I once researched this purely by trawling airline websites, getting application forms (the questions give an idea on how they assess), applying for positions and then attending assessment days & interviews. There are various companies which give you ideas on types of psychometric testing available, and various HR companies which will happy consult you on a recruitment process to fit your airline (for a ridiculous fee).
Best thing is to list everything you look for in a crewmember then find a way of putting as many of these measures into a test, either written, team orientated, mental, physical, or question based. Just remember it has to easy to monitor and measure the results against your original aims and objectives.