Definition
A unit used to express the relative intensity of sound or the ratio between two power, voltage, or signal levels on a logarithmic scale. In aviation maintenance, decibels (dB) are most commonly used to measure sound pressure levels, such as engine or shop noise, and to express gain or loss in electrical and avionics systems.
Plain English
A way of measuring how loud something is, or how much stronger or weaker one signal is compared to another. The scale grows quickly, so small number changes can mean large changes in loudness or signal strength.
Context Anchor
Seen in aircraft noise, engine run-up areas, hearing protection guidance, and maintenance shop safety discussions.
Derivation
From 'deci-' (Latin decimus, meaning one-tenth) and 'bel,' a unit named after Alexander Graham Bell. A decibel is one-tenth of a bel. Knowing this helps explain why dB values are small numbers that still represent large differences -- they are a compressed, logarithmic scale.
Why Pilots Care
Determines required hearing protection and verifies compliance with noise exposure limits to protect hearing during ground operations and maintenance.
Analogy
Decibels work more like steps on a steep hill than marks on a ruler. Moving up a few steps can put you much higher, even though the number did not change by much.
Grounding Statement
A normal conversation is around 60 dB, a busy ramp can exceed 100 dB, and a turbojet at takeoff power can reach 140 dB or more -- well above the level that causes immediate hearing damage.
Intuition Check
Do not read decibels as a simple straight-line count. A sound at 90 decibels is not just a little more intense than a sound at 80 decibels; the decibel scale grows by ratios.
Example Sentence 1
The technician wore hearing protection because the engine run-up area measured over 110 decibels.
Example Sentence 2
The maintenance manual specifies maximum decibel levels for safe operation of pneumatic tools in the hangar.