Flight MU5735 Crash Theory: Pilots Likely Became Unconscious During Steep Descend, Expert Says

As the aviation industry tries to unravel the mystery behind the China Eastern Airlines Flight MU5735's nosedive crash, an expert has said the pilots may have already become unconscious during the steep descend.

The Boeing 737-800 aircraft's crash was reportedly very unusual for it being vertical, Hu Xiaobing, a professor at the School of Safety Science and Engineering of the Civil Aviation University of China, told CGTN.

Many reasons -- such as technical failures like engine malfunction, airplane body structure damage, or even bird strike -- may have led to the passenger jet's steep descent. Human factors such as pilot error or an external attack could also have caused the crash.

However, the exact reason why the airline crashed, while en route to Guangzhou after taking off from Kunming, in the southwest, will be known only after data from the black boxes are retrieved.

Search teams Wednesday found one of the black boxes, which was later believed to be the cockpit voice recorder (CVR). Hu said the CVR will be able to provide clues to the cause of the crash as it records conversations.

Head of the aviation safety office of the Civil Aviation Administration of China, Zhu Tao, told reporters the exterior of the black box had been severely damaged, but its data storage unit was relatively complete despite the damage. The device was being sent to Beijing for decoding.

Hu also said if the crash was caused due to a technical failure, the flight data recorder -- the black box yet to be found -- could shed light as to what might have happened as it records many important data about on-board equipment.

The search area had been expanded Thursday to find the second black box. Recovery teams in China have found part of an engine and other larger pieces of debris, including a white wing section with the red and blue China Eastern logo on it.

So far, no survivors have been found among the 132 people on board the ill-fated plane.

Flight data revealed the plane plunged out of the sky at close to the speed of sound before slamming into the mountain, causing a fire. The plane was cruising at 29,000 feet when it suddenly nose-dived. The flight data provided by an air traffic monitoring service revealed the plane pulled out of the first dive before another sent it crashing into the ground.