ICAO Level 5
The "EXTENDED" level.
Most of the non-native English speakers simply don't qualify for a level 6.
If you still want to show the aeronautical community that your English skills are better than the lowest level, you should aim at level 5.
Give proof of your 'Extended' skills
The extended level (ICAO Level 5) fills the gap between the experts (level 6) and the basic operational qualities of level 4.
If you pursue a career in aviation, e.g. as an airline pilot, level 5 could be one way for you to give proof of your English language skills, even though you're not a native speaker.
The level 5 licence endorsement will be valid for 6 years and gives you more time before you need to come back to take the revalidation exam!
Your English language skills will be assessed
in the following areas:
No room for guessing.
A good English speaker can hear that it's not your mother tongue - but your English is so good that you barely cause any confusion when you speak.
Let's put it like this: the words sound like they should sound. But, with an accent.
You at least try the complicated sentences.
There's no doubt that your basic grammar skills are very good. But do you also try to form some more complex sentences? Longer ones? Multi-clause sentences? They don't always need to be correct - but at least you try.
It's a lot, and it sounds nice.
It doesn't take you long to find an answer for a question, unless you are suddenly confronted with a very odd or unfamiliar situation.
Basically, you know what a discourse marker is. You try to use some of them to make the things you say sound nice.
The right word for a lot of things.
Your vocabulary range - compared to your flight experience - is really good. You can't talk about unfamiliar things like biology, botany or medicine like a native speaker could, but you're able to do far more than just filing a flight plan and continuing to your destination.
Sometimes, you even use idioms.
Predictable and unpredictable situations.
It is fairly easy to understand things when you know what to expect. But you don't only understand the 'regular' and 'expected' stuff. You also have no problems understanding less predictable things.
Can you understand an English news broadcast?
More than only 'say again'
You're not only not afraid to ask say again if you didn't understand something - you actively strive for clarification and for communication.
You can initiate and lead a meaningful conversation.