Definition
A pitch pocket is a defect in wood consisting of a well-defined opening or cavity between the annual growth rings of a tree, containing or having contained solid or liquid pitch (resin). When found in wood intended for aircraft structural use, it is treated as a defect that may weaken the material or compromise glue bonds.
Plain English
A small pocket or gap inside a piece of wood, sitting between the growth rings, that holds (or once held) sticky tree resin. In aircraft wood, it counts as a flaw because it can weaken the wood or stop glue from sticking properly.
Context Anchor
Seen during inspection or selection of wood used in aircraft structures, such as wooden spars, ribs, or other load-carrying parts.
Derivation
Pitch here refers to the thick, sticky resin that flows from coniferous trees, from the Latin pix meaning tar or resin. Pocket carries its everyday sense of a small enclosed cavity. Together: a small enclosed cavity in the wood holding tree resin.
Why Pilots Care
An undetected pitch pocket can weaken the wood and lead to structural failure under flight loads.
Intuition Check
Pitch does not mean the airplane’s nose-up or nose-down angle here. In this term, pitch means sticky resin from a tree.
Example Sentence 1
During inspection of the spruce stock, the technician rejected a board that contained a pitch pocket near the area intended for a glue joint.
Example Sentence 2
Pitch pockets in a wooden propeller blade must be cut out and repaired before the prop is returned to service.