Under what conditions is a pre takeoff contamination check required?

• A. OAT less than 5 C and visible moisture present
• B. OAT greater than 30 C
• C. OAT less than -5 C and no moisture
• D. OAT equal to 5 C and visible moisture

Answer: (A)

The key idea here is when ice or other contamination on the aircraft surfaces can re-form or remain after de-icing in cold, moisture-present conditions, so a pre-takeoff check is necessary to verify the surfaces are clean before flight.

A pre-takeoff contamination check is required when the outside air temperature is below 5 C and there is visible moisture present (such as clouds, fog, rain, sleet, or snow). In these conditions, moisture can quickly re-freeze on the aircraft, potentially recontaminating critical surfaces after de-icing, so a check ensures the contamination has been removed and the aircraft is safe to take off. If either condition isn’t met—warmer temperatures, or no visible moisture—the likelihood of problematic re-contamination is much lower, so the check isn’t required.

So, the given condition—outside air temperature below 5 C with visible moisture—fits the rule for needing the pre-takeoff contamination check.