Definition
A type of synthetic resin that cures, or hardens, only in the absence of air. It remains liquid while exposed to oxygen and sets into a solid bond once it is sealed between two close-fitting metal surfaces, such as threaded fasteners or shaft fittings.
Plain English
A liquid adhesive or sealant that stays soft while it is open to the air and only hardens once it is trapped between two metal parts where no air can reach it.
Context Anchor
Seen in aircraft maintenance instructions for securing threaded hardware, sealing fittings, or retaining closely fitted parts.
Derivation
From Greek 'an-' (without) and 'aer' (air), plus the everyday meaning of resin as a sticky, hardening substance. Together it literally means 'a hardening substance that works without air' — which is exactly how it behaves.
Why Pilots Care
Pilots and mechanics encounter anaerobic resins as thread-locking and sealing compounds (such as Loctite products) used on bolts, fittings, and accessory cases. Using the correct type ensures fasteners stay secure under vibration and that joints remain leak-free.
Intuition Check
Do not think of anaerobic resin as something that simply dries in open air. It usually stays liquid in the bottle and hardens only when air is excluded between fitted parts.
Example Sentence 1
The mechanic applied a drop of anaerobic resin to the bolt threads before torquing the fitting to prevent it from backing off in service.
Example Sentence 2
During the annual inspection, the technician checked for signs of anaerobic resin on the landing-gear attach bolts to confirm they had been properly secured.