Turbine powered aircraft accidents due to loss of control, caused by an upset during flight, are a leading cause of aircraft accident fatalities in the world. An aircraft upset can be caused by, for example, a pilot's deviation from controlled flight or external elements (e.g., wind shear or wake turbulence). A major cause of aircraft upsets and subsequent loss of control in turbine powered aircrafts is an aerodynamic stall.
An aerodynamic stall occurs when the wing's critical angle of attack is exceeded. The airspeed at which an aircraft exceeds the critical angle of attack varies based on, for example, aircraft weight, load factor, and slideslip (uncoordinated flight). With respect to a given aircraft, the critical angle of attack (CoA) is the same for a given configuration. For example, leading edge slats and trailing edge flaps can change the critical angle of attack by altering the overall shape of the airfoil. Regardless of the configuration, when the CoA is exceeded, airflow disruption over the upper surface of the wing occurs, which creates a loss of lift that can result in an insufficient amount of lift to maintain flight. The CoA is a function of pitch attitude, which, in some aircrafts, the pilot can control via an elevator attached to a horizontal stabilizer. In other aircrafts, the pilot can control the pitch attitude via a combination of horizontal stabilizer and elevator movement. Using the control column, which generally includes a yoke, flight controls, and a control wheel, a pilot can control a given aircraft's pitch attitude and angle of incidence by fore and aft movements. During normal flight operations, an increase in pitch attitude requires an increase in aircraft power to retain an airspeed above that which the CoA requires. A decrease in pitch attitude, while the aircraft power remains constant, results in the acceleration of the aircraft, and thus an increase in airspeed.
When the angle of incidence (AI) of an aircraft approaches the CoA of the aircraft, the aircraft may be approaching a stall. Certain factors and conditions are often present when an aircraft approaches a stall. For example, there may be an increase in pitch attitude or an increase in control column back pressure. A stall may also be preceded by decreasing airspeed and diminished flight control effectiveness. In some cases, a turbo jet powered aircraft that has a high speed airfoil and negative pitch angle can approach a stall. An aircraft spin can occur as a result of a stall. For example, when the aircraft wing of a turbine powered multi-engine aircraft exceeds the critical angle of attack (CoA), often one wing will stop flying ahead of the other as a result of engine power and aerodynamics. Thus, when one wing stalls ahead of the other, the stalled wing can drop as the nose of the aircraft violently pitches forward or aft. Such spins can be deadly, for example, at low altitudes or when performed by turbo jet aircrafts.
To recover a given aircraft from an impending stall, typically a pilot must simultaneously decrease the pitch attitude and increase aircraft thrust. Additionally, if the aircraft is in a turn for example, the pilot should roll the aircraft so that the wings are in a level state. Thus, to recover from an impending stall, generally forward pressure is applied to the control column to reduce the pitch attitude, and thus the AI, to a margin safely below the CoA. Pilots are typically trained to recognize stalls and to recover from stalls, for instance every 6 or 12 months. Furthermore, turbine powered aircraft are generally equipped with stall warning systems and stall protection devices (e.g., stick pushers).
Despite pilot training and current safety systems, aircraft accidents continue to occur. It is recognized herein that existing approaches to preventing aircraft accidents lack capabilities.
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