Sir i can do BE in aeronautical engg. after diploma in mechanical engg.with 90%

Of course you can opt for lateral entry admissions after eligibility tests direct to second year of a B Tech Programme. Alternately you may pursue AMAeSI offered by Aeronautical Society of India considered equivalent to B Tech

Yes, you can do Mechanical Engineering with Aeronautics BEng. It will help you work with an aircraft or engine manufacturer or an airline, or to apply your specialised training to another high-technology industry.