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FACE VALIDITY. Apparent relevance or appropriateness of a measure.
FAIL SAFE. Characteristic of system that avoids injury to humans and/or catastrophic damage when an element malfunctions.
FATIGUE. Decreased ability to perform and/or feelings of tiredness following effort.
FAULT. Abnormal condition in a controlled system, possibly leading to system failure.
FAULT LOCALIZATION. Systematic procedure for identifying malfunctioning element of a system.
FAULT TREE ANALYSIS. A logical approach to identify the probabilities and frequencies of events in a system that are most critical to uninterrupted and safe operation. This analysis may include failure mode and effect analysis (determining result of component failure interactions towards system safety) and Techniques for Human Error Prediction (THERP).
FEEDBACK. Data on the performance of a system, equipment, group, or individual for use in modifying performance.
FIDELITY. (1) The degree to which a system’s output duplicates the input. (2) The faithfulness with which a simulation represents features of a system.
FIELD OF VIEW. The solid angle within which an optical sensor (such as the human eye) provides useful data.
FIELD STUDY. Form of scientific investigation in which activities in actual work environments are observed.
FLASH BLINDNESS. Temporary loss of vision for low-luminance objects following brief exposures to intense light.
FLICKER. Rapid yet perceptible changes in display luminance.
FLICKER FUSION. The tendency of an oscillating or flickering sensory input signal to be observed as continuous. At a certain threshold frequency (typically above 6 Hz for vision), the perceiving apparatus, (e.g., eye, ear, tactile or other sensory areas) is no longer able to separate the individual pulses and instead perceives one continuous signal. This effect makes motion pictures seem to run smoothly. Flicker fusion caused, for instance, by low frequency fans or objects on fast conveyor belts passing before a light source, may lead to errors such as seeing a moving saw blade apparently at rest, and leading to accidents (See STROBOSCOPE.)
FLIGHT DECK. Workstation in an aircraft cockpit.
FLIGHT SIMULATOR. A ground-based device containing a representation of an aircraft cockpit with a computer driving functional displays and controls. It may be used for training, for research, or for engineering development.
FLIGHT TRAINER. A ground-based device containing a representation of an aircraft cockpit, used for pilot training. It need not have the fidelity of a flight simulator.
FLYBAR (FLYING BY AUDITORY REFERENCE). A system providing turn, bank, and air speed information via auditory signal, rather than with conventional flight instruments.
FOOT CANDLE. An obsolete measure of the intensity of illumination of a surface, or, the flux density of light incident on a surface. A flux of 1 lumen per square foot of surface is defined as 1 foot candle of illumination. It is no measure of the light reflected from a surface and, therefore, no “index of visibility” of an object to the worker. (See BRIGHTNESS CONTRAST, VISUAL ACUITY, REFLECTANCE, FOOT-LAMBERT.)
FOOT-LAMBERT. An obsolete measure of the illumination flux density reflected from a surface. Used in measurement of the effectiveness of workplace lighting, the foot-lambert is the only accurate index of light actually perceived by the eye: equals 1/π candles per square foot. (See REFLECTANCE.)
FORCE JOYSTICK. Control in which input corresponds to applied force.
FORCE-PACED. Experimental or actual task in which a performer's activity is paced by external events.
FORWARD CHAINING. An automated or human reasoning strategy in which a sequence of actions are sought to transform a problem from an initial or given state to a goal state.
FUNCTION ALLOCATION. Stage of system design in which specific functions are assigned to individuals or automated systems.
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