Definition
An organophosphate compound added to aviation gasoline and certain lubricating oils to scavenge lead deposits and reduce spark plug fouling, valve sticking, and pre-ignition in piston engines burning leaded fuel.
Plain English
A chemical mixed into avgas or oil that helps clean up the lead leftovers from burning leaded fuel, so spark plugs and valves stay cleaner and the engine runs better.
Context Anchor
Seen in powerplant maintenance, engine oil discussions, fuel additive instructions, and product safety information.
Derivation
From 'tri-' (three), 'cresyl' (relating to cresol, a coal-tar derived compound), and 'phosphate' (a phosphorus-oxygen chemical group). The name simply describes its chemistry — three cresyl groups attached to a phosphate — but knowing it is a phosphate compound helps explain why it bonds with lead deposits and carries them out through the exhaust.
Why Pilots Care
Oils containing it improve engine durability but require careful handling because the compound is toxic if absorbed through skin.
Intuition Check
Do not assume TCP is harmless just because it is called an additive. In this context, it is a useful chemical only when used correctly, and it is toxic if mishandled.
Example Sentence 1
The owner adds TCP to each fuel tank to reduce lead fouling on the spark plugs of his Cessna 182.
Example Sentence 2
Mechanics checked the oil can label for TCP before adding lubricant to the high-time cylinder.