What temperature adjustment is required if the temperature is less than ISA -15°C?

When the temperature is less than ISA -15°C, the atmospheric performance of the aircraft can be impacted significantly. In such conditions, the density of the air decreases, leading to a higher density altitude (DA).

If the air temperature is lower than the International Standard Atmosphere (ISA) conditions, corrections must be made to the calculations for takeoff, climb, and landing distances, among other performance-related factors. Specifically, when the temperature drops below ISA -15°C, it is essential to add a correction factor to account for the difference in density altitude caused by the cool air. This will help to ensure that the aircraft operates within its optimal performance parameters, allowing for safer and more efficient flight operations.

The need to add correction is vital for pilots during flight planning and execution, as failing to account for temperature effects can lead to performance degradation, affecting the safety and efficiency of the flight. Therefore, the correct action in this scenario, where the temperature is specifically below ISA -15°C, is to make the required adjustment to the density altitude calculations.