Definition
A seal installed around a moving part — such as a piston rod, shaft, or actuator — to prevent fluid (typically hydraulic fluid) from leaking past the moving surface. Packings are designed for dynamic applications, where the sealed parts move relative to each other.
Plain English
A rubber or synthetic ring that fits snugly around a moving rod or shaft to stop fluid from leaking out as the part slides or rotates.
Context Anchor
Seen in aircraft maintenance manuals, parts lists, and inspection procedures for systems that must hold pressure or prevent leaks.
Derivation
From the older mechanical practice of literally packing fibrous material (like rope or cloth soaked in grease) around a shaft to seal it. The name stuck even though modern packings are precision-molded rubber or synthetic rings.
Why Pilots Care
Worn or failed packings are a common source of hydraulic leaks. Recognizing the term helps when reading maintenance logs, discussing squawks with mechanics, or understanding why a system was deferred or repaired.
Analogy
A packing works like the rubber ring in a garden hose connection. If the ring is good and seated correctly, the connection stays dry; if it is cut or missing, it leaks.
Intuition Check
Packing does not mean luggage or cargo here. In maintenance, packing means a sealing part used to stop leakage.
Example Sentence 1
The mechanic replaced the packing on the landing gear actuator after finding hydraulic fluid weeping from the shaft.
Example Sentence 2
New packing was installed in the flap actuator gland before reassembly.