On April 7, China Eastern Airlines admitted that last week's "disgraceful" incidents at its Yunnan Branch Co., where 21 flights departing the airport turned around and returned, were the result of a "human factor," most likely disgruntled pilots.

The flights, which were scheduled to leave Kunming for Dali, Lijiang, Banla, Mangshi, Simao and Lincang, took off but then returned, causing significant delays at the airport. CEA originally cited weather as an explanation even though other carriers operating from the provincial capital completed their flights successfully.

The airline said the incidents are under investigation and that it already has dismissed two senior officials from the Yunnan Branch Co. CAAC also is investigating, and both CEA and the regulator noted that "severe punishments" await the responsible parties once the events become clearer.

CEA is not alone in suffering from pilot discontent. Last month, 11 pilots from East Star Airlines took "collective leave" due to a labor dispute with the carrier while more than 40 Shanghai Airlines' pilots staged a sickout citing unfair treatment. In addition, 22 Hainan Airlines' pilots have resigned since 2006 without first securing permission from the company.