После when, as soon as, before, after, unless, while, once, immediately, until в придаточных предложениях времени будущее время не употребляется, так же как и в if clause First Conditional.
Future Simple заменяется на Present Simple, Future Continuous – на Present Continuous, Future Perfect – на Present Perfect.
The police will board the plane immediately the plane lands.
She’ll do it while you are waiting.
He will do it once you have asked him.
