As a training exercise only we had a TC who, in the sim, would give a simple start fault on #1 or #2, then we would proceed #3, normal start and so to #4, just as #4 lit up #1 would slowly start runaway up, (FCU fault), just to demonstrate the need for both pilots to monitor starts and don't forget the other engines which themselves have only just started and could be subject to a latent problem.