A flight engineer specializes in the mechanics and maintenance of aircraft. Applicants for this license (certificate) need to prove their knowledge by passing a written flight-engineer test and must meet several other miscellaneous requirements.
A flight engineer must be at least 21 years old. All applicants must also be able to read, write, speak, and understand the English language.
The general rule is that these mechanics also need a second-class medical certificate. This certificate must be obtained within the 12 months preceding the application for a flight-engineer license. Ask your aviation mechanic school or employer about how to get a medical certificate.
There is also required flight training for flight engineers. You may take the exam before the flight training, but the general rule is that you have two years after that flight training to pass the exams.
There are multiple types of experience that will qualify a mechanic to be a flight engineer. They include having a commercial pilot certificate with an instrument rating and 5 hours of flight-engineer training. Of course, not all engineers are pilots. You may also qualify by taking a 2-year course specifically designed for training of aircraft and aircraft-engine maintenance (and 5 hours of flight-engineer training). 3 years of experience is also sufficient as the experience for an FAA flight-engineer license.
Those with aeronautical, electrical, or mechanical engineering degrees need only 6 months of experience plus the flight-engineer classes.
Other qualifying experience is 100 hours of flight time as a flight engineer, 200 hours as pilot in command (or second in command performing pilot-in-command duties while supervised) of a transport-category airplane, and completion of a flight-engineer ground and flight course within 90 days before the certificate application date.
There are some good information on the Pprune forum, and if you do your research and have some more specific questions there will be people on there with years of experience who will be prepared to help you.. Also you can find some useful info on www.flyaeroguard.com/programs/rotor-transition-program/