Accidental spins are still today among the list of the most deadly GA aviation accidents. Years ago, private pilot applicants were required to demonstrate spins, so spin training was a routine part of the private pilot curriculum, later the FAA removed the requirement for spin training for private pilots, substituting increased training in stall recognition and recovery, since spins cannot occur without a stall. (A requirement for instructional proficiency in spins remains today only for flight instructor candidates).
A spin in a small airplane is a controlled or uncontrolled maneuver in which the airplane descends in a helical path while flying in a stalled condition at an angle of attack greater than the angle of maximum lift. Spins result from aggravated stalls in uncoordinated flight. In an aggravated stall, one wing will drop before the other and the nose will yaw in the direction of the low wing.
Two elements must be present in order for an airplane to spin: stall & yaw. By themselves, neither stalling nor yawing result in spinning; however, simultaneously stalling with sufficient yawing always results in a spin.
The spin is a high Drag maneuver. Consequently, airspeed will not continue to increase, but will generally stabilize at a relatively low and constant value. And once the spin develops (usually two to four turns), rate of rotation will stabilize as well.
Types Of Spins
- An incipient spin is that portion of a spin from the time the airplane stalls and rotation starts, until the spin becomes fully developed. An incipient spin that is not allowed to develop into a fully developed spin is commonly used as an introduction to spin training and spin recovery techniques.
- A fully developed spin occurs when the aircraft angular rotation rates, airspeed, and vertical speed are stabilized from turn-to-turn in a flight path that is close to vertical.
- A flat spin is characterized by a near level pitch and roll attitude with the spin axis near the C of G of the airplane. Recovery from a flat spin may be extremely difficult and, in some cases, impossible.
The primary cause of an inadvertent spin is one wing exceeding the critical angle of attack while executing a turn with excessive or insufficient rudder, and, to a lesser extent, aileron.
In an uncoordinated maneuver, the pitot/static instruments, especially the altimeter and airspeed indicator, are unreliable due to the uneven distribution of air pressure over the fuselage. The pilot may not be aware that the critical angle of attack is about to be exceeded until the stall warning device activates. If a stall recovery is not promptly initiated, the airplane is more likely to enter an inadvertent spin. The spin that occurs from cross-controlling an aircraft in a skidding turn usually results in rotation in the direction of the rudder being applied, regardless of which wing tip is raised.
In a slipping turn, where opposite aileron is held against the rudder, the resultant spin will usually occur in the direction of the applied rudder and opposite the aileron that is being applied.
Spinning ceases if and when forces and moments opposing autorotation overcome pro-spin aerodynamics. Since yaw coupled with roll powers the spin, we must forcibly uncouple them to effect recovery. Full opposite rudder is the primary means through which this is accomplished.
During the recovery phase, the nose attitude steepens. The rate of rotation ultimately decreases, too. Recovery can occur in as little as a quarter of a turn, or can take several additional turns depending on the airplane and the dynamics of the spin.
Inherent design differences between airplanes influence the effectiveness of spin recovery actions. Flight within the acrobatic category, for example, demands greater control effectiveness than operation in the normal or utility categories. Acrobatic category designs also must comply with more stringent spin test requirements. (See “A New Pilot’s Guide to Aircraft Categories,” August 1993.) As a result, aerobatic airplanes tend to display good-to-excellent recovery characteristics by design.
Since recovery capability from developed spins is not a design criterion for normal category aircraft, it’s reasonable to assume that such airplanes might display poor recovery characteristics by design. This assumption was validated repeatedly during the NASA spin test program (1977-87), where unrecoverable spins often were encountered beyond the one-turn margin of safety.
Recovery inputs must be applied in the proper sequence whenever an inadvertent spin is entered. Knowing what to move, where to move it, and when to move it are the keys to successful spin recovery. Since an inappropriate input could negate other recovery actions, let’s briefly describe how our control inputs influence spin characteristics.
The application of power usually drives the airplane deeper into the spin and can delay recovery. Gyroscopic effects associated with a rapidly rotating propeller can lead to increased rates of rotation and shallower spin attitudes – flat spins. In fact, flat spins, which are resistant to recovery procedures depending on the airplane, can be excited simply by applying full power. Therefore, the throttle should be retarded to idle as soon as possible to avoid aggravating the spin.
Deflecting the ailerons in the direction of rotation tends to steepen the spin attitude, reduce the yaw rate, and increase the magnitude of any roll or pitch oscillations. Deflecting the ailerons in the opposite direction tends to flatten the spin attitude, increase the yaw rate, and dampen any roll or pitch oscillations. The combination of full power and opposite ailerons can drive an airplane into a fully developed flat spin. Neutralizing the ailerons by moving the stick or yoke to the “wings level” position, therefore, is the best course of action during an inadvertent spin.
Applying full rudder opposite to the direction of rotation is always recommended for spin recovery. This is the primary action that needs to be performed. If unsure of which way the airplane is spinning, look at the airplane symbol on the turn coordinator and step toward the “high” wing (the attitude indicator, heading indicator, and the slip/skid ball are unreliable in a spin); or look straight down the nose of the airplane and step in the direction in which the ground appears to be “flowing” past the nose; or feel for a rudder pedal that offers more resistance and step on the “heavy” one.
Full opposite rudder alone may not always be sufficient for recovery from developed spins. It often must be used in conjunction with other spin recovery actions. Even so, once the direction of the spin has been determined, briskly push opposite rudder all the way to the control stop.
Moving the elevator around in developed spins can aggravate spin characteristics and may delay recovery. Common to all airplanes, pushing the elevator forward during an upright spin accelerates the rotation. This phenomenon may even be observed briefly during the normal recovery process. In some configurations, premature elevator inputs can induce a non-recoverable flat spin!
Applying the opposite rudder first, then pushing the elevator forward is a critical sequence of events for recovery from developed, upright spins. “Pushing forward” means different inputs for different airplanes. Don’t experiment on your own fly with a qualified flight instructor. The final position of the elevator control during spin recovery depends on the airplane and the dynamics of the given spin. In developed upright spins in non-aerobatic airplanes, anticipate the need for brisk elevator movement forward of neutral, possibly fully forward, following the rudder input. With the enhanced control authority typical of aerobatic airplanes, anticipate having to move the elevator control briskly to neutral, or slightly beyond. In either case, the elevator control should be driven forward after the application of full opposite rudder.
Procedure vs. technique
Spin recovery actions do not follow a pilot’s natural instincts, nor the reactions reinforced during normal training. Spin recovery actions are a learned response. They are purely a mechanical process devoid of the usual sense of control feel developed in normal flight.
Efficient spin recovery is predicated on the occurrence of specific actions, namely: Power — Off, Ailerons — Neutral, Rudder — Full Opposite, and Elevator —Briskly Through Neutral. These actions form the essence of spin recovery procedure. They outline “what” needs to happen. “How” these actions are implemented defines spin recovery technique. Maximizing the probability of recovery hinges on applying appropriate techniques to satisfy the intent of the procedure.
For example, there are at least three techniques that will satisfy the Power-Off requirement: retard the throttle, pull the mixture to idle cut-off, or run out of fuel. In most cases, retarding the throttle is the most efficient way to get the power off. Option two would come in handy if the throttle linkage was broken. Option three … it’s not really a viable or desirable option, is it?
Whether spin recovery technique describes a simultaneous application of recovery controls, a step-by-step application, a timed delay between the opposite rudder and forward elevator inputs, a prescribed amount of forward elevator, or a hands-off-the-stick approach, the procedural elements outlined above must be addressed.
Looking to simplify the learning process, the PARETM (pronounced “pair”) acronym evolved in the late 1980s as a convenient way of presenting spin recovery information to pilots engaged in spin training. It offers the same recovery actions recommended by NACA, NASA, the FAA, and many spin experts and airplane manufacturers, but in a more concise format.
Consolidating, simplifying, and prioritizing the rudimentary spin recovery actions yields the PARE procedure:
P=Power — Off.
A=Ailerons — Neutral (& flaps up).
R=Rudder — Full Opposite.
E=Elevator — Briskly Through Neutral.
Hold these inputs until rotation stops, then:
Rudder — Neutral.
Elevator — Recover to Straight and Level.
The letters in the PARE acronym spell out the sequence of events. Each item in the checklist is performed one step at a time. As soon as one item is completed, the next one is initiated until all four primary controls have been positioned for spin recovery.
The important rudder-then-elevator sequence appears twice: first to stop the spin, then while returning the airplane to level flight.
Remember, reversing the order of these inputs during a spin can aggravate the situation. Reversing them after the rotation has stopped could lead to a secondary spin in the opposite direction! While classroom discussions about stalls and spins are educational, there is no substitute for hands-on experience in a controlled, dual-instruction environment. The value of spin training lies in its ability to stretch your operating envelope. It strives to improve your coordination and awareness skills.
The typical stall / spin accident it is largely a pilot driven process that culminates in a stall or spin prior to ground impact. Stall / spin accidents evolve as a chain of events with warning signs that, if recognized and corrected, can be broken before reaching the spin. Proficiency in the elements of a comprehensive, scenario based stall / spin training program should provide pilots with the awareness and skills to prevent an accidental spin departure in the first place.
If this article has inspired you to take some spin training, find a qualified instructor who has access to an approved, well maintained spin trainer. Most of the ingredients necessary for safe, quality spin instruction usually can be found at schools specializing in emergency maneuver and aerobatic training.
Source/s: East Hill Flying Club; FAA Stall / Spin Recovery Training; Spin Training Transport of Canada; Rich Stowell Stall / Spin Myths Exposed