An aeronautical engineer must have a solid foundation in basics of A/C System, the principle of cooling and sound knowledge of the way the principle is applied to various systems used in the A/C. The various systems that exist in aircrafts are as follows Hydraulic System Aircraft Oxygen System Pneumatic System Air-conditioning and Pressurization System Electrical System Engine oil & Fuel System Aircraft Instrument System Ice and rain protection system Fire protection and smoke detection system Leak and Waste system Aircraft weapon (Rocket, Gun, Missiles, Bomb& Ejection system) Communication and navigation system Propulsion system