S/O vs F/E.
I believe what is confusing a lot of people is the term used to describe the systems panel operator on L-1011(TriStar) 727,707,DC8 etc. The individual is not controlling (flying)the A/C. He/she is actually carrying out the function of a flight engineer. Some airlines(including mine) hire pilots and train them (and licence them) to operate the panel so to recognise this they call them pilot engineers (P/E) or third pilots(P3) or a second officer(S/O). Whether the crew member has a flying background or not he is performing the function of a flight engineer. So to sum it up.....S/O, P3 or third pilots are actually flight engineers, what they are called is academic. The individual is operating on a flight engineer's licence and not a pilot's licence.