(Bloomberg) -- Chinese authorities said they need more time to determine why a China Eastern Airlines Corp. jet speared into a hillside a year ago, killing all 132 people on board, months after preliminary evidence suggested the pilot intentionally crashed the plane.

The probe into the incident involving the Boeing Co. 737-800 is continuing, the Civil Aviation Administration of China said late Monday, citing the complexity and unusual nature of the crash. More analysis is required, the regulator said. 

The aircraft’s two black boxes, which provide crucial information for investigators, were located shortly after the plane went down in southern China on March 21, 2022. While it can take months or years to pinpoint the cause of a crash, there were early indications a pilot took down the China Eastern plane in a murder-suicide, a person familiar with the probe said in June.

International conventions call for a final report into aviation incidents to be publicly released within 12 months of a crash, if possible. It’s not unusual for final reports to be delayed, especially when aircraft can’t be traced or if they’re submerged deep underwater. 

Some investigations, aided by plane and engine makers, have met that deadline, especially if the black boxes are found quickly. 

The China Eastern jet was flying level at a cruising altitude of 8,900 meters (29,000 feet) when it suddenly dropped, according to the CAAC. Video images show it hurtling nose-down toward the ground. The jet disintegrated on impact, the CAAC said previously. 

Lengthy Probes:

“Even though the flight recorders were located soon after the accident, there may have been some delay in recovering information as a result of significant damage or fire,” said Joe Hattley, a former aircraft accident investigator who worked on the disappearance of Malaysia Airlines Flight 370 in 2014. He now teaches the subject at UNSW Sydney’s School of Aviation. 

“For a major accident, you can expect anywhere between one to two years for the final report. It all depends on the complexity of the investigation,” Hattley said.

The final report into one of the most well-known incidents of pilot murder-suicide — the crash of a Germanwings GmbH plane in March 2015 — was released within a year. 

The cockpit voice recorder made it clear the copilot had locked the captain out of the space and deliberately flew the jet into the ground. It slammed into the side of a mountain in France, killing all 150 on board.

The China Eastern crash occurred with relations between Washington and Beijing at their lowest ebb in years. The crash of a US-made plane run by a Chinese, state-owned airline made the two rivals reluctant bedfellows in the investigation. Now, not everyone is happy with the information being released by the China’s aviation regulator. 

“It is both surprising and shocking that the CAAC has yet to come out with the investigation report,” said Mark Martin, founder of Dubai-based Martin Consulting LLC. “There seems to be no sense of urgent importance or escalation on the findings from the incident to ensure such events don’t take place again.”

The delay has left conspiracy theories to fill the void, Martin said.

--With assistance from Emma Dong.

©2023 Bloomberg L.P.