An Air China flight bound for Beijing made an unscheduled landing in the central Chinese city of Zhengzhou on Sunday after a passenger threatened a flight attendant with a fountain pen, the country’s civil aviation authority said.

In a brief statement on its website, the Civil Aviation Administration of China said a male passenger on Air China Flight 1350, attempted to use the pen to hold the flight attendant “under duress”, reported reuters.

Passengers and crew were unharmed, the statement said. 

Chinese police said preliminary investigations found the 41-year-old passenger, identified only by his last name Xu, had a “history of mental illness”. 

The flight took off from Changsha, the capital of southern Hunan province, at 8:40 a.m. and was scheduled to arrive at Beijing Capital International Airport at around 11 a.m., according to local media reports and flight tracking websites.

But it made the unscheduled landing at Zhengzhou Xinzheng International Airport, in central Henan province, at 9:58 a.m., according to an earlier post on Air China’s official Weibo microblog.

Air China said in the post that the plane made the unscheduled stop due to “public safety reasons”, and that police and civil aviation authorities were handling the situation.