Iam Dip.in automobile engg. student. my aim is to go with B.tech Aeronautical engg. any options for iit or nit ?

I know there is less oppurtunities for aeronautical engineers.. as per aieee & iit -jee norms 3 or 4 diploma is also a eligilibilty but, some guyz say you cannot find the place in these reputed institutions.....if possible with these colleges what are the pattern of exam.pls mail me about this quer