Hola Steve -
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JAR are pilot licences issued in Europe, includes UK... and FAA are pilot certificates issued in the USA. While both give same privileges, and are similar, there are notable differences in written exams theory subjects. The training in simulators is generally quite similar.
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If you wish to make a career in Europe, you better do the "JAR" training. The "FAA" training is directed for people living in the USA. Both have advantages and inconveniences. Doing one type of training, then converting into the other, is rather complicated and is somewhat expensive, particularly for holders of FAA certificates seeking JAR certification.
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Happy contrails