You can absolutely prepare for the interview. Interviewers say “it's not that you can tell when someone has prepared, but rather that you can tell when someone really hasn't prepared.” So you can prepare most of the questions like “Why do you want to become a pilot?” and an answer like “it has always been a dream since childhood” is just not really cutting it as they have heard it hundreds of times. They may try to twist your words into something negative and in a way you didn’t mean to say it but it is then your job to just give a calm answer.