flight control inputs in order to manage or control the airplane while the 'balance of forces' issue is equal to zero; i.e., unaccelerated flight.

Unaccelerated flight works too. In the flair speed and pitch are changing. There also may or may not be other things changing - transitioning from a heading to a slip to counteract crosswinds, power reductions, etc.

"Not in steady state flight" seems to me ( respectfully ) to be just another way of defining 'unstable'... Granted, all civilian airplanes are required to be stable if operated within the manufacturers limitations... I don't dispute this, but the landing flair after crossing the runway threshold, reduction of power, and increasing pitch attitude without changing the trim definitely qualifies as 'not in steady state flight'

The only reason I mentioned it was that using the term "unstable" might lead a new pilot to pay less attention to the manufacturer's limitations, especially CG limits, if they believe that an unstable airplane handles no differently than an airplane in the flare.

So, the next time you are in your landing flair, check what's happening... I think you'll find that you (the pilot) will be subconsciously watching and controlling together (1) ground closure rate and (2) longitudinal attitude of the airplane via an 'unconscious' (but properly applied) application of yoke back-pressure to set the airplane down smoothly and safely.

Well, it's been many years (decades really) since I struggled with landings as a new student pilot. As you imply, it's one of if not the hardest things for a new student pilot to learn how to perform smoothly and accurately. But every time a pilot flies a different airplane the perception issue you mentioned in the initial post has to be somewhat relearned - different airplanes present different views out the front when in the correct attitude, have different seating positions (which might affect eye position relative to the sight line over the cowl), or not even have a cowling in front of the pilot (multi-engine), different approach speeds (which affect how high the flare is started), the height of the cockpit above the runway, etc. But once the basics are learned the rest is just making slight adjustments.

Jim
 
Unaccelerated flight works too. In the flair speed and pitch are changing. There also may or may not be other things changing - transitioning from a heading to a slip to counteract crosswinds, power reductions, etc.



The only reason I mentioned it was that using the term "unstable" might lead a new pilot to pay less attention to the manufacturer's limitations, especially CG limits, if they believe that an unstable airplane handles no differently than an airplane in the flare.



Well, it's been many years (decades really) since I struggled with landings as a new student pilot. As you imply, it's one of if not the hardest things for a new student pilot to learn how to perform smoothly and accurately. But every time a pilot flies a different airplane the perception issue you mentioned in the initial post has to be somewhat relearned - different airplanes present different views out the front when in the correct attitude, have different seating positions (which might affect eye position relative to the sight line over the cowl), or not even have a cowling in front of the pilot (multi-engine), different approach speeds (which affect how high the flare is started), the height of the cockpit above the runway, etc. But once the basics are learned the rest is just making slight adjustments.

Jim

"unstable" might lead a new pilot to pay less attention to the manufacturer's limitations


Now on using the term 'unstable'. I use it for simplifying the effect the student will expect while in the flair procedure. I have never (in over 1000 students trained in landings) had this term lead to an unsafe adverse event. If anything, it enhances the students natural response to controlling the airplane in the flair configuration. This technique is primarily for the small basic trainer. When advanced TAA systems (Technically Advanced Aircraft) are introduced, the student is usually good enough at landings that this will be second nature, so to speak. My efforts are to enhance student comprehension and response to the events occuring in the flair.

Pretend for a moment that you are a new student, maybe 10 to 15 hrs flight time; and basicly understand the concept of 'stability' from initial lessons on trimming for basic maneuvers. Also assume that you have begun your landings phase of your lesson sequence. You are reasonably comfortable with the transitions from downwind configuratioin into the stabilized glide leading to base and final down to the threshold... Now you and your instructor reach the threshold and are ready to enter the flair phase of the procedure... Which of the two following cases do you think the student would respond to more effectively?

CASE I:
"Ok student, while doing this flair don't exceed the manufacturers limitations on the rotation-flair rate and maintain level flight until the energy is blead off the airplane and the wheels touch. Apply breaks gently maintaining directional control to the center line with rudders and counter applicatioin of aileron if in crosswind conditions. Hold nose up after touchdown on the mains with enough yoke back-pressure to keep the airplane from entering a nose bounce." ...OR...
CASE II:
"Level the panel dash (C172) to the horizon of the runway and maintain application of yoke back-pressure to control ground closure rate without pulling the nose through the horizon of the runway."

As the student begins to show develop a feel and perceptive understanding of the maneuver, the landing practice phrasology eventually gets simplified even more to my saying only --- OK, Remember... "Horizon of the runway and Ground Closure" ... The student instinctively applys yoke back pressure and rudder control, but more important with management of these two reference points in mind, over-control is rarely an issue. If it does occur, it's easily corrected and the airplane returned to the basic flair configuration. The student becomes very confident and quickly developes a functional feel for making safe confident landing with a very high degree of consistancy.
 
CASE II:
"Level the panel dash (C172) to the horizon of the runway and maintain application of yoke back-pressure to control ground closure rate without pulling the nose through the horizon of the runway."

This one would be easier for the student to understand and has the benefit of not bringing airplane stability into the discussion at all.

Aviation is overflowing with terms that have specific meanings. Misusing those terms does the student no favors. Over the years that aiirplanes have existed how many students have learned to land airplanes without the "benefit" of having the concept of airplane stability misused to explain what's happening in the flare? Millions?

In your "Case II" above, you didn't use the incorrect terminology and say something like "...application of rudder pressure to control ground closure rate...". Why use incorrect terminology to explain what's happening to the airplane in the flair?

Jim