Which of the following is NOT one of the four intensities of structural icing?

The correct answer, "Extreme," is not recognized as one of the four standard intensities of structural icing. The National Weather Service and aviation guidelines define the intensities of structural icing as light, moderate, severe, and extreme is simply not part of that classification system.

Understanding the correct classification of icing is critical for aviation safety, as each intensity level has specific implications for aircraft operation and risk management. Light icing typically has minimal impact, while moderate and severe icing conditions can significantly affect aircraft performance and pilot decision-making. Knowing these classifications helps pilots and air traffic controllers assess weather conditions and make informed operational choices.