Definition
Capable of being easily ignited and of burning rapidly. In aviation, the term is applied to fuels, solvents, and other materials that can catch fire readily at normal operating temperatures.
Plain English
Easy to set on fire and quick to burn.
Context Anchor
Seen in fuel handling, aircraft maintenance, hangar safety, fire precautions, and hazardous materials information.
Derivation
From the Latin flammare, meaning 'to set on fire.' The aviation use is the same as the everyday use — anything that catches fire easily.
Why Pilots Care
Improper handling of flammable materials or vapors can create fire risks that directly affect aircraft airworthiness and occupant safety.
Intuition Check
Do not read flammable as “safe unless already on fire.” It means the material can catch fire if the right ignition source is present.
Example Sentence 1
Avgas is highly flammable, so smoking is prohibited anywhere near the fuel pumps.
Example Sentence 2
Maintenance personnel are required to use only non-flammable solvents when working near electrical wiring.