August 1, 1989
Mark R. Twombly
The word "spin" often is infused with dark implications. "His head is in a spin" we say of someone whose mental faculties have derailed. A "spin doctor' attempts to disguise unpleasant truths in euphemistic platitudes. And then there is the stall/spin, as in an airplane rapidly corkscrewing its way toward terra firma. Dark implications indeed.
Spins top the list of dreaded maneuvers among pilots who have never experienced one. There is plenty of reason for dread if the spin comes as a surprise low to the ground. But done properly, which means an intentional spin performed at a safe altitude by a qualified pilot in a properly certified and equipped airplane, spins can be a positive challenge to add to a pilot's resume of experience and skills.
One of the greatest benefits of spin training is disciplining the mind to stay in focus as events unfold. When a spin begins to develop, time appears to accelerate. The nose drops through the horizon to what appears to be a near-vertical attitude, and the airplane begins to rotate at an increasingly fast rate. The mind can quickly become panicked, confused, or paralyzed, and the chances of initiating a recovery can diminish. If you understand what is taking place in a spin and are able to think your way through it, you are much more likely to respond to an unusual situation quickly and correctly.
The catalysts for a spin are a stall and a yawing moment. Remove either, and the spin falls apart. Maintain them, and the spin progresses from the incipient phase, in which the pitch attitude and rate of rotation are changing, to the steady state characterized by relatively constant airspeed, rotation, and pitch attitude. At this point aerodynamic and inertial forces are in balance, and the airplane is autorotating, scribing a helical path around a vertical axis. To recover, pull the power back to idle, apply full opposite rudder to stop the autorotation, and move the stick forward to break the stall. Center the rudder and apply aft stick to return to level flight without exceeding airspeed and load limitations. Recovery procedures differ in some airplanes. The pilot's operating handbook is the final authority.
An intentional spin usually is initiated by applying full rudder at the moment of stall in the direction you want to spin. An unintentional spin can follow a stall if the pilot unknowing holds rudder or cranks the stick or yoke over in an attempt to pick up a dropping wing. Adverse yaw from the downwardly deflected aileron causes increased drag, which forces the wing lower. The low wing has a higher angle of attack in relation to the relative wind and is stalled, so it continues to drop. The high wing has a lower angle of attack and is generating some lift, so it continues to rise. The spin progresses, feeding upon itself.
Spins come in several flavors: over the top, out the bottom, flat, and inverted. Let the airspeed decay and angle of attack increase in a steep, climbing right turn with too little right rudder, and a stall could occur, followed by a roll to the left and an over-the-top spin to the left. A stall in a steep base-to-final left turn with excess bottom rudder can lead to an out-the-bottom spin to the left. A flat spin involves only yaw — no pitch or roll — and can result from a stall with aft center of gravity. Aerobatic pilots perform inverted spins by stalling while the airplane is upside down. Recovery calls for aft stick to break the stall. An upright spin can turn into an inverted spin if, during recovery, too much forward stick is applied before rotation stops.
Since a stall can occur at any airspeed and attitude, it follows that a spin can, too. A snap roll is a high-speed spin resulting from an accelerated stall.
Before mid-1949, student and aspiring commercial pilots had to undergo spin training and demonstrate spins during flight tests. Despite the training, 48 percent of fatal accidents from 1945 to 1948 involved stalls followed by spins. The Civil Aeronautics Board responded by shifting the emphasis in training from spins to recognizing the onset of a stall and recovering before the stall could degenerate into a spin. Private and commercial pilot applicants no longer were required to demonstrate a spin during their flight tests. The change also led to the development of more spin-resistant airplanes.
Stall and spin resistance is built into an airframe by limiting elevator travel to prevent deep stalls and using differential aileron deflection to reduce adverse yaw. Stall strips are attached to wing leading edges to maintain airflow over the airfoil at high angles of attack, and the outboard portion of the wing is twisted to a lower angle of incidence so the tips continue to generate lift when the wing root is stalled. Cessna added a slight leading edge droop to the wings of some 172 models to improve high angle of attack flight characteristics.
Extensive stall/spin testing by the National Aeronautics and Space Administration has led to the development of a more pronounced leading edge cuff on the outboard portion of the wing. The cuff effectively lowers angle of attack so that a stall in the inboard section of the wing will not spread to the tips and ailerons. The pilot can maintain lateral control with ailerons. NASA's cuff concept is used on kit aircraft such as the Questair Venture but has not appeared on a certified production model yet.
Today, the only spin training required of pilots is for a certified flight instructor (single-engine airplane and glider) rating. The candidate must demonstrate competence in entry, spin, and recovery from a one-turn spin to the left and to the right. A flight-test examiner can, however, elect to forgo having the applicant actually demonstrate spins and instead ask to see a logbook endorsement from the applicant's instructor attesting to spin competency.
Some 30 years after spin training was dropped for all but CFI applicants, the incidence of fatal stall/spin accidents, as a percentage of all accidents, had declined 75 percent. The National Transportation Safety Board, in a 1972 report analyzing stall/spin accidents, said that an emphasis in training on recognizing and recovering from stalls was the key factor.
NTSB's finding raises an interesting question. If more rigorous stall avoidance training is the key to reducing stall/spin accidents, would not spin training be an enhancement? Should spin training once again be required of all pilots? The debate has raged for four decades and continues today. Six years after mandatory spin training was dropped, NTSB recommended that spin recovery training be made a prerequisite for soloing. The FAA, citing public opinion favoring stall recognition, said no.
NTSB tried again. In 1972 the safety board asked the FAA to study the feasibility of requiring at least minimal spin training of all pilot applicants. Again the FAA declined. Most stalls/spins that end in accidents occur on takeoff, approach, or as a consequence of buzzing or aerobatics — too low to the ground to recover. Since there can be no spin without a stall, the FAA reasoned, the training emphasis must be on recognizing and avoiding the onset of a stall.
The issue is back on the front burner. The FAA is rewriting regulations governing the training and recurrency of pilots. One area under scrutiny is stalls and spins. The FAA is proposing to strengthen the training in stall recognition and recovery by introducing the element of distractions during slow flight.
The thinking is that since most stall/ spin accidents occur as a result of the pilot's attention being drawn from monitoring attitude and airspeed, an effective stall/spin training scenario would be for an instructor to distract a student while practicing slow flight. Ground school instruction would be expanded to include more stall/spin awareness and recovery techniques. Flight instructor candidates would be required to demonstrate spin competency as part of their instruction. The FAA does not, however, endorse mandatory spin and spin recovery flight training for private and commercia1 pilot applicants.
Even if spin training were reinstated, daunting logistical problems must be faced. Urban flight schools in particular would find it difficult to identify suitable spin practice areas away from controlled and congested airspace. The pool of training airplanes certified for spins, primarily the Cessna 150/152 and Piper Tomahawk, is aging and shrinking. Flight schools would face higher insurance premiums and maintenance costs. Potential students who fear spins may be driven away. Most important, few flight instructors are proficient in spin training. It would take a great deal of time and money to bring the flight training fleet, curriculum, and instructors up to spin training standards.
Spin training may not be required, but there is nothing to stop a student or licensed pilot from seeking it. An aerobatic school is a good place to begin the search. Spin training is an aerobatic school's bread and butter. Instructors are experienced in demonstrating spins and other unusual-attitude maneuvers, and the airplanes are certified for higher G loads. Aerobatic airplanes also have quick-release canopies or doors and, more than likely, fuel and oil systems capable of functioning in inverted flight.
The FAA defines an aerobatic maneuver as one involving an abrupt change in attitude or an abnormal attitude or acceleration other than what might be encountered in normal flight. Without question, a spin is an aerobatic maneuver. As such, spins must be performed away from congested areas or crowds, outside of control zones and federal airways, above 1,500 feet agl, and in at least three miles flight visibility. Parachutes must be worn, unless it's a training flight for a CFI rating check ride.
All single-engine airplanes certified under Federal Aviation Regulation Part 23 have at least some spin recovery potential, although not all are approved for spins. Normal category airplanes must be able to recover from a one-turn or three-second spin, whichever takes longer, in not more than one additional turn. The one-turn spin test is considered an investigation of controllability in a delayed recovery from a stall, rather than a true spin recovery test. Normal category airplanes are not approved for spins, and to attempt them is to explore uncharted territory.
Airplanes certified in the Acrobatic category must demonstrate recovery from the longer of a six-turn or three-second spin in no more than one and a half turns. If the airplane has flaps, it must recover from a one-turn or three-second flaps-extended spin. Utility category airplanes approved for spins must meet acrobatic recovery standards.
Multiengine airplanes do not have to meet spin recovery standards. It may appear to be asking the impossible to recover from a spin in a twin with one engine shut down, but with some it can be done. Beech Aircraft conducted a complete series of spin tests on the Duchess while it was undergoing certification flights. Company test pilots performed multiple-turn, engine-out spins and found that recovery is possible.
Rudder effectiveness has much to do with spin recovery potential. If the rudder is blanked out in the spin by the horizontal stabilizer and elevator, yaw control is lost. Applying full opposite rudder may not stop the rotation.
Some airplanes are designed to be difficult to spin. It takes a lot of effort to coax a Cessna 172 into a spin. Elevator and rudder travel are limited, which restricts angle of attack and yaw. The POH recommends quick deceleration just before the stall to achieve a sharper stall break, deflecting the ailerons into the spin — left spin, left aileron — and a momentary shot of power at the entry. Even then, the spin will be sluggish at best and degenerate into a spiral.
A spiral differs from a spin in that the airplane is not stalled. Airspeed and G loads increase quickly in a spiral, and delaying power reduction and recovery could overstress the airframe.
Randy Gagne, an aerobatic instructor at Pompano Air Center in Pompano Beach, Florida, and I donned parachutes one afternoon and went spinning in one of Pompano's 172s. True to form, the airplane was very reluctant to cooperate. The best we could manage was a one-turn spin before the airplane started flying again in a spiral.
We also tested the hands-off recovery method: Reduce power to idle and let go of the controls. The Cessna recovered on its own. Eric Mueller, a Swiss aerobatic pilot, is credited with developing the technique, while Gene Beggs, an aerobatic performer and instructor, has introduced it to the United States. Many aerobatic schools now include this technique in their spin training curriculum. The technique is said to work in many, but not all, airplanes.
One benefit of spin training that should not be discounted is pleasure. Once the initial jitters subside, spins can be lots of fun to practice and perform with skill. Aerobatic pilots practice precision spins by stopping the rotation at a precise point — for example, one and a half turns. It takes a fine sense to know just when to feed in enough opposite rudder to stop the yaw, relax just enough back pressure to break the stall, and neutralize the controls at the right moment so the airplane pops out of the spin in a perfect vertical dive, the heading spot on.
Facing up to spins may be the only way to overcome a fear of them. Spin training can boost confidence in the ability to cope with any unusual attitude or loss of control. It also gives the pilot a better idea of the relationship and proper coordination of flight controls, especially the rudder.
The training probably won't be of much help if a spin occurs at low altitude. But it is reasonable to expect that a pilot familiar with spin entry and recovery techniques should be able to recognize when a low, tight turn from base to final begins to go sour and, rather than panicking, react intelligently.
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