Chinese investigators have disclosed that the Sichuan Airlines Airbus A319 which lost a main cockpit window at cruise altitude also suffered substantial damage to its flight-control unit.
The aircraft had been cruising at 9,800m at the time of the 14 May accident, states French investigation authority BEA, citing its Chinese counterparts.
It states that the entire right-hand windshield pane separated, damaging the flight-control unit and causing the aircraft to depressurise.
The flight-control unit, located on the upper forward instrument panel, features dials and switches that enable the crew to relay altitude, heading and other instructions to the autopilot.
Oxygen masks were deployed in the cabin after the windshield loss, says BEA, and the crew transmitted a distress call, setting the transponder to the urgency squawk code 7700.
The aircraft, bound for Lhasa, diverted to Chengdu, bursting two main landing-gear tyres on touchdown.
Civil Aviation Administration of China says its south-western bureau is investigating the event, adding that it has already issued an emergency safety notice detailing the incident and outlining a number of safety instructions.
It says operators should be "highly vigilant" in assessing the safety risk, and that components with relevant part numbers should be checked. Flight crew should "strictly follow" operating manuals and cabin crew, in particular, should remind passengers to fasten seatbelts, it adds.