pitch pocket (wood defect). Cavities filled with pitch that appear in the growth rings of a piece of wood.
pitot pressure. Ram air pressure used to measure airspeed. The pitot tube faces directly into the air flowing around the aircraft. It stops the air and allows the pressure caused by its movement to be measured.
pitch setting. 14 CFR Part 1: “The propeller blade setting as determined by the blade angle measured in a manner, and at a radius, specified by the instruction manual for the propeller.”
pitot-static tube. A combination pickup used to sample pitot pressure (ram air pressure) and static pressure (still air pressure). These two pressures, taken from outside a moving aircraft, are combined to measure airspeed. Pitot pressure is picked up through an open-end tube that sticks directly into the airstream, and static pressure is picked up through small holes or slots in the side of the pitot-static tube, or through flush ports on the side of the aircraft.
pitot tube. An open-end tube that points directly into the air flowing over an aircraft structure. The pitot tube samples the pressure of the ram air. This pressure is taken into the airspeed indicator where it is compared with static air pressure to produce the airspeed indication.
pitting corrosion. A type of corrosion that forms on the surface of metal as small, localized pits filled with the salts of corrosion.
PK screw. See Parker-Kalon screw.
placard. A notice placed on an aircraft in plain sight of the appropriate crew member to give information pertinent to the operation of the aircraft. Operations limitations as well as maintenance specifics are often displayed by placards.
plain bearing. A bearing made of a material, such as lead or babbitt, that has a low coefficient of friction. Plain bearings can support only loads applied in a direction perpendicular to their surface, and are used as crankshaft bearings in most reciprocating engines.
plain flap (aircraft secondary control). A type of wing flap in which a part of the wing trailing edge inboard of the aileron is hinged to fold downward in flight to change the camber of the wing.

plain nut. A form of hexagonal nut that has no provisions for locking it onto a bolt or stud.
plain overlap seam (aircraft fabric seam). A type of machine-sewed seam used to join two pieces of aircraft fabric. The edge of one piece of fabric overlaps the edge of the other, and one or two rows of stitches are used to join the pieces. In a plain overlap seam, the thread passes through two layers of fabric.

plain rib (airplane wing rib). A wing rib used to give the wing its airfoil shape. Plain ribs are also called former ribs.
plain washer (aircraft hardware). A disk of metal with a hole in its center. Plain washers are used to provide a smooth surface on which a nut can ride, and to fill the space between a surface and the nut to adjust for the grip length of a bolt.