Definition
The standard rate at which temperature and pressure decrease with altitude in the International Standard Atmosphere. Temperature decreases at approximately 2 °C (3.5 °F) per 1,000 feet of altitude gained, and pressure decreases at approximately 1 inch of mercury per 1,000 feet, up to about 36,000 feet.
Plain English
It's the steady, agreed-upon rate at which the air gets colder and thinner as you climb. Aviation uses these fixed numbers as a baseline, even though the real atmosphere rarely matches them exactly.
Context Anchor
Seen in atmosphere, weather, performance, and instrument-flying discussions when comparing real outside air temperature to the standard reference atmosphere.
Derivation
Lapse' comes from the Latin 'lapsus,' meaning 'a slipping or falling.' Here it describes how temperature and pressure 'fall off' as altitude increases. 'Standard' signals that these are reference values, not what the air is actually doing on any given day.
Why Pilots Care
Pilots apply the standard lapse to estimate temperatures at altitude, which affects aircraft performance, engine operation, and density altitude calculations.
Analogy
Standard lapse is like a ruler for temperature with height. It gives you a normal reference line, so you can tell whether the real atmosphere is warmer or colder than expected.
Grounding Statement
If the air followed standard lapse, air that was 15 °C at sea level would be about 5 °C at 5,000 feet.
Intuition Check
“Lapse” does not mean a mistake or a delay here; it means temperature falling with altitude. “Standard” does not mean the real air must behave this way; it means this is the reference rate used for comparison.
Example Sentence 1
Using standard lapse, the temperature at 10,000 feet should be about 20 °C colder than at sea level.
Example Sentence 2
When actual temperatures deviate from the standard lapse, the pilot adjusts performance planning for takeoff and climb.