I found most of the ATPL’s (except Comms) challenging in different ways.
I have listed them in order of how challenged I felt in preparing for each exam.
Flight Planning
G. Nav
Met
Performance
Principles Of Fright
Air Law (How Interesting!)
Instruments
R. Nav.
Operational procedures
Human Perf.
Aircraft Gen.
Mass & Balance
Comms
I and many of my fellow class mates found flight planning tough, you can pass as most of us did with almost full marks but you really must ensure there are no questions types you are not familiar with and do all the feedback you can get hold of. Failing that work through all, yes all of the Bristol online questions in order and ensure you can do 60 flight planning questions in less than two hours! You get three hours in the real exam but I found it was the quickest three hours in my life, seemed like 40 mins at the time - who said time flys when you are having fun!
General Nav - I had been warned about this subject before I ever picked the book up so was worried about it from the start, again time goes quickly but I found it OK with most of the syllabus covered but questions mainly more straight forward than I had prepared for.
Met - I was disappointed with the exam as the questions were mainly global climatology based with only one or two on icing, thunderstorms etc. Massive subject which you could spend years looking at on its own.
I found the graphs in Plight Planning & Performance hard work especially under pressure, again do as many As you can get hold of.
You can know the subject inside out but you really need lots of practice in how questions are asked and are quick in your decision on how to tackle the question and stick with your first answer.
I found studying until I lost them will to live did the trick! Study technique is key to these exams.
Good luck to all of you.
Cheers………