Complex sentence: For pilots, the next step was Flying Training School (FTS) using Harvard aircraft, then training on T-33 jet trainers, Beechcraft Expeditors, or Mitchells at an Advanced Flying School (AFS).
Split into simpler sentences: For pilots, the next step was Flying Training School (FTS) using Harvard aircraft. Training continued on T-33 jet trainers, Beechcraft Expeditors, or Mitchells at an Advanced Flying School (AFS).