A General Electric jet engine that failed Sept. 11 in China didn’t have the cracked shaft that caused a similar engine to spew hot metal during a July 28 test in South Carolina, U.S. investigators said Thursday.

The National Transportation Safety Board, which is assisting the Civil Aviation Administration of China’s investigation, said in an emailed release that the GEnx engine on a Boeing 747-8 failed in Shanghai for different, as yet undetermined reasons.

Preliminary evidence from the Chinese investigation suggests the engine suffered relatively minor damage, according to two persons familiar with the probe. The type of damage doesn’t point to a systemic issue, one of the people said. They said they weren’t authorized to speak publicly about the investigation, which is continuing.

The NTSB previously said initial evidence in the Shanghai incident suggested a cracked mid-shaft, which is what caused a GEnx engine on a Boeing 787 to break apart in Charleston, S.C.

After the July 28 incident, inspectors discovered a second cracked shaft on a GEnx engine that hadn’t yet flown. The Federal Aviation Administration, which regulates the aviation industry, followed with an order for inspections.

Atlas Air Worldwide Holdings, the Purchase, N.Y.- based cargo carrier, is the only U.S. airline flying Boeing jets that fell under the FAA rule. Both of Atlas’s 747-8 cargo jets have been inspected and the engines didn’t have cracks, the company said in a release.

All in-service GEnx engines have now been inspected, according to the NTSB release.

The GEnx family of engines uses new technology and lighter materials to gain efficiency, according to GE’s website.