Another two executives of China Southern Airlines are being investigated amid an ongoing corruption probe in China's airline sector, sources close to the carrier told China Business News on June 27.

The two executives were in charge of planning and coordinating the flight routes of the carrier and its branch companies.

A director of the Civil Aviation Administration of China (CAAC), who was responsible for route approval, is also under investigation. This is the first investigation of CAAC headquarter staff.

Since June, nine executives of China Southern Airlines have been investigated after Huang Dengke, CAAC North China Regional Administration's chief, and Pang Hanzhang, Rimei Airlines manager, were charged with graft and insider trading.

CAAC has the final say when a carrier applies for a route. China Southern Airlines is suspected of seeking route permission through Pang Hanzhang.

Last Thursday, Liu Yajun, chief of Central and Southern Regional Administration (CSRA) of CAAC, committed suicide by throwing himself in front of a train.

Liu was moved to CSRA last February and was in charge of the approval of flight routes to Changsha, Guangzhou and other locations.

In the past six months, several senior aviation officials have been investigated, including Beijing airport chief Zhang Zhizhong, CAAC northern China branch director Huang Dengke, head of Civil Aviation Department of National Development and Reform Commission (NDRC) Kuang Xin, CAAC vice director Yu Renlu and Beijing airport vice manager Huang Gang.

China's business press carried the story above on Monday. China.org.cn has not checked the stories and does not vouch for their accuracy.