The China Great Wall Industries Corp is reported by Space News to have revealed the cause of the Long March 4B launch failure in December 2013. According to the report, the launch failure which destroyed the CBERS 3 (China Brazil Earth Resources Satellite 3) was caused by the premature shutdown of one of two YF-40 third stage engines. This was, in turn, caused by a blockage in a fuel line inlet. The blockage was due to debris clogging the inlet. The exact nature of the debris is unknown but believed to have been caused by either a manufacturing error or produced by the pressurization feeding system. New quality control procedures have been introduced to make sure that this fault does not happen again.
CBERS programme logo Courtesy: INPE/CAST