Question

Está certo falar "He is at the airport" ao invés de "He was at the airport" ?

Answer 1

Não é correto, porque "He is at the airport" está no presente. É equivalente a "Ele está no aeroporto". Enquanto que "He was at the airport" está no tempo passado e é equivalente a "Ele estava no aeroporto".

PRESENTE:

I am
You are
He / She / It is
We are
You are
They are

PASSADO:

I was
You were
He / she / it was
We were
You were
They were

Answer 2

está certo nas duas formas mas elas são usadas de modo diferente:

"He is at the airport" "Ele esta no aeroporto" = forma do presente, o que está ocorrendo agora. e
"He was at the airport""Ele estava no aeroporto" = forma do passado, o que já aconteceu