Disciplines

Mechanical Engineering and Mechanical Engineering Technology, especially with an aerospace focus, are the disciplines that contribute the most to jet engines. As they are, at their core, an oversized and overpowered air compressor, mechanical engineers create and optimize every part of their design, from the compressor blades, to the combustion chambers, and the exhaust nozzle. Mechanical engineers are also the most involved discipline when it comes to designing the aircraft which the engines are attached to, or the systems that use jet engines as generators. Aerospace engineers in particular specialize in air and spacecraft, with subsets aeronautical engineering and astronautical engineering focusing on each division respectively.

Although computers were not yet invented when the first jet engines were created, they eventually became critical components in managing their internal functions. Just as cars began using computers to control fuel injection systems, jet engines began using computer-controlled fuel management, as well as controlling adjustments to physical parts such as variable pitch compressor blades and adjustable turkey feathers on the nozzles, and even eventually including thrust vectoring for increased maneuverability on newer-gen fighters. Most aircraft being produced now is also fly-by-wire, meaning that the plane's controls for throttle, control surfaces, landing gear, and more are all electrically controlled instead of mechanically and hydraulically adjusted like they were previously. This results in a complex web of wires running throughout the chassis of the aircraft, designed by electrical engineers to ensure that all systems are reliable and receive enough power. 

These disciplines are not as directly related to the engineering of jet engines as mechanical, electrical, and computer engineering, but at the end of the day these engineers are still critical to getting those engines to their end goal. Civil and construction engineers are responsible for the design and placement of the factories that the engines and aircraft are produced in, as well as the roads that the vehicles transporting the parts drive on and the airports and airbases where the aircraft reside and operate out of. Environmental engineering is more prevalent than you may expect, as the environmental impacts of airports are an ever-present concern, including jet engine emissions and societal issues such as airport noise and air traffic affecting some people.