Definition
The modern, internationally agreed system of measurement, abbreviated SI (from the French Système International d'Unités). It defines a coherent set of base units — including the metre for length, kilogram for mass, second for time, ampere for electric current, kelvin for temperature, mole for amount of substance, and candela for luminous intensity — together with derived units built from them, such as the newton, pascal, joule, and watt.
Plain English
SI is the worldwide standard system of units used in science and engineering. It is the metric system in its formal, modern form, with a fixed set of base units that nearly all countries and technical fields use.
Context Anchor
Seen in aviation weather, aircraft maintenance, engineering data, performance information, and international aviation references when measurements are given in metric-based units.
Derivation
From the French Système International d'Unités, meaning 'International System of Units,' adopted in 1960 by the General Conference on Weights and Measures. The abbreviation SI comes from the French word order, which is why the letters appear reversed compared to the English name.
Why Pilots Care
Allows accurate calculations and data sharing on international flights without conversion mistakes that could affect weight, fuel, or performance figures.
Intuition Check
Do not read “international” as meaning every country or every aviation document uses only these units. Here it means a shared standard measurement system that many technical references use, even though aviation often still mixes unit systems.
Example Sentence 1
The aircraft's European maintenance manual listed all torque values in International System of Units, so the mechanic converted newton-metres to foot-pounds before tightening the bolts.
Example Sentence 2
When planning a trip to Canada the pilot converted fuel loads using the International System Of Units to match the airport's metric fuel truck readings.