(Reuters) – Investigators looking into the crash of a China Eastern Airlines jet are examining the actions of the crew on the flight deck, with no evidence found of a technical malfunction, two people briefed on the matter said.

In mainland China’s deadliest aviation disaster for 28 years, the Boeing 737-800 crashed in the mountains of southern Guangxi on March 21, after a sudden plunge from cruising altitude, killing all 123 passengers and nine crew.

The pilots did not respond to repeated calls from air traffic controllers and nearby planes during the rapid descent, authorities have said.

On Tuesday, the Wall Street Journal said flight data from one of the black boxes indicated that someone in the cockpit intentionally crashed the plane, citing people familiar with the preliminary assessment of U.S. officials.

One source told Reuters that investigators were looking at whether the crash was a “voluntary” act involving crew inputs to the controls, though that does not necessarily mean the dive was intentional.

The cockpit voice recorder was damaged during the crash and it is unclear whether investigators have been able to retrieve any information from it.

Boeing, the maker of the jet, and the U.S. National Transportation Safety Board (NTSB) declined to comment and referred questions to Chinese regulators.

The Civil Aviation Administration of China (CAAC), which is leading the investigation, did not respond immediately to a request for comment.

SOURCE REUTERS