Complex sentence: The supplementary ventilation system was turned on and ran for seven minutes with the blades set incorrectly, until the blades were set correctly and the smoke cleared sufficiently for the passengers and crew to evacuate.
Split into simpler sentences: The supplementary ventilation system was turned on and ran for seven minutes with the blades set incorrectly. Once the blades were set correctly, the smoke cleared sufficiently for the passengers and crew to evacuate.