How soon before takeoff should a pre-takeoff contamination check be accomplished in ground icing conditions?

The correct timing for conducting a pre-takeoff contamination check in ground icing conditions is crucial for ensuring safety and performance during flight operations. Performing this check 5 minutes before takeoff is recommended because it allows for the most accurate assessment of any potential contamination on the aircraft's critical surfaces, such as the wings, tail, and control surfaces.

This timeframe strikes a balance: it is close enough to takeoff that any recent weather influence is taken into account, yet allows the crew adequate time to detect and address any issues related to ice or snow accumulation. If the check were conducted significantly earlier, there would be a risk that new icing conditions could develop that might not be detected, impacting the aircraft's performance during takeoff and climb.

Conducting the check too soon may not provide the current status needed, while waiting too long could lead to being rushed or missing an important observation. Therefore, the 5-minute guideline provides an effective window for ensuring safe operations in icy conditions.