Looking at the pass marks that CASA publishes, the other subjects have between 69% and 92% of candidates passing. The fact that Flight Planning has a published pass mark of 39% says there is something very wrong, particularly given that the helicopter version of the exam has 90% of their candidates passing the exam. Maybe its easier to get a helicopter ATPL and convert across to fixed wing? With the massive discrepancy in pass marks between subjects, and between helicopter and fixed wing versions of the same exam - which should be of approximately equal difficulty - it is clear there are problems with the CASA system.