How many total levels of English language proficiency are mentioned?

In the context of aviation and international standards, particularly pertaining to the International Civil Aviation Organization (ICAO), there are four defined levels of English language proficiency. These levels are categorized as Level 1 (pre-elementary), Level 2 (elementary), Level 3 (operational), Level 4 (extended), and Level 5 (expert), where only the first four are commonly referenced for compliance in aviation communications.

The inclusion of four levels allows for a structured assessment of a pilot's or air traffic controller's ability to communicate effectively in English, essential for safety and operational efficiency in international aviation. This structured categorization aligns with ICAO's emphasis on clear communication and the need for proficiency in English, particularly in situations where misunderstandings could lead to safety risks.

When considering the total levels of English language proficiency as applicable to civil aviation, it is clear why the four-level system is the correct answer.