What Is Standard Temperature in Aviation?

The International Civil Aviation Organization (ICAO) created a standard temperature for aviation in order to establish a baseline from which manufacturers could develop performance data usable for pilots around the globe. This standard temperature is referred to as “ISA,” or the ICAO Standard Atmosphere. Keeping this aviation standard temperature allows for pilots and crews to more safely navigate the skies without unexpected weather hazards. While weather can always bring surprises, being able to properly calculate the conditions often helps you to stay ahead. 

The standard temperature in aviation is measured at the mean sea level (msl) pressure of 29.92 inches of mercury (Hg) and is 15° C or 59° F. The standard temperature decreases 2 °C or 3.5 °F for every 1,000 feet gained, and this is reasonably accurate up to 36,000 feet msl. From 36,000 feet to 80,000 feet msl, the temperature zone is considered constant around –55 °C or –65 °F. 

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How To Calculate Standard Temperature in Aviation

Calculating the standard temperature in aviation is actually an easier process than many beginner pilots may think. The standard temperature lapse rate means the temperature is decreasing at a rate of 2° C or 3.5° F per thousand feet gained. This holds true up to 36,000 feet msl. So, while your standard temperature at msl is 15° C or 59° F, your standard temperature at 20,000 feet msl will be -24.6°C or -12.3°F.  

Temperature and pressure changes can greatly affect your plane and its performance. Knowing how to properly calculate the standard temperature in aviation can help you keep your plane performing at its best while enjoying every flight. 

How Does the Temperature Affect Aircraft Performance?

Temperature can greatly affect the performance of an aircraft during takeoff, landing, and in flight. Not only can the aircraft’s engine performance be affected, but the aerodynamics involved with flying can vary as well. This is where density altitude and  additional altitude definitions are important to know about anytime you fly. 

The FAA defines density altitude as pressure altitude corrected for nonstandard temperature variations. Air density decreases with altitude. Air density also decreases as the temperature increases. Both of these factors can cause several things in an aircraft to register a drop in performance, including your engine, wings, and propeller(s).  

What Is Standard Temperature Lapse Rate in Aviation?

The standard temperature lapse rate in aviation is how you can easily calculate the standard temperature, no matter the altitude. From sea level up to 36,000 feet msl, the temperature will likely decrease at a rate of  2° C or 3.5° F for every 1,000 feet gained. At 10,000 feet msl, there will be a standard temperature of -4.8° C or 23.3° F. Keep in mind at sea level, the standard temperature is 15° C or 59° F.

What Is Standard Temperature and Pressure in Aviation?

Because the atmospheric pressure directly affects the standard temperature in aviation, it’s important to know about standard pressure in aviation, as well. Standard air pressure at sea level averages 29.92 inches of Hg (mercury) or 1013 millibars. This means that when measuring it at sea level, the atmospheric pressure will force the mercury in a barometric gauge to rise to a height of 29.92 inches. The varying atmospheric conditions led the ICAO to create the standard pressure in addition to the standard temperature. 

What Is the Difference Between Standard Temperature and Pressure and Standard State?

Standard temperature and standard pressure in aviation are both different measurements used to refer to the atmospheric conditions, but they both directly affect each other. As your atmospheric pressure decreases, so will your temperature. Measured at sea level, your standard temperature is 15° C or 59° F and your standard pressure is 29.92 inches of mercury. The standard state temperature and pressure are referred to as STP. Just as pilots want a base reference point for atmospheric conditions, scientists want the same simplicity when gases are involved. The standard state temperature is 0° C or 32° F while the standard state pressure is 10⁵ Pascals. 

What Is the Relationship Between Altitude Air Density and Temperature?

Both temperature and pressure will decrease as altitude increases. Because the density of the air will decrease as you gain altitude, the ambient density altitude and pressure altitudes are both important things to consider when flying.  

Example of the Effects of Temperature on Aircraft Performance

A fairly simple way to understand the effect temperature can have on the performance of your aircraft is to think of how your aircraft flies at higher altitudes. The higher the altitude, the less dense the air is and the less efficiently your aircraft can operate. High temperatures can deliver the same effects and cause your aircraft to lose performance.

The 3 Factors That Affect Density Altitude

The three main factors that directly affect density altitude are altitude, temperature, and humidity. It’s important to consider that density altitude is really the altitude that your airplane seems to be flying at. This means you are simply correcting the pressure altitude based on the varying temperatures and humidity. 

Altitude

The higher you fly, the less dense the air is. When the air is less dense, it means there are fewer molecules within a given volume of air, including oxygen and nitrogen of which the Earth’s atmosphere is composed. The thin air at high altitudes can result in your aircraft engine performing less efficiently, which is a critical thing to consider before you fly out of high-elevation airports. 

Temperature

Similar to higher altitudes, higher temperatures lead to less dense air as well. If the temperature goes above the standard temperature, the air density decreases. This delivers the same poor performance issues as high altitude, meaning your engine, propellers, and wings will likely all be operating less efficiently. 

Humidity

Altitude and temperature are the greatest factors to consider before you fly, but humidity is as well. High humidity and temperatures can cause the atmosphere to hold a high amount of water vapor. This can play a major role in how your engine will perform. While high humidity has a small effect overall, it can occur and should always be kept in mind. 

Standard Temperature vs. Pressure

When atmospheric pressure is concerned, it’s important to know that both your standard temperature and standard pressure will decrease together. As these different values measure the atmospheric conditions, knowing how to adjust for the changes at varying altitudes is essential for safe flying. 

Safely Navigate the Skies at Any Altitude! 

Both new pilots and the most experienced can benefit from knowing the standard temperature in aviation and how it can affect your flights. There are a variety of tools and apps available to help you determine the specific temperatures and pressures at your departure and destination airports, as well as en route. Verifying any changes in temperature or pressure during preflight can allow you to adjust in a way that will keep your flight running smoothly, from takeoff to landing. While the standard temperature and pressure won’t change, techniques to keep yourself ahead may. You can find up-to-date flying tips and techniques in FLYING Magazine. Subscribe today!