ICAO (International Civil Aviation Organization) has established language proficiency requirements for aviation personnel to ensure effective communication in English, which is the international language of aviation. These requirements are outlined in ICAO Annex 1 to the Convention on International Civil Aviation. The ICAO English language proficiency levels are categorized into six levels, ranging from Level 1 to Level 6.

1. Level 1 - Pre-Elementary:

1. Limited to no ability to use English for communication purposes.
2. Communication is very basic and may not be effective in routine or emergency situations.

2. Level 2 - Elementary:

1. Basic ability to communicate in routine situations.
2. Can handle a limited range of simple, isolated, and familiar tasks.

3. Level 3 - Pre-Operational:

1. Effective communication in routine and non-routine situations.
2. Can handle a variety of tasks related to both routine and non-routine circumstances.

4. Level 4 - Operational:

1. Effective communication in routine and non-routine situations.
2. Can handle a wide range of complex tasks and situations.

5. Level 5 - Extended:

1. Advanced proficiency in English communication.
2. Can handle a wide range of tasks and situations, including those that are complex and demanding.

6. Level 6 - Expert:

1. Near-native or native-level proficiency in English communication.
2. Can handle all tasks and situations, including those that are highly complex and demanding.

Aviation personnel, such as pilots and air traffic controllers, are required to achieve a minimum Level 4 proficiency in English to meet ICAO standards. Achieving Level 4 indicates that individuals have the necessary proficiency to communicate effectively in routine and non-routine situations in the aviation context.

It's important for aviation personnel to undergo language proficiency assessments to ensure that they meet the required standards. Training and language proficiency programs are often available to help individuals improve their English language skills to meet the ICAO standards.