One of the topics for English exam

Hello! This is one of the topics for my English exam. Please, correct my mistakes

English as an aviation language.
The language of aviation worldwide is English. Air traffic controllers dealing with foreign crews are supposed to show a certain minimum level of competency with the language in accordance with ICAO requirements. These requirements are described on the ICAO rating scale which includes 6 levels and 6 specific skills. These skills are fluency, vocabulary, pronunciation, structure, interactions and comprehension.
ATCs have to pass the ICAO English test every 3 years if they have Operational level 4; (have to pass English test) every 6 years if they've demonstrated level 5; and ATCs who have demonstrated language proficiency at level 6 will not be required to demonstrate one in the future.
In my opinion, strict requirements for English proficiency is to avoid miscommunication because it is a factor in over 70% of operational errors.

This is perfect Pavel,

There is one section which I feel can be safely left out (between the brackets). No problems at all.

Bob