Definition
The temperature defined by the International Standard Atmosphere (ISA) as 15°C (59°F) at mean sea level, decreasing at approximately 2°C per 1,000 feet of altitude gain. It is the reference temperature used to calibrate altimeters, performance charts, and other aircraft instruments.
Plain English
The agreed-upon 'normal' air temperature at each altitude that engineers and instrument makers use as their baseline. At sea level, that baseline is 15°C, and it gets cooler as you go up. Real air is rarely exactly this temperature, but instruments are built assuming it is.
Context Anchor
Seen in altimeter error discussions, especially when explaining why indicated altitude can differ from the airplane’s actual height above the ground or sea level.
Derivation
Standard' comes from the Old French 'estandart,' meaning a fixed point or reference flag that others measure against. In aviation, standard temperature is exactly that — a fixed reference everyone measures real conditions against.
Why Pilots Care
Differences from standard temperature cause the altimeter to display an incorrect altitude, creating a safety risk during instrument flight.
Grounding Statement
On a very cold day, the altimeter may show a safe altitude while the airplane is actually lower than that indicated altitude.
Intuition Check
Standard does not mean the outside air is required or expected to match this temperature. It means the fixed reference temperature pattern used for altimeter calculations.
Example Sentence 1
On a cold winter day, the outside air was 20°C below standard temperature, so the pilot applied a cold-weather altitude correction before crossing the mountains.
Example Sentence 2
The pilot checked standard temperature values to determine the expected altimeter error before entering the clouds.