The Civil Aviation Authority has tightened the rules on the standard of English expected from foreign trainee pilots.
There have been communication problems between students on solo flights and air traffic controllers.
"What we don't want to see is any form misunderstanding because of language difficulties and we want to ensure there is a common understanding so it doesn't lead to safety concerns," said authority spokesperson John McKinlay.
Flight instructors have been told to gather evidence about trainees' ability to speak English before they are allowed to fly solo.
Some air traffic controllers have been contending with students talking too fast, and say the standard of English among some trainees has been frustrating.
Students need to provide evidence that they can read, speak, understand and communicate in English.