Definition
A form of corrosion in aircraft fuel tanks caused by living microorganisms — bacteria, fungi, and yeasts — that grow at the interface between water and jet fuel. These organisms feed on hydrocarbons in the fuel and produce acidic waste products that attack metal tank surfaces, particularly aluminum, leading to pitting and structural damage.
Plain English
Tiny living organisms grow where water collects in a fuel tank and slowly eat away at the metal, causing damage over time.
Context Anchor
Seen in aircraft maintenance discussions, especially around fuel tanks, sumps, drain areas, bilges, and any place where water can collect and sit against metal.
Derivation
From 'micro' (Greek mikros, small) and 'biological' (relating to living organisms). The term simply names what causes the corrosion: very small living things, rather than a chemical or electrical process.
Why Pilots Care
Left unchecked it can create leaks, weaken tank structures, and contaminate fuel, leading to engine problems or expensive repairs.
Grounding Statement
If water sits in a hidden aircraft area long enough, tiny organisms can grow there and create chemicals that attack the metal.
Intuition Check
Microbiological corrosion does not mean the airplane is “infected” like a person. It means tiny organisms in damp areas can create conditions that make metal corrode faster.
Example Sentence 1
The mechanic found signs of microbiological corrosion in the fuel tank after the aircraft had sat unused for several months with water in the sumps.
Example Sentence 2
Microbiological corrosion in the wing tanks required treatment with a biocide additive after the discovery of sludge.