The National Transportation Safety Board has released an update on what caused a Boeing 787 Dreamliner’s General Electric-made engine failed late last month during a pre-flight taxi test in North Charleston.

“As a result of the investigative work to date, the NTSB has determined that a fan mid-shaft on the failed GEnx engine fractured at the forward end of the shaft, rear of the threads where the retaining nut is installed,” the Wednesday afternoon release said.

What that means in the big picture or what caused the fracture is not yet clear.

The NTSB release emphasized investigators in Cincinnati, Ohio are still examining the engine and a metallurgical analysis of its components. They have also begun to look at its manufacturing and assembly records.

The NTSB is also analyzing the affected plane’s cockpit voice recorder and flight data recorder at an agency laboratory in Washington D.C.

“This investigation is ongoing,” the release stated. “The information released today is factual in nature and does not include any analysis. Additional factual information may be released as it is developed.”

The NTSB sent an investigator to North Charleston the day after the July 28 incident, in which debris expelled from the plane’s engine started a small fire near the runway and shut down Charleston International Airport for more than an hour.

The NTSB launched a formal investigation into the mishap on July 31, and the agency’s team has been coordinating the disassembly and examination of the GEnx-1B engine at GE Aviation’s headquarters in Cincinnati ever since.

The engine suffered “significant back-end damage,” a GE Aviation spokesman said last week.

The debris did not pierce the engine’s casing, and no one was hurt. But given the 787 program’s history of technical glitches or supply-chain problems, the incident made international headlines.

The plane in question was the second S.C.-built Dreamliner. It was supposed to be among the first batch delivered to Air India, but those plans are now unclear.

Check back at postandcourier.com later and in Thursday’s editions of The Post and Courier for more details.