Definition
A chemical substance added to aviation fuel or fuel-system components to kill or inhibit the growth of microorganisms — bacteria, fungi, and yeasts — that can live in the water-fuel interface of fuel tanks and cause corrosion, filter blockage, and fuel system contamination.
Plain English
A chemical added to fuel or fuel tanks to kill the tiny living organisms that can grow inside them. These organisms feed on fuel and water, and if left alone they corrode tanks and clog fuel filters.
Context Anchor
Seen in fuel system maintenance, especially when checking for fuel contamination, sludge, or growth inside tanks and filters.
Derivation
From Latin 'bio' meaning life, and 'cide' meaning to kill. So 'biocidal' literally means life-killing — in this case, killing the microbes living in the fuel.
Why Pilots Care
Uncontrolled microbial growth can clog filters, corrode tanks, and cause loss of engine power.
Intuition Check
Do not read “agent” as a person or representative here. In this term, an agent is a substance that produces an effect: killing unwanted biological growth.
Example Sentence 1
After finding signs of microbial growth during the fuel tank inspection, the technician treated the tank with an approved biocidal agent.
Example Sentence 2
Fuel samples are tested to confirm the biocidal agent is still effective against contamination.