FAA harder than JAR???
Are u sure about that? JAR is meant to be much much harder than FAA exams. So i don;t know how you could fail the easier exam. Another thing concerning ATPL subjects such as aerodynamics, aircraft general knowledge...the knowledge doesnt change over FAA and JAR, JAR is supposed to be more thorough that is all.
Also aerodynamics principles and aircraft general knowledge is not different in other parts of the world, air law maybe but otherwise i don't think so.
People with JAR only need to do air law in most conversion cases. However FAA people almost always need to do a 6 month conversion course.
newagebird