Which icing intensity classification indicates that icing is perceptible with a significant accumulation rate?

The classification that indicates icing is perceptible with a significant accumulation rate is moderate. This intensity level describes conditions where icing is noticeable to pilots and can lead to a significant increase in ice accumulation on the aircraft. Pilots should expect to observe a considerable impact on the aircraft’s performance and may need to take corrective actions, such as activating de-icing systems or changing altitude.

In terms of context, light icing typically corresponds to minor accumulations that may not significantly affect the flight characteristics of the aircraft immediately. Trace icing indicates very minimal accumulation that generally doesn't require special handling by the pilot, as it may not even be perceptible. Severe icing represents a situation with extremely high accumulation rates that can pose serious risks, requiring immediate action, but it goes beyond the classification of moderate.

Understanding these classifications is crucial for pilots and air traffic control, as they inform decisions related to flight safety and operational procedures during icing conditions.