All three hydraulic systems on the Air India flight from Thailand’s Phuket to Delhi that dropped 300 feet, briefly failed, leaving the aircraft without elevators and ailerons for 4 seconds, a preliminary report by Airbus has found.An inside view of the Air India flight from Phuket to Delhi after it hit turbulence, injuring a number of passengers, in New Delhi. (ANI)According to the report, the co-pilot of the flight AI2379 applied full nose-down input, but the controls initially did not respond. The hydraulics then recovered after the brief problem, it said, adding that the root cause of the issue is still unknown.On August 4, the Phuket-Delhi flight AI2379 dropped 300 feet in a sudden loss of altitude during cruise, injuring 20 passengers and four crew members. An initial statement from Air India had cited turbulence as the reason.The report from the French aircraft manufacturer stated that the aircraft's hydraulic pressure was lost. After that, it lost the flight-control actuators and then the elevators, also known as ailerons or spoilers, became unavailable. The aircraft's pitch changed, and the autopilot disconnected. The first officer, who was the pilot flying the aircraft, then applied nose-down input, which caused the flight controls to recover when hydraulic pressure returned, it added.