Definition
A chemical compound that releases hydrogen ions when dissolved in water, has a pH below 7, tastes sour, and reacts with metals and bases. In aviation, acids appear most commonly as the sulfuric acid electrolyte in lead-acid batteries and as cleaning, etching, or testing agents used in maintenance.
Plain English
A chemical that is corrosive, can eat away at metal, and is the active liquid inside a standard aircraft battery. The opposite of a base or alkaline substance.
Context Anchor
Seen in aircraft battery servicing, battery safety instructions, corrosion discussions, and maintenance manuals.
Derivation
From the Latin acidus, meaning sour. The original sense referred to taste — acids taste sour, like vinegar or lemon juice — and the chemical meaning grew from there.
Why Pilots Care
Battery acid can spill, leak, or vent fumes that corrode aircraft structure and wiring. Knowing what acid is and where it lives in the aircraft helps a pilot understand preflight battery checks, the reason for sealed battery boxes, and why corrosion near a battery is taken seriously.
Intuition Check
Do not think of acid only as a laboratory chemical. In aircraft work, it may simply be the battery liquid you are being warned not to touch, spill, or ignore.
Example Sentence 1
The mechanic found acid stains on the battery box and inspected the surrounding structure for corrosion.
Example Sentence 2
Any acid spilled on the battery tray must be neutralized immediately to prevent corrosion.