Three - I'm not so sure about MPLs. Flying airliners is pretty simple and most teenagers could pick up the flying bit with ease. On the flying side, the most awkward bit is dealing with the niff-naff and trivia. Writing legibly in small boxes is also a challenge to many. But the most difficult bit, which is certainly not covered when you knock a hole in the sky with a PA28 or something equally exotic, is where you are going to point your airliner and why. ie. it's the operation of the thing the really matters. Quite what single engine flying has to do with modern airline flying is beyond me. But the miss-match of training and functions doesn't end there. The full time zero-to-F/ATPL course doesn't really prepare you for a GA career either - it appears to be geared towards an airline career.