Which are the best institutes to pursue course in the field of Aviation after completing Diploma in Electrical Engineering?

Since you have completed Diploma in electrical engineering,i would advise you to continue with your job and opt for a distance course in aviation. There are many universities like CCE, Dehradun which offers distance bachelor and masters degree in aviation.these courses will earn you a degree and job

Aviation refers to all activities involving the operation of aircrafts. Aviation courses in India deal with Flying Operation (jobs performed by Pilots), Aircrew (such as Air Hostesses), Aircraft, Air Traffic Management, Technical aspects of Flight, Aviation Safety, Regulatory Policies and economics