Image Credit: https://www.wired.com
A Flight Engineer (A&P Licensed) is part of the Pilot Crew of an airline. He is responsible for the monitoring and systems check of the aircraft on flight. He should be an Airframe and Powerplant (A&P) License Holder, factory trained and rated on the aircraft he flies with and preferably with flying background. As an example, Flight Engineer of an Airbus must be trained in their factory in France.
Airline Operations is totally different. It is more rigid because their planes fly all the time and log thousands of hours yearly.