Complex sentence: When the pilot ejected the seat would leave the aircraft and a drogue parachute would slow the seat and deploy the blades within four seconds, it would take two more seconds for the turbofan to run up to full power and the seat becomes a gyroplane.
Split into simpler sentences: When the pilot ejected the seat would leave the aircraft and a drogue parachute would slow the seat and deploy the blades within four seconds. After an additional two seconds, the turbofan would run up to full power and the seat would become a gyroplane.