Definition
Tricresyl phosphate (TCP) is a chemical fuel additive used in aviation gasoline to help control lead deposits left behind when leaded fuel (such as 100LL) burns inside a piston engine. It reacts with combustion byproducts to form compounds that pass out through the exhaust instead of building up on spark plugs, valves, and combustion chamber surfaces.
Plain English
TCP is a substance added to leaded aviation fuel that helps clear out the lead deposits the fuel would otherwise leave inside the engine.
Context Anchor
Seen in aircraft maintenance discussions of engine oil, hydraulic fluid, leaks, fumes, and handling precautions.
Derivation
The name describes the chemistry: tri- means three, cresyl refers to cresol (a compound related to phenol), and phosphate means it contains a phosphorus-oxygen group. Knowing it is a phosphorus compound helps explain why it works — the phosphorus reacts with lead during combustion to form a compound that exits with the exhaust rather than sticking to engine parts.
Why Pilots Care
Lead fouling on spark plugs is a common cause of rough running and failed magneto checks in piston aircraft burning 100LL. TCP is one of the tools mechanics and operators use to reduce that fouling, so pilots may encounter it referenced in maintenance records, service bulletins, or fuel additive discussions.
Grounding Statement
TCP is useful inside certain aircraft fluids, but it is not something people should breathe, swallow, or handle casually.
Intuition Check
Do not read TCP here as a computer or radio term. In this maintenance context, TCP means a toxic chemical found in some aircraft fluids.
Example Sentence 1
The mechanic recommended adding TCP to the fuel to reduce the spark plug fouling the owner had been seeing during runup.
Example Sentence 2
Technicians wore gloves when handling drained oil because TCP can irritate skin.