What corrective action must pilots take when temperature is at ISA -15°C for the DA?

When the temperature is at ISA -15°C, it indicates that the actual temperature is significantly lower than the standard temperature at that altitude. This situation affects the Density Altitude (DA), which is an important factor in aircraft performance calculations. At lower temperatures, the air is denser, which generally means that the aircraft will perform better than what the current elevation might suggest.

To achieve accurate calculations for performance, pilots need to adjust their altitude based on these temperature deviations using correction charts. These charts provide specific adjustments to be made based on the actual temperature compared to the standard atmospheric conditions (ISA). By using the correction charts, pilots can determine the actual density altitude and make any necessary adjustments to ensure safe operations, including takeoff distances and climb rates.

Thus, the proper corrective action in this scenario is to utilize the correction charts to account for the temperature deviation from ISA standard conditions, leading to accurate aircraft performance data.