A S/O is simply a first officer in training. As soon as you complete your type rating and line training (40sectors FO Fast Track / 120 sectors for Normal) you become a F/O. It's a strange designation because its not actually a permanent position, just a temporary one until you get cleared on the line. They only difference is that your training is longer than someone who joins as an F/O and your salary less. As soon as you clear your training your an F/O. It shouldn't really matter whether you join as an F/O or FTSO except that there's such a training backlog at QR right now that instead of being an SO for 3/4 months you'll be one for a year or maybe more, and it can affect you financially if you have kids etc.
Last edited by Airmann; 26th Jun 2013 at 10:55.