ICAO requires that language skills of pilots and controllers rated at Level 4 are re-assessed every four years, Level 5 pilots and controllers - every six years, while at Level 6, no further assessment of English language skills is deemed necessary.

The Level 4 (operational) proficiency is considered as a minimum ‘stepping stone’ to higher levels. The main benefit of high international standards of aviation English is that communications between aircraft crew and controllers are fully understood, particularly when non-standard words and phrases are used. In addition, improved language skills could help increasing the situational awareness of flight crews in relation to other aircraft, both in the air and on the ground.

Note: Commission Regulation (EU) 2015/340 states that the validity of the language proficiency endorsement for expert level (level six) is nine years from the date of assessment, for the English language. This provision is applicable for air traffic controllers in the EU member states