Complex sentence: On the last day of the test, the aircraft (F-WWKH) was performing takeoff in critical weather conditions, which meant voluntary closing of a hydraulic circuit and blocking one of the motors in the engines.
Split into simpler sentences: On the last day of the test the aircraft (F-WWKH) was performing takeoff in critical weather conditions. Which meant voluntary closing of a hydraulic circuit and blocking one of the motors in the engines.