To apply for the B.Tech in Aeronautical Engineering at FIAME, Sonipat, candidates must first ensure they meet the eligibility criteria, which include passing 10+2 with Physics, Chemistry, and Mathematics. The application process involves filling out the application form available on the FIAME website, uploading required documents, and paying the application fee. After submission, candidates may need to appear for an entrance exam or interview. Successful applicants will receive further instructions regarding admission procedures.