What action should you take during a walk-around inspection if you notice frost on the engine nacelle?

In the context of a walk-around inspection, noticing frost on the engine nacelle raises concerns about the aircraft's readiness for safe flight. The most logical action to take is to contact maintenance for advice. Frost on the engine nacelle may indicate that other critical areas of the aircraft, such as the wings and control surfaces, could also be affected.

Choosing to enter the plane to view the top of the wings may not address the immediate concern, as the frost on the engine nacelle could interfere with engine performance and overall safety. Maintenance personnel are equipped with the necessary expertise to assess the situation properly, recommend appropriate de-icing procedures, and determine if it's safe to proceed with the flight. Addressing such conditions is crucial for ensuring the safety and effectiveness of the aircraft before takeoff.

In summary, contacting maintenance is the most appropriate response to ensure that all factors affecting the aircraft's performance are thoroughly evaluated before making any decisions about flight readiness.