Hey Mayank! Aerospace engineering is the primary field of engineering concerned with the development of aircraft and spacecraft. It has two major and overlapping branches: aeronautical engineering and astronautical engineering. Avionics engineering is similar, but deals with the electronics side of aerospace engineering. For IAF you need to be eligible according to the criteria as IAF conducts Indian Air Force Aeronautical Engineering Exams. In Indian Air Force Aeronautical Engineering is divided into two branches - Mechanical and Electrical. Aeronautical Engineers in the Mechanical Branch are responsible for aircraft and its weapon system. They are concerned with the operational readiness of aircraft.