Definition
A fuel additive (tricresyl phosphate) blended into aviation gasoline to scavenge lead deposits from combustion chambers, valves, and spark plugs. TCP combines with the lead from tetraethyl lead in avgas during combustion, converting it into compounds that pass out with the exhaust rather than building up as deposits inside the engine.
Plain English
A liquid you can add to leaded aviation fuel that helps clean lead buildup out of the engine as it runs, so spark plugs and valves stay cleaner and last longer.
Context Anchor
Seen in turbine-engine operating information, maintenance manuals, and engine performance checks.
Derivation
From its chemical name, tricresyl phosphate. 'Tri' means three, 'cresyl' refers to cresol (a coal-tar derivative), and 'phosphate' is the phosphorus-oxygen group. The phosphorus is what reacts with lead during combustion to produce a compound that exits with the exhaust instead of sticking to engine parts.
Why Pilots Care
Using oil with the correct TCP level prevents premature engine wear and potential failures during flight.
Intuition Check
Tcp does not mean the computer-network term TCP here. In this aviation context, it refers to pressure inside a turbine engine.
Example Sentence 1
After switching to 100LL, the owner began adding TCP at every fuel-up to reduce lead fouling on the spark plugs.
Example Sentence 2
Mechanics check the oil can label to confirm it includes the required TCP additive before servicing.