Sea-Level Standard Atmosphere (SLSA)

Overview

The Sea-Level Standard Atmosphere (SLSA) is a hypothetical model representing the Earth's atmosphere at sea level, defining standard values for pressure, temperature, and density. It is not a real-time depiction but a reference used for calculations and comparisons in aviation and engineering.

Standard Values

• Temperature: 15°C (59°F) or 288.15 K
• Pressure: 101,325 Pascals (1013.25 millibars or 760 mmHg)
• Density: 1.225 kg/m³

Purpose

SLSA is used for a variety of applications:

• Pressure altimeter calibrations
• Aircraft performance calculations
• Aircraft and missile design
• Ballistic tables
• Aviation standards and flying rules

Historical Context

Early Development (1920s)

The concept emerged from international agreements made in the 1920s.

U.S. Standard Atmosphere (1958)

First published by the U.S. Committee on Extension to the Standard Atmosphere. It has been updated in 1962, 1966, and 1976.

International Standard Atmosphere (ISA)

Developed by the International Civil Aviation Organization (ICAO), the ISA defines atmospheric properties with altitude at mid-latitudes.

ICAO Standard Atmosphere (1993)

Extended the altitude coverage to 80 kilometers and formalized in ICAO Doc 7488-CD.

Current Use

The 1976 U.S. Standard Atmosphere and the ISA are the primary standards in aviation today.