Graveyard Spirals

Could ignorance about airplane stability be a link in the loss-of-control accident chain?


While discussing last years Kennedy accident with a pilot friend, a significant point of disagreement was uncovered.

I outlined my conviction that some VFR-into-IMC accidents occur because many pilots dont realize that most general aviation airplanes are inherently unstable. My friend expressed doubt about my belief.

We are both retired CFIs, with a combined total of over 8,000 hours of flight instruction given, and we respect each others opinion. The heavily publicized tragedy apparently involved loss of control on a VFR night flight in marginal visibility. During televised interviews, the nefarious graveyard spiral was mentioned frequently. Many people speculated that the celebrity pilot was guilty of pilot error, recklessness, carelessness, bad judgement, inexperience and/or an inherited propensity for risk-taking.

There is another possibility that is far more ominous in that it highlights what I consider a major flaw in flight training. In virtually any mishap involving loss of control in marginal visibility or IFR conditions, ignorance could play a major role.

Some VFR-into-IMC accidents occur because many pilots dont appreciate the fact that most general aviation airplanes are inherently unstable.

Those who are surprised by that statement fall into the category of the dangerously uninformed. Most pilots have heard stories of carelessly hand-propped airplanes that take off unoccupied, fly around until the fuel runs out, and then land themselves with minimal damage. Pilots will occasionally hear (or tell) the tale of a pilot who falls asleep on a cross-country flight while not on autopilot, then wakes some time later and finds that the airplane has held heading and altitude during the course of the nap.

Those anecdotes provide graphic evidence of the inherent stability of light planes, but there is also plenty of evidence to show that they are the exception rather than the rule.

When I was working toward my CFI rating in 1949, my instructor insisted I buy a copy of Stick and Rudder, by Wolfgang Langewiesche. In this excellent book, first printed in 1944 and still available, the author devotes an entire chapter to the subject of stability, entitled What the Airplane Wants to Do. He explains, with easy-to-understand text and illustrations, why design parameters result in an airplane with a built-in tendency to enter a spiral that can rapidly develop into the well-publicized corkscrew trip to the cemetery.

Another thorough discussion of stability is found in Aerodynamics for Naval Aviators, by H.H. Hurt. After a lengthy discourse, Hurt reaches agreement with Langewiesche: Most airplanes have a built-in spiral characteristic. Although this means that a spiral could be described as a normal form of stability, its not exactly a desirable condition and would more appropriately be termed an instability.

Although the tendency to enter a spiral is described as mild, the gradual drift makes the propensity more insidious. In poor visibility, an unaware pilot may wander into a spiral without recognizing whats happening until he tries to raise the nose with the elevator. Thats the beginning of the end.

Why All the Mystery?
The FAA Flight Training Handbook, currently available as Advisory Circular 61-21A, includes a paragraph in Chapter 17 entitled Spiral Instability. Spiral aerodynamics are briefly but clearly explained. The text states that all airplanes are affected to some degree by this characteristic and improper recovery from this condition has probably been the underlying cause of more fatalities than any other single fact.

Nevertheless, most pilots are not aware that the so-called graveyard spiral is an entirely normal property of the typical general aviation airplane. As Langewiesche indicated, its what the airplane wants to do. Yet many people still have expressed wonder over how a loss of control can occur so quickly in an airplane with all equipment functioning properly.

During a career that spans 45 years as ground instructor, flight instructor, corporate pilot, designated pilot examiner and FAA Aviation Safety Inspector, I conducted many job interviews, oral exams and flight tests. I discovered that lots of otherwise competent aviators firmly believe that the Federal Aviation Regulations require general aviation airplanes to be designed with stability characteristics that result in an inherent tendency to fly straight and level.

A few poorly written textbooks, along with flight training syllabus misinformation, bolster this widespread misunderstanding. Even AC 61-21A contains a misleading and potentially dangerous statement. In Chapter 13, Emergency Flight by Reference to Instruments, it provides an unwholesome bit of teaching that contradicts the paragraph on spiral instability: The airplane is inherently stable and, except in turbulent air, will maintain approximate straight and level flight if left alone. If this statement were true, there wouldnt be any graveyard spirals.

In the not-too-distant past, a typical syllabus for both civil and military pilot training included a lesson devoted to what were described as confidence-building maneuvers. The student was invited to put the aircraft into various attitudes, release the controls and, according to one manual, observe that the airplane resumes straight and level flight. Another quote: When in doubt, release all controls and trust the airplane.

Gentle turns were defined as those that are so shallow that the inherent stability of the airplane is acting to pull up the inside wing. Fortunately, most current flight training programs do not include either the so-called confidence maneuvers or the associated untruths.

It should be noted that a few airplanes have the kind of stability most pilots believe all airplanes have. But completely stable aircraft usually have some other undesirable handling qualities. Another quote from AC 61-21A: Because it is more desirable for the airplane to have spiral instability than Dutch roll tendencies, most airplanes are designed with that characteristic.

Positive Control
Years ago, Mooney tried to defeat spiral instability by equipping its airplanes with a full-time wing leveler, more formally known as a stability augmentation device. But over the years, pilots disturbed by the necessity of cutting off the system to maneuver – and the not-so-simple task of keeping the vacuum-operated system working properly – put tape over the yoke cut-off switch to render this potentially life-saving gadget inoperative.

It should be obvious that a wing leveler would not be needed if an airplane had positive roll axis stability. Still, many pilots believe that modern general aviation airplanes should fly straight and level without pilot input.

It is unfortunate that bad texts and incomplete training have given birth to a false assumption. It has been allowed to live, possibly because of our eagerness to promote the belief among fledgling pilots and the public that airplanes are inherently safe.

When a student takes the controls on his first dual flight, he is understandably tense. So the CFI says, Relax, let go of the wheel, take your feet off the pedals, and see how nice the airplane flies. And so it does, at least for the few seconds this demonstration usually lasts. If the CFI and student would wait just a little longer (usually less than a minute) the airplane will almost always demonstrate entry into the notorious circling approach to Boot Hill.

In IMC conditions, turbulence and vertigo will probably accelerate the onset. But some pilots firmly believe an airplane that does not automatically correct a wing-low condition is suffering from poor rigging or a fuel load unbalance. Those tales of pilotless flights and cross-country snoozes – if true – prove there are airframes in existence that have positive roll axis stability. However, it must be understood that this is exceptional.

Flight Tests Silent
Unfortunately, spiral instability is not specifically mentioned in FAA Practical Test Standards for any certificate or rating. Therefore, this important bit of aeronautical knowledge is rarely included in pilot training, except perhaps by an unusually well-informed and conscientious CFI. So, the misconception lives on.

To counteract this dangerous fallacy, the reality of spiral instability should be taught to all student pilots as an important reason for not attempting to fly in poor visibility conditions without an instrument rating.

Throughout his book, Langewiesche stressed the simple and obvious idea that a pilot flies in accordance with the mental images he carries. An unknowing pilot contemplating a flight in marginal VFR conditions might delude himself into thinking that his stable aircraft will fly him straight and level to the destination, even if he cant see the horizon. The risk is multiplied if the pilot doesnt know that visibility in the vicinity of coastal airports often deteriorates in a few minutes, regardless of VFR reports and forecasts.

Installation of an autopilot may further elevate a pilots pseudo-confidence. If uninformed pilots knew that most airplanes have a built-in spiral tendency and were aware of the large number of graveyard spiral fatalities that have occurred when visibility became IMC unexpectedly, the combination of these two important pieces of knowledge might deflate their unjustified boldness and cause marginal trips to be rescheduled.

We have all heard the somewhat distressing, but partially true, statement that sagely advises that acquisition of an FAA certificate is a license to learn. However, inexperience should not be the same as incompetence. It is unfortunate that many inexperienced and incompetent pilots die as a result of something not learned – and take unsuspecting passengers with them.

Webster defines judgment as the act or process of the mind in comparing its ideas…to ascertain truth. The exercise of judgment, in any situation, is dependent on having knowledge of all critical parts of the problem.

When acting as pilot in command, this awareness must encompass a diversity of sciences and situations. If a poorly trained pilot is unaware of the problems to be faced on a planned flight, and doesnt know that he doesnt know, he cannot be accused of poor judgment.

He doesnt have enough knowledge to make a valid evaluation. Thats not poor judgment – its no judgment at all. Pilot error due to ignorance is undoubtedly an important contributory factor in many aviation fatalities.

After every well-publicized accident, the general aviation community expresses hope that no new additions will be made to the already bulging files of FARs. In some cases, this could be like saying we refuse to learn anything from experience. But most of us believe that education, rather than regulation, is the key to aviation safety. Correction of the training deficiency related to the graveyard spiral could be relatively painless, without any requirement for FAR Part 61 amendments.

Demonstrating an understanding of spiral instability should be required by the FAA Practical Test Standards for Private, Instructor and Instrument Pilot certificates. Written and oral exams should include some reference to the fact that most airplanes are designed with a tendency to enter a spiral in the absence of positive pilot control. Flight test standards should specifically require demonstration of recovery from a power-on spiral, as an addition to the present requirement for the somewhat vague recovery from unusual flight attitudes (both nose-high and nose-low).

In the aftermath of highly publicized GA accidents, general aviation seems to be critically publicized as a hobby enjoyed by inexperienced and/or untrained egoists who take needless risks. Personally, I dont think Kennedy deserved the bad press. Regardless of final NTSB determination, I believe it is unlikely that the heir to a family name that has suffered so much sadness could have been so irresponsible or complacent, or thought of himself as indestructible.

Of course, bad decisions cannot always be blamed on inadequate ground or flight training. But I am convinced that plain old ignorance is an important factor in many pilot error accidents that are too quickly attributed to poor judgment. Every time I read about a fatality that seems to involve flagrant stupidity, I wonder if the pilot didnt know that he didnt know.

And I think of an old pedagogic axiom that has always been pertinent to any education process: If the student hasnt learned, the teacher hasnt taught.

Also With This Article
Click here to view “Why Not Make It Stable?”

-by Donnal F. Smith

Donnal F. Smith is a retired CFI, CFII, ATP and designated pilot examiner.


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