What is ACC in Aviation? (Altocumulus Castellanus)

Altocumulus Castellanus (ACC) is a type of cloud formation with a unique appearance that aviators need to be aware of. Understanding aviation terminology is essential for anyone who wants to get into aviation or work in the industry. For pilots, cabin crews, air traffic controllers, and aviation enthusiasts, Altocumulus Castellanus clouds are a common sight in the sky. Read on to learn more about this unique type of cloud.

What is Altocumulus Castellanus (ACC)?

Altocumulus Castellanus, also known as ACC, is a mid-level cloud formation found at an altitude of around 6,500 to 20,000 feet. ACC clouds are usually associated with the approach of a thunderstorm or other convective weather patterns. They appear as a layer of clouds with a series of vertical projections or turrets that resemble the battlements of a castle. The castellanus name comes from this unique appearance, which makes them stand out from other clouds.

Altocumulus Castellanus clouds are caused by rising columns of warm, moist air that lift the air in the atmosphere to its dew point, which then condenses into a cloud. The vertical projections observed within the cloud indicate that the air within the cloud is unstable, which means there is a strong likelihood of turbulence within the cloud layer. This makes them important for pilots to identify and avoid if possible.

Why is Altocumulus Castellanus Important for Aviation?

One of the primary reasons Altocumulus Castellanus is important for aviators is that it is often a sign of changing weather patterns, particularly thunderstorms, which can present a danger to aircraft. These clouds can signal that there is a high likelihood of turbulence and other convective weather concerns in the area, making them a critical factor in pre-flight planning and decision-making for pilots.

As Altocumulus Castellanus clouds can appear at any time of the day, especially during the summer months, when convective weather is more prevalent, aviation professionals need to be constantly aware of their presence. Pilots must avoid flying through these clouds whenever possible, as turbulence can cause crew and passenger injuries, damage to the aircraft, and even loss of control of the airplane.

How to Identify Altocumulus Castellanus?

Identifying Altocumulus Castellanus clouds requires a keen eye and knowledge of cloud formations. It helps to have a good understanding of aviation terminology and the difference between various types of clouds. ACC clouds are distinguished by their unique appearance, with vertical turrets or castles, and their mid-segment placement in the sky.

One way to distinguish ACC clouds from other types of clouds is to look for vertical growth formations, which stand out from flat or level clouds. Pilots can also identify ACC clouds using onboard weather radar or the Flight Information Service (FIS), which provides weather updates on aviation routes. Aviation professionals can use modern technology to identify and track weather patterns and alert pilots of any upcoming changes, including the appearance of Altocumulus Castellanus clouds.


Altocumulus Castellanus clouds are a common sight in the sky and an essential part of aviation weather forecasting. Understanding the unique appearance of ACC clouds and their significance to aviation professionals can help provide a safer flight experience for both crew and passengers. Pilots and other aviation professionals must remain vigilant when it comes to these clouds, as they are often a sign of changing weather patterns and the approach of thunderstorms or other convective weather-related concerns. By staying informed and knowledgeable about cloud formations, Aviators can help ensure a safe and secure journey for all.

Keywords: Altocumulus Castellanus, aviation terminology, ACC clouds, cloud formations, thunderstorms, convective weather patterns, pilots, Flight Information Service (FIS), aviation weather forecasting, mid-level cloud formation.

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