What does the abbreviation ISA stand for in aviation?

The abbreviation ISA stands for International Standard Atmosphere. This concept is vital in aviation as it provides a standard reference for various atmospheric conditions, including temperature, pressure, and density at different altitudes. The ISA serves as a baseline for calibrating aircraft performance, ensuring that pilots and engineers have a common understanding of how performance may vary with altitude and atmospheric changes.

In practical terms, the ISA is based on certain assumptions: a sea-level temperature of 15 degrees Celsius, a pressure of 1013.25 hPa (hectopascals), and a temperature lapse rate of 6.5 degrees Celsius per kilometer until reaching the tropopause. Understanding the ISA helps pilots in flight planning, altitude adjustments, and in understanding how their aircraft will perform under various environmental conditions.

The other choices, while they may sound plausible, do not accurately represent established terms in aviation, which is why they do not fit with the standard definitions used in the industry.