port side. The left side of an aircraft or ship, as viewed when looking forward.
position error (aircraft instrument error). An error in the indication of flight instruments connected to the static air system (altimeter, airspeed indicator, and vertical speed indicator). This error is caused by the air at the entrance to the static system not being absolutely still. The amount of position error changes with the angle of attack or airspeed of the aircraft and is usually greatest at low airspeeds when the angle of attack is the highest.
position line (aircraft drawings). A line used to show the extreme position to which a part can be moved.
positive charge (electrical charge). An unbalanced electrical condition caused by a deficiency of electrons. A positive charge can be produced by chemical cells, photocells, and thermocouples.
positive control. 14 CFR Part 1: “Control of all air traffic, within designated airspace, by air traffic control.”
positive control area. See PCA.
positive-displacement pump (fluid pump). A type of fluid pump that moves a specific amount of fluid each time it rotates. Since the pump is always moving fluid, some form of relief valve must be used to relieve pressure when the system cannot use the fluid as fast as the pump moves it. Gear pumps, gerotor pumps, and vane pumps are examples of positive-displacement pumps.
positive feedback (electronic amplifier). A condition in an electronic amplifier in which part of the amplified signal is fed back from the output to the input. Positive feedback, also called regenerative feedback, is used to reinforce the input signal.
positive ion. An atom that has become electrically unbalanced by losing one or more electrons. Since there are more protons in the nucleus than there are electrons surrounding the nucleus, the atom has a positive charge.
positive logic (digital electronics). The form of logic in which the more positive voltage represents a logic one and the less positive voltage or zero voltage represents a logic zero.
positive number. A number greater than zero.
positive static stability (aircraft stability). The production of a force that causes an aircraft to return to a condition of straight and level flight after it has been disturbed from this condition.
positive temperature coefficient. The change of a value, such as resistance, capacitance, or physical length, with temperature in such a way that the value increases as the temperature increases.
positive terminal (electrical power source). The terminal of a source of electrical energy through which electrons return to the source after they have passed through the external circuit.
positive vorticity (meteorology). Vorticity caused by cyclonic turning. Positive vorticity is associated with upward motion of the air.
positron. An unstable atomic particle. A positron has the same mass and spin characteristics as an electron, but it has a positive electrical charge. (An electron has a negative electrical charge.)
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