The Flight Engineer not only requires an understanding of aircraft systems but requires an understanding of met, performance, navigation and a myriad of other subjects which, when added together can be classed as airmanship. He has to be able to OPERATE the aircraft, learning a set of SOP's, as well as being able to carry out a variety of drills of varying importance when things go wrong. To make sure he can carry out these drills he has to be able to carry out multiple emergency drills in a serious of ever more demanding sims. It is this that takes time. He also has to keep an eye on ever younger and more enthusiastic pilots, which are let's face it the only thing on the aircraft likely to kill you. I have both fixed aircraft and flown aircraft and the differences are in outlook on what is and isn't acceptable would surprise you. Not one of us believe that we are better than GE's and not one of us believe that some GE's couldn't do the Flight Eng job but I can guarantee that not all GE's could and that those that could would require the full 6 months, if not longer.