In which class of airspace must two-way radio communication be established with Air Traffic Control before entering?

The requirement for two-way radio communication with Air Traffic Control before entering specific airspace is a crucial aspect of controlling traffic and ensuring safety. Class C airspace is characterized as having a surrounding airport with a control tower and usually has a significant volume of air traffic. Thus, for pilots operating in this airspace, establishing two-way radio communication with Air Traffic Control is essential before entering. This communication allows pilots to receive important information about traffic, weather, and other factors that could affect flight operations in that busy environment.

In contrast, Class E airspace may not require two-way communication unless specified, and Class G airspace is uncontrolled, meaning that there is no requirement for communication with Air Traffic Control. Therefore, the correct answer highlights the necessity of maintaining communication in more structured and dense airspace, such as Class C, to promote safety and coordination.