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ISA Deviation

    ISA temperature deviation is now shown next to the actual temperature. Flying in ISA-plus temperatures can have a negative impact on performance.

    Consider the following example for Jundiai airport (SBJD). 

    ISA deviation is defined as: actual temperature – ISA temperature. 

    Standard sea level temperature is defined to 15°C (59°F) at MSL and decreases approx. 2°C per 1000 ft altitude. 

    In the example above the ISA temperature at 2484 ft is 10°C. 

    15°C – 2.484 x 2°C = 10°C; and then get the deviation: 24°C – 10°C = +14°C