Definition
A type of synthetic rubber (a butyl-based elastomer) known for its very low permeability to gases and its resistance to many chemicals, including phosphate-ester hydraulic fluids such as Skydrol. It is used in aircraft for seals, O-rings, hoses, tire inner tubes, and other components that must hold pressure or contain fluids without leaking.
Plain English
Butyl is a kind of artificial rubber that holds air and certain fluids really well without letting them seep through. In aircraft, it is used to make seals and similar parts that need to stay leak-tight.
Context Anchor
Seen in aircraft maintenance when choosing or identifying rubber parts, sealing tapes, sealants, gaskets, or inner tubes.
Derivation
The name comes from 'butyl,' a chemical group derived from butane. Knowing this is not essential to use the word correctly — what matters in maintenance is the material's properties, not its chemistry name.
Why Pilots Care
Using the wrong rubber compound in a seal or hose can cause rapid deterioration, leaks, or system failure. Butyl is required where the fluid or gas being contained would attack other rubbers, so matching the correct material to the application is a safety and airworthiness issue.
Intuition Check
Butyl is not a brand name or a general word for all rubber. It refers to a specific synthetic rubber material with particular sealing properties.
Example Sentence 1
The technician selected a butyl O-ring because the system used Skydrol, which would degrade a standard nitrile seal.
Example Sentence 2
Butyl liners inside the fuel cell kept the tanks from weeping even after years of service.