What is the maximum allowable temperature for takeoff?

The maximum allowable temperature for takeoff is based on International Standard Atmosphere (ISA) conditions. The ISA defines a standard temperature at sea level as 15°C. Each increase in temperature above this standard affects aircraft performance, notably its ability to generate lift and its engine efficiency.

Selecting ISA +35°C means that for takeoff, the aircraft can operate at temperatures that are 35 degrees Celsius above the ISA standard. This reflects a maximum tolerance that takes into account various factors such as altitude, aircraft design, and the need for sufficient performance margins during takeoff.

Operating at ISA +35°C generally provides a wider margin for safe operations, as it acknowledges temperature variations that can occur in real-world conditions, especially in warmer climates or during summer months. Choosing a lower maximum temperature, such as ISA +30°C or below, could limit operational capabilities, particularly in regions where higher temperatures are common. Thus, the choice of ISA +35°C for maximum allowable takeoff temperature represents an industry-standard approach to ensuring safety and performance reliability of aircraft under varying thermal conditions.